advances in plant er architecture and dynamics · 1 1 advances in plant er architecture and...

24
1 Advances in plant ER architecture and dynamics 1 2 Giovanni Stefano and Federica Brandizzi* 3 4 MSU-DOE Plant Research Lab and Plant Biology Department, Michigan State 5 University, East Lansing, MI 48824, USA 6 7 * Correspondence to: [email protected] 8 9 Authors’ contributions: 10 G.S. and F.B. wrote the article. 11 12 Summary: Recent advances highlight mechanisms that enable the morphological 13 integrity of the plant ER in relation to the other organelles and the cytoskeleton. 14 15 16 ABSTRACT 17 The endoplasmic reticulum (ER) is a dynamic subcellular compartment that is 18 essential to eukaryotic life because it contributes significantly to the synthesis of 19 fundamental building blocks of the cell, including proteins and lipids, and it acts as an 20 important architectural scaffold to maintain a well-organized spatial distribution of 21 the other endomembrane organelles. Recent analyses with live cell imaging coupled 22 with genetics studies have brought to light the incredible dynamism of this organelle 23 and the underlying drivers as well as the impact of the ER organization on the general 24 cellular homeostasis and plant growth. In this review, we highlight the most recent 25 advances in the understanding of the mechanisms that enable the morphological 26 integrity of the plant ER in relation to the other organelles and the cytoskeleton. 27 28 INTRODUCTION 29 The endomembrane system comprises endocytic and biosynthetic cellular processes 30 that are closely integrated. At the core of the endomembrane system lays the 31 endoplasmic reticulum (ER), an essential and largely pleiotropic organelle. With its 32 network of interconnected tubules and flattened cisternae, the ER represents the 33 organelle with the largest membrane surface area and can be considered as the 34 Plant Physiology Preview. Published on October 6, 2017, as DOI:10.1104/pp.17.01261 Copyright 2017 by the American Society of Plant Biologists www.plantphysiol.org on February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Upload: others

Post on 28-Jan-2020

2 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

1

Advances in plant ER architecture and dynamics 1 2

Giovanni Stefano and Federica Brandizzi* 3 4

MSU-DOE Plant Research Lab and Plant Biology Department, Michigan State 5 University, East Lansing, MI 48824, USA 6 7 *Correspondence to: [email protected] 8 9 Authors’ contributions: 10 G.S. and F.B. wrote the article. 11 12 Summary: Recent advances highlight mechanisms that enable the morphological 13 integrity of the plant ER in relation to the other organelles and the cytoskeleton. 14 15 16 ABSTRACT 17 The endoplasmic reticulum (ER) is a dynamic subcellular compartment that is 18 essential to eukaryotic life because it contributes significantly to the synthesis of 19 fundamental building blocks of the cell, including proteins and lipids, and it acts as an 20 important architectural scaffold to maintain a well-organized spatial distribution of 21 the other endomembrane organelles. Recent analyses with live cell imaging coupled 22 with genetics studies have brought to light the incredible dynamism of this organelle 23 and the underlying drivers as well as the impact of the ER organization on the general 24 cellular homeostasis and plant growth. In this review, we highlight the most recent 25 advances in the understanding of the mechanisms that enable the morphological 26 integrity of the plant ER in relation to the other organelles and the cytoskeleton. 27 28 INTRODUCTION 29 The endomembrane system comprises endocytic and biosynthetic cellular processes 30 that are closely integrated. At the core of the endomembrane system lays the 31 endoplasmic reticulum (ER), an essential and largely pleiotropic organelle. With its 32 network of interconnected tubules and flattened cisternae, the ER represents the 33 organelle with the largest membrane surface area and can be considered as the 34

Plant Physiology Preview. Published on October 6, 2017, as DOI:10.1104/pp.17.01261

Copyright 2017 by the American Society of Plant Biologists

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 2: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

2

gatekeeper of the secretory pathway that controls multiple checkpoints in protein 35 biosynthesis: folding, quality control, signaling and degradation. In addition to 36 proteins such as receptors, ion channels, and enzymes, the ER synthesizes a wide 37 variety of cargo molecules that control a large spectrum of physiological and essential 38 processes, and are eventually shipped from the ER or retained in this organelle 39 (Aridor and Hannan, 2000; Kim and Brandizzi, 2016; Brandizzi, 2017). Furthermore, 40 with its function in controlling protein synthesis and folding, the ER has an important 41 role in abiotic and biotic stress resistance through the unfolded protein response 42 signaling (Angelos et al., 2017). The ER is also an important cellular compartment for 43 calcium storage and carbohydrate metabolism (Vitale and Denecke, 1999; Vitale and 44 Galili, 2001). 45 At a submicron level, the ER network is organized in domains that are 46 morphologically distinct and that assume specific functions (Staehelin, 1997). These 47 characteristics make of the ER a morphologically continuous cellular compartment 48 that is yet non-uniform at functional and structural level. In humans, alterations in 49 ER-mediated processes causes disease phenotypes that have been classified in three 50 groups: 1) cargo retention and degradation, 2) cargo accumulation and ER stress, 3) 51 ER transport machinery diseases (Aridor and Hannan, 2000). Also in plant cells, 52 defects in ER functionality leads to various developmental defects (Tamura et al., 53 2005; Conger et al., 2011; Stefano et al., 2012; Renna et al., 2013), supporting a 54 critical role of the ER for organism biology at large. 55 Morphologically, the ER is able to re-organize, enlarge and contract its highly 56 dynamic polygonal tubular network both spatially and temporally (Ridge et al., 1999; 57 Sparkes et al., 2009; Stefano et al., 2014). The integrity of the ER network structure is 58 important to maintain an efficient UPR, as demonstrated by the evidence that loss of 59 ER shaping proteins leads to attenuation of the UPR signaling in conditions of accrual 60 of unfolded secretory proteins in the ER (Lai et al., 2014). Therefore, there is a strong 61 connection between the morphology and the functional integrity of the ER. The plant 62 ER also entertains strong functional connections with other organelles including the 63 Golgi apparatus and the vacuole to which newly synthesized proteins can be exported 64 (Brandizzi et al., 2002; Shimada et al., 2003; Brandizzi, 2017) but also with 65 chloroplasts with which the ER synthesizes essential lipids (Hurlock et al., 2014; 66 Block and Jouhet, 2015). Possibly via direct connections, the ER movement 67 influences the movement of other organelles supporting an emerging model in cell 68

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 3: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

3

biology that the ER interaction with other organelles is important not only for the 69 exchange of constituents with other cellular compartments but also for their spatial 70 distribution and function (Stefano et al., 2014; Stefano et al., 2015) In this review, we 71 highlight some of the recent and exciting literature addressing the fundamental 72 questions on how the ER morphology and dynamics are controlled and how the ER 73 interacts with the cytoskeleton and other organelles in plant cells. 74 75 The ER is a pleomorphic organelle whose morphology and dynamics change 76 during the life of the cell 77 In general, the plant ER assumes the shape of a membrane network resembling the 78 arrangement of a spider web with interconnected tubules and cisternae within the cell. 79 Although the bulk of the ER is restricted at the cell cortex where it is sandwiched 80 between the tonoplast and the plasma membrane (PM), long ER tubular strands 81 characterized by a high streaming velocity cross along the central vacuole (Ueda et 82 al., 2010; Sparkes et al., 2011). Electron microscopy studies have revealed the 83 presence of smooth ER, rough ER and the nuclear envelope region (Hawes et al., 84 1981; Craig and Staehelin, 1988; Staehelin, 1997). The rough and smooth ER regions 85 are sub-domains with associated ribosomes or ribosome free regions, respectively. 86 The nuclear envelope is enwrapped by the ER resulting in a double membrane 87 delimiting the nucleus. Additionally, the ER passes through the plasmodesmata, 88 which are tiny channels that protrude into the cell wall and interconnect the cytoplasm 89 of neighboring cells (Carr, 1976; Wright and Oparka, 2006). These structures are 90 unique to plants and are crossed by a narrow tube-like structure, named desmotubule, 91 which is derived from the ER (Quader and Zachariadis, 2006; Knox et al., 2015; 92 Nicolas et al., 2017). As a result, the ER of each cell is interconnected to the 93 neighboring cells through these channels, forming therefore a virtually unique 94 organelle whose extension is not delimited by the cell’s boundaries. The ER is also 95 attached to the PM through ER-PM contact sites (EPCSs), which are largely immotile 96 subdomains of the ER that underlie the PM and whose number and density at the cell 97 cortex diminishes as cells expand (McFarlane et al., 2017). Fusion profiles of the ER 98 membrane with the PM at the EPCSs have not been observed; however proteins such 99 as VAP27 proteins and Synaptotagmin1 (SYT1) have been shown to accumulate at 100 the EPCSs (Wang et al., 2014; Levy et al., 2015; Perez-Sancho et al., 2015; Siao et 101 al., 2016; McFarlane et al., 2017). The VAP proteins are conserved across kingdoms 102

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 4: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

4

and possess three main regions, a C-terminal transmembrane domain, an N-terminal 103 major sperm domain and a coiled-coil domain (Wang et al., 2014). The VAP 104 subfamily of VAP27 proteins may contribute to ER anchoring to the cell surface via 105 the plasmodesmata as well as bridging the ER with the PM, through yet unknown 106 mechanisms that depend on cell wall integrity (Wang et al., 2016). The plant SYT1 is 107 a close ortholog of the yeast tricalbins and metazoan synaptotagmins that serve as ER-108 PM anchors in these non-plant cell systems. Similar to VAP27, SYT1 is localized to 109 the bulk ER and the EPCSs and SYT1 has been localized at EPCSs demarcated by 110 VAP27 (Perez-Sancho et al., 2015). Based on the ability of VAP27 to interact with 111 the plant-specific actin binding protein NET3c and microtubules, it appears that the 112 EPCSs marked by VAP27 may serve as ER-PM hubs where the two major 113 cytoskeletal components of plant cells converge(Wang et al., 2014). While roles for 114 non-plant EPCSs are emerging, including lipid homeostasis and Ca2+ influx (van der 115 Kant and Neefjes, 2014; Wakana et al., 2015), a physiological role for the plant 116 EPCSs is yet to be defined. It has been demonstrated that SYT1 interacts with 117 phospholipids possibly through electrostatic interactions and it may therefore bridge 118 the ER membrane with the PM. A loss of SYT1 reduces the ability of cells to 119 withstand mechanical pressure (Perez-Sancho et al., 2015), which may underlie a 120 function of these sites in the plant adaptation to abiotic stresses present in the natural 121 environment. The molecular mechanisms underlying such a role are yet to be 122 explored but the evidence that the EPCSs demarcated by SYT1 largely overlap with 123 VAP27-EPCSs suggests a functional connection between mechano-sensing and 124 cytoskeletal organization at these enigmatic sites. The identification of SYT1 and 125 VAP27 as components of the EPCS proteome opens up the exciting opportunity to 126 further define the EPCS constituents, which may provide additional tools to 127 understand the cellular role(s) of plant EPCSs. 128 With electron microscopy analyses, in addition to the EPCSs and plasmodesmata, the 129 plant ER has been found in contact also with other membranes including Golgi, 130 mitochondria, vacuole and plastids (Juniper et al., 1982; Staehelin, 1997). Indeed, 131 using laser trap technology, it has been shown that the ER physically contacts the 132 chloroplasts obtained from ruptured protoplasts expressing a fluorescent ER marker. 133 More specifically, it was shown that the released chloroplasts remained attached to 134 ER fragments that could be stretched out by optical tweezers. The applied force of 135 400 pN, which is a magnitude compatible with protein–protein interactions, could not 136

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 5: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

5

drag a chloroplast free from its attached ER (Andersson et al., 2007). Using confocal 137 imaging of a fluorescent fusion, the Brassica napus CLIP1 lipase/acylhydrolase 138 (BnCLIP1) has been recently detected in transient expression in tobacco at the ER-139 chloroplast contact sites (Tan et al., 2011), also known as PLAMs. BnCLIP1 enzyme 140 exhibited a discrete localization on the outer envelope membrane at the junction 141 between the ER and plastids. The subcellular distribution of a protein such as 142 BnCLIP1 at the PLAM is consistent with a potential role of these sites in the 143 coordinated synthesis of lipids between the ER and plastids (Tan et al., 2011). Yet it 144 is unknown whether proteins of this kind have only a biosynthetic role at the PLAMs, 145 such as lipid synthesis and transport, or they have a scaffolding role to tether the two 146 organelles together. 147 Using optical trapping and tweezer system, physical contacts of the ER with the Golgi 148 have been also established. In plant cells, the Golgi apparatus is dispersed into 149 polarized mini-stacks that are motile (Boevink et al., 1998; Nebenfuhr et al., 1999). 150 By trapping and pulling Golgi stacks in cells co-expressing fluorescent reporters for 151 the ER and for the Golgi, it was shown that the pulling of Golgi stacks in cells where 152 the movement of the ER and the Golgi was chemically inhibited was followed by a 153 movement of an ER tubule in association with the Golgi (Sparkes et al., 2009). 154 Recently, using a similar approach it was shown that overexpression of a truncated 155 membrane-anchored Golgi matrix protein AtCASP lacking the coiled-coil domain in 156 the cytosolic region could weaken the ER-Golgi connections, supporting the presence 157 of proteinaceous scaffolding that tethers the ER and the Golgi together (Osterrieder et 158 al., 2017). Although the identification of AtCASP as a putative ER-Golgi tether is a 159 landmark in plant cell biology, it will be important to pursue further the identification 160 of the proteins responsible for the tethering different membranes with the plant ER 161 not only at the Golgi but also with the PM and the other organelles in the plant cell. 162 This is a field that is considerably lagging behind compared to non-plant cell systems 163 (Rocha et al., 2009; Eden et al., 2010; Kornmann et al., 2011; Stefan et al., 2011; 164 Michel and Kornmann, 2012; Murley et al., 2015). 165 166 The ER changes shape during cell development 167 One of the most noticeable features visible through microscopy analyses of live cells 168 expressing bioreporters of the ER is the high dynamicity of this organelle; indeed the 169 ER tubules and cisternae continually move and rearrange evolving the overall 170

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 6: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

6

architecture during time and cell development. Curiously in plant cells, the ER does 171 not have only one form. Indeed during the life cycle of a plant cell, the ER undergoes 172 considerable reorganization of the morphology and dynamics (Figure 1) (Ridge et al., 173 1999; Stefano et al., 2014; McFarlane et al., 2017). Initial reports that the ER assumes 174 different shapes were provided over two decades ago in analyses using a fluorescent 175 probe for lipids (DiOC6) as well as a fluorescent protein targeted to the bulk ER 176 (Hepler PK, 1990; Ridge et al., 1999). The DiOC6 dye was used to explore the 177 structure of the ER in moss during bud formation. Noticeable changes in ER 178

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 7: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

7

architecture were established starting from a dense meshwork of membranes that was 179 re-organized into an open reticular network as the cell underwent growth. Through 180 analyses performed using a fluorescent protein tagged to the ER on root and 181 hypocotyl cells of Arabidopsis it was possible to distinguish an ER characterized by 182 lamellar sheets in early phases of cell expansion followed by a change toward a 183 reticulate tubular structure, which is typical of the ER of fully-expanded cells (Ridge 184 et al., 1999). It was also noticed that in fully expanded root epidermal cells that give 185 origin to the root hair, the reticular ER network was condensed at the sites where the 186 root hair is formed (Ridge et al., 1999). The organization of the ER morphology 187 becomes even more puzzling in dividing Pinus root cells in which the ER at 188 preprophase and prophase is spatially rearranged to overlay the microtubules (MTs) 189 (Quader and Zachariadis, 2006). Indeed treatment with oryzalin, a MT inhibitor, 190 affects the formation of the tubular endoplasmic reticulum-preprophase band (tER-191 PPB), tER-metaphase spindle, and tER phragmoplast, suggesting that at least in Pinus 192 root cells the ER network organization may depend on MTs during mitosis and 193 cytokinesis. Although together these results support that the ER assumes different 194 morphology during cell growth, it is yet to be shown whether there may be a 195 functional link between the shape of the ER and the ER function at specific stages of 196 cell growth and development. It has been recently shown that mutations in the ER-197 shaping protein Root Hair Defective 3 (RHD3) compromise not only the overall 198 organization of the ER and the transition from extensive sheet-like form to a 199 reticulated pattern, but also cell elongation (Stefano et al., 2014). These results 200 therefore support the existence of a close connection between the ER shape and cell 201 elongation although the underlying mechanisms are yet to be defined. Based on the 202 evidence that the loss of RHD3 alters the distribution of auxin in roots (Stefano et al., 203 2015), increases the cell’s phospholipid content and leads to an attenuation of the 204 unfolded protein response of the ER (Lai et al., 2014; Maneta-Peyret et al., 2014), the 205 relationship between ER morphology and cell growth may be the sum of several 206 processes that are affected by the alteration of ER architecture. 207 208 209 The ER dynamics depend on the cytoskeleton and ER shaping proteins 210 In fully-expanded cells, the ER network is highly pleiotropic. Despite an anchoring to 211 stable EPCSs, the network undergoes profound rearrangements through tubule 212

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 8: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

8

interconversion into other tubules as well fusion of tubules with cisternae. While 213 processes of fission/fragmentation have been verified in non-plant cells systems, such 214 as sea urchin, starfish, lacrimal cells and non-neuronal cell lines (Terasaki and Jaffe, 215 1991; Jaffe and Terasaki, 1993; Subramanian and Meyer, 1997; Dayel et al., 1999; 216 Ribeiro et al., 2000; Harmer et al., 2002; Kucharz et al., 2009), the common profiles 217 for rearrangement of the plant ER are homotypic membrane fusion and tubule 218 emergence from other tubules. These rearrangements are guided primarily by the 219 actin cytoskeleton (Sparkes et al., 2009), with the MTs offering a minor yet 220 significant contribution. Specifically, MTs guide ER tubule extension with an almost 221 20-fold slower rate compared to actin-based extension, and MTs appear to provide 222 anchoring for the formation of multiway junctions (Hamada et al., 2014). While the 223 identity of the proteins connecting the plant ER to the MTs are yet unknown, recently 224 two proteins have been shown to link ER to actin. The first protein identified, SYP73 225 belongs to the three-member SYP7 family of plant-specific SNAREs (Sanderfoot et 226 al., 2000). These proteins, named SYP71, SYP72 and SYP73, share a high degree of 227 sequence similarity (Sanderfoot et al., 2000; Cao et al., 2016). 228 SYP73 binds actin directly and possesses a short luminal domain, a putative 229 transmembrane domain and a cytosolic region, which contains an actin-binding motif 230 (Cao et al., 2016). SYP73 is primarily localized to the ER. In conditions of 231 overexpression of SYP73 the architecture of the ER changes dramatically with a 232 reduction of the cisternal profiles and a network pattern that overlaps the actin 233 filaments. Conversely, a loss of SYP73 causes enlargement of the ER, reduces its 234 streaming and compromises cell elongation at the (Cao et al., 2016). These results 235 pose that SYP73 is an ER-actin linker. SYP73 is only one of the components of the 236 SYP family; therefore other SYP proteins might share similar functions that may be 237 important in different developmental stages. The other protein implicated in ER-actin 238 connection is NET3B (NETWORKED 3B), which is a plant-specific protein 239 belonging to a superfamily containing 13 members (Hawkins et al., 2014). All NET 240 proteins contain two important domains. In the C-terminal region a predicted coiled-241 coil domain may be important for protein-protein interactions, and the second 242 important domain that characterizes this family is the NET-actin-binding (NAB) 243 domain, which may act as an adapter to link membranes to the actin cables. In 244 particular, NET3B has been shown to associate in vivo with the ER. When the protein 245 fused with a fluorescent marker is overexpressed, similarly to conditions of SYP73 246

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 9: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

9

overexpression, the architecture ER rearranges into resembling the actin cytoskeleton 247 (Wang and Hussey, 2017). Although differently from SYP73, a direct interaction of 248 NET3B with actin has not been established yet, these results suggest that NET3B may 249 function as a linker between the ER and actin. Analysis of a NET3B knockout did not 250 show any significant defects when compared to wild type (Wang and Hussey, 2017), 251 suggesting that there may be functional redundancy among the NET proteins. 252 253 While the cytoskeleton provides a dynamic framework for the overall ER 254 architecture, ER proteins such as reticulons and RHD3 have important role in the 255 shaping of the network. Reticulons are membrane integral proteins that assume a 256 wedge-like topology with their transmembrane regions (Voeltz et al., 2006; Nziengui 257 et al., 2007; Sparkes et al., 2010). By inserting into the membrane, the reticulons form 258 low-mobility oligomers and induce high curvature of the ER membrane which results 259 in the formation and stabilization of tubules (Shibata et al., 2008; Hu et al., 2011). 260 Consistent with this function, overexpression of Arabidopsis RTN13, a reticulon that 261 localizes at the ER tubules and the edges of ER cisternae, causes constrictions of the 262 ER lumen and reduces the diffusion of lumen markers in the ER (Tolley et al., 2008; 263 Tolley et al., 2010). The function of RTN13 depends on a small conserved domain at 264 the C-terminal region that contains a putative amphipathic helix (APH). Deletion of 265 APH did not impair oligomer formation but disrupted the membrane-shaping function 266 of RTN13 in vivo. These results are important as they support that the membrane 267 shaping function of reticulons may not be linked to their ability to oligomerize but to 268 the presence of the APH domain. The plant family of reticulons contains 21 members 269 (Nziengui et al., 2007; Sparkes et al., 2010). Given the large size of this family and 270 the possibility that reticulons may share overlapping functions, no phenotype of the 271 ER network in knock-outs has been reported. Nonetheless, it would be interesting to 272 carry out complementation tests with reticulons lacking the APH to pinpoint the 273 molecular role of this domain in the context of ER shaping. 274 In addition to the reticulons, RHD3 has important shaping activity at the ER. RHD3 is 275 an ER-integral protein with two putative transmembrane domains. A defective allele 276 of RHD3 was first identified in a screen for root hair defects (Schiefelbein and 277 Somerville, 1990). Loss of function of RHD3 leads to a reduced elongation of cells of 278 the primary root (Stefano et al., 2012). At a subcellular level, the loss of RHD3 also 279 reduces the formation of three-way junction owing to the capacity of the protein to 280

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 10: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

10

fuse membranes in a GTP-dependent fashion (Ueda et al., 2016). In this context, 281 RHD3 functions analogously to similar membrane-associated dynamin-like GTPases, 282 such as metazoan atlastin and yeast Sey1p (Chen et al., 2011; Zhang et al., 2013; Yan 283 et al., 2015). Nonetheless, it has been shown that the functional regulation of RHD3 284 may depend on plant-unique features. In particular, overexpression of the C-terminal 285 region of RHD3 (RHD3 amino acids 677–802) disrupts the ER network integrity; 286 conversely, overexpression of the analogous Sey1p region (Sey1p amino acids 682–287 776) does not (Stefano and Brandizzi, 2014). Intriguingly, the C-terminus domain of 288 RHD3 is phosphorylated and it has been shown that kinase treatment of RHD3 289 induces oligomerization of this protein, which in turn may modulate its ER-shaping 290 function (Ueda et al., 2016). 291 One puzzling question about RHD3 in relation to ER shape in general concerns the 292 physiological role of ER membrane fusion. RHD3 belongs to a three-member family 293 of proteins composed of RHD3, RHD3-like 1 and RHD3-like 2. The evidence that a 294 double deletion of RHD3 and RHD3-like 1 is lethal and that the combined loss of 295 RHD3 and RHD3-like 2 causes pollen lethality (Zhang et al., 2013) suggests that the 296 formation of the tubular ER network is extremely important for the cell. Nonetheless, 297 the evidence that in very young cells the ER does not have a reticulated form raises 298 the question on how the shape of the ER may influence the physiology of cells at 299 certain stages of growth compared to others. 300 In addition to reticulons and RHD3 proteins, there may be other proteins involved in 301 ER shape. For example, in non-plant cells, the DP1/YOP1 proteins work as ER 302 shapers in synergy with the reticulons. In Arabidopsis five Yop1 homologues have 303 been identified in the HVA22 family of proteins (Brands and Ho, 2002). One of this 304 HVA22 protein fused with a fluorescent protein is localized at the ER with RHD3 305 (Chen et al., 2011). A functional characterization of HVA22 proteins in the context of 306 ER shape is lacking and it cannot be excluded that additional proteins may be 307 involved in plant ER architecture. In metazoans and yeast, it has been shown that 308 lunapark (Lnp1), a two transmembrane domain protein, is required for ER shaping. In 309 particular, Lnp1 has been implicated in contributing to the tubule-to-sheet conversion 310 most likely by stabilizing the tree-way ER junctions (Chen et al., 2015; Wang et al., 311 2016). A ortholog of Lnp1 does not seem to be present in the Arabidopsis genome, 312 suggesting that other proteins may have analogous functions to Lnp1 or that the 313

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 11: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

11

stabilization of the plant ER junctions depends on different mechanisms compared to 314 non-plant cell systems. 315 316 ER movement and cytoplasmic streaming: more than molecular tracks and 317 motors? 318 While in animal cells, the rearrangement of the ER network as well as transport of 319 vesicles largely depend on MTs, in plant cells this role is served primarily by actin 320 and myosin motor proteins, like the plant-specific myosin XI-K (Li and Nebenfuhr, 321 2007; Prokhnevsky et al., 2008; Peremyslov et al., 2010; Ueda et al., 2010). Indeed, 322 the loss of myosin compromises the movement of ER, Golgi stacks, peroxisome and 323 mitochondria (Peremyslov et al., 2008; Ueda et al., 2010), which collectively is called 324 cytoplasmic streaming (Woodhouse and Goldstein, 2013; Stefano et al., 2014). The 325 biological role of cytoplasmic streaming has not been established at a molecular level 326 but it is plausible to hypothesize that, owing to the presence of a large central vacuole 327 that can occupy up to 90% of the total cell volume, the movement of the cytoplasmic 328 content may facilitate the delivery of nutrients as well as communication between 329 distal sites in the cells. The ER network is a pervasive organelle that contacts 330 heterotypic membranes(Andersson et al., 2007; Mehrshahi et al., 2013; Stefano et al., 331 2015) and it may have therefore a bearing on their movement. Indeed, as plant cells 332 expand, concomitantly with the changes of the ER architecture from a cisternal to a 333 tubular morphology, the velocity of ER streaming as well as overall cytoplasmic 334 streaming increases (Stefano et al., 2014). Based on this evidence and the findings 335 that the loss of RHD3 compromises the spatial distribution as well as the streaming 336 not only of the ER but also of other organelles, such as the Golgi, peroxisomes, 337 mitochondria and endosomes, during cell expansion, it has been suggested that the ER 338 movement may contribute to the general cytoplasmic streaming through the physical 339 connections that it established with heterotypic membranes (Stefano et al., 2014; 340 Stefano et al., 2015). Intriguingly, a disruption of endocytosis has been verified in 341 connection with the loss of ER streaming and disruption of ER morphology in an 342 RHD3 mutant (Stefano et al., 2015). These results support the hypothesis that the 343 dynamic positioning of organelles such as endosomes is important to ensure their 344 function and maintain the overall cell homeostasis. 345 CONCLUDING REMARKS 346

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 12: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

12

We are witnessing an exciting era for the understanding of the plant ER. Although in 347 recent years enormous advances have been made towards the understanding of how 348 the structure and dynamic architecture of the ER are maintained, it is yet unknown 349 how other fundamental aspects of the ER are established, including how ER 350 subdomains attain and maintain their identity and what their cellular role may be. 351 Some ER subdomains have been recently investigated and the existence of an 352 association between the ER and endosomes and the identity of the molecular players 353 involved in the association of the ER with the PM or actin has been established. The 354 proteins and regulatory processes underlying homotypic tubule fusion are also 355 emerging (Figure 2). One of the challenges for the next years will be to gain higher 356 resolution of the three-dimensional architecture of the ER in relation to other 357 organelles and the cytoskeleton. This will be likely achievable with electron 358 tomography that allows visualizing structures at a high resolution (6-8 nm) (Donohoe 359 et al., 2006). An example of the power of this method is provided by a recently study 360 using cryo-electron tomography showing at molecular resolution the 3D architecture 361 of ER-PM contact sites in non plant-cells (Fernandez-Busnadiego et al., 2015). This 362 approach is likely to lead to more insights on the recently discovered linkage of the 363 ER with cytoskeleton and the other components of the endomembrane system in plant 364 cells. 365 366 ACKNOWLEDGMENTS 367 We acknowledge support by the Chemical Sciences, Geosciences and Biosciences 368 Division, Office of Basic Energy Sciences, Office of Science, US Department of 369 Energy (award number DE-FG02-91ER20021) for infrastructure, and the National 370 Science Foundation (MCB 1714561) and AgBioResearch to FB. 371 372 373 374 375 376 377 378 379 FIGURES AND LEGENDS 380

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 13: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

13

381 382 Figure 1. In plant cells, ER architecture is correlated to cell expansion. Confocal 383 images of wild-type Arabidopsis thaliana Col-0 cotyledon epidermal cells expressing 384 an ER lumen marker ERYK (Nelson et al., 2007) at different phases of cell expansion 385 . Note the change in the morphology of the ER network, which from a most cisternal 386 appearance in cells 3 days after germination (DAG) assumes progressively a more 387 reticulated organization as cells expand. Scale bar: 5 μm. 388

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 14: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

14

389 390 Figure 2. Diagram showing the association between the ER and other organelles in a 391 plant cell. CW = cell wall, PM = plasma membrane, PD = plasmodesma, V = 392 vacuole, ER = endoplasmic reticulum, N = nucleus, Px = peroxisome, Mt = 393 mitochondrion, GA = Golgi stack, En = endosome, MT = microtubule. Black 394 numbered square regions indicate the ER-organelle associations or ER rearrangement 395 properties identified in plant cell. 396 397 398 399 400 401

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 15: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

ADVANCES

• The ER morphology and dynamics undergo significant changes during cell development. These changes are disrupted by mutations in the ability of the ER tubules to fuse homotipically.

• An ER fusogen, RHD3 has been identified and its function appears to be controlled by plant-specific mechanisms.

• The reticulons function as ER membrane shapers also in plants. The identification of a key functional domain in a reticulon poses a new and possibly conserved mechanism underlying the ER-shaping role.

• Components of the ER-plasma membrane contact sites have been identified. Although the function of these sites is still not completely known, they may function as cytoskeletal hubs and have a role in mechano-sensing.

• The dynamics and positioning of the ER depends not only on the actin-myosin cytoskeleton but also on microtubules.

• The ER is attached to other organelles. Disruption of the ER organization and dynamics affects the positioning and streaming of other organelles.

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 16: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

OUTSTANDING QUESTIONS

• Are there other proteins besides RHD3 and reticulons to shape the ER membrane?

• Is the shape of other organelles influenced by the ER architecture?

• Are ER shape and dynamics important to generate other organelles de novo?

• How does the ER connect to microtubules?

• How are the proteins linking ER and cytoskeleton elements spatially distributed and functionally controlled during cell cycle and development?

• Are plant EPCSs proteins required for the developmental transition of the ER shape during cell growth?

• What are the molecular components of the contact sites of the ER with other organelles?

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 17: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

Parsed CitationsAndersson MX, Goksor M, Sandelius AS (2007) Optical manipulation reveals strong attracting forces at membrane contact sitesbetween endoplasmic reticulum and chloroplasts. J Biol Chem. 282: 1170-1174

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Angelos E, Ruberti C, Kim SJ, Brandizzi F (2017) Maintaining the factory: the roles of the unfolded protein response in cellularhomeostasis in plants. Plant J 90: 671-682

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Aridor M, Hannan LA (2000) Traffic jam: a compendium of human diseases that affect intracellular transport processes. Traffic 1: 836-851

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Block MA, Jouhet J (2015) Lipid trafficking at endoplasmic reticulum-chloroplast membrane contact sites. Curr Opin Cell Biol 35: 21-29Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Boevink P, Oparka K, Santa Cruz S, Martin B, Betteridge A, Hawes C (1998) Stacks on tracks: the plant Golgi apparatus traffics on anactin/ER network. Plant J 15: 441-447

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Brandizzi F (2017) Transport from the endoplasmic reticulum to the Golgi in plants: Where are we now? Semin Cell Dev Biol10.1016/j.semcdb.2017.06.024

Brandizzi F, Snapp EL, Roberts AG, Lippincott-Schwartz J, Hawes C (2002) Membrane protein transport between the endoplasmicreticulum and the Golgi in tobacco leaves is energy dependent but cytoskeleton independent: evidence from selectivephotobleaching. Plant Cell 14: 1293-1309

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Brands A, Ho TH (2002) Function of a plant stress-induced gene, HVA22. Synthetic enhancement screen with its yeast homolog revealsits role in vesicular traffic. Plant Physiol 130: 1121-1131

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Cao P, Renna L, Stefano G, Brandizzi F (2016) SYP73 Anchors the ER to the Actin Cytoskeleton for Maintenance of ER Integrity andStreaming in Arabidopsis. Curr Biol 26: 3245-3254

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Carr DJ (1976) Historical Perspectives on Plasmodesmata. In BES Gunning, AW Robards, eds, Intercellular Communication in Plants:Studies on Plasmodesmata, 10.1007/978-3-642-66294-2_14. Springer Berlin Heidelberg, Berlin, Heidelberg, pp 291-295

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Chen J, Stefano G, Brandizzi F, Zheng H (2011) Arabidopsis RHD3 mediates the generation of the tubular ER network and is requiredfor Golgi distribution and motility in plant cells. J Cell Sci 124: 2241-2252

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Chen S, Desai T, McNew JA, Gerard P, Novick PJ, Ferro-Novick S (2015) Lunapark stabilizes nascent three-way junctions in theendoplasmic reticulum. Proc Natl Acad Sci U S A 112: 418-423

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Conger R, Chen Y, Fornaciari S, Faso C, Held MA, Renna L, Brandizzi F (2011) Evidence for the involvement of the ArabidopsisSEC24A in male transmission. J Exp Bot 10.1093/jxb/err174

Pubmed: Author and Title www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from

Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 18: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

CrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Craig S, Staehelin LA (1988) High pressure freezing of intact plant tissues. Evaluation and characterization of novel features of theendoplasmic reticulum and associated membrane systems. Eur J Cell Biol 46: 81-93

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Dayel MJ, Hom EF, Verkman AS (1999) Diffusion of green fluorescent protein in the aqueous-phase lumen of endoplasmic reticulum.Biophys J 76: 2843-2851

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Donohoe BS, Mogelsvang S, Staehelin LA (2006) Electron tomography of ER, Golgi and related membrane systems. Methods 39: 154-162

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Eden ER, White IJ, Tsapara A, Futter CE (2010) Membrane contacts between endosomes and ER provide sites for PTP1B-epidermalgrowth factor receptor interaction. Nat Cell Biol 12: 267-272

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Fernandez-Busnadiego R, Saheki Y, De Camilli P (2015) Three-dimensional architecture of extended synaptotagmin-mediatedendoplasmic reticulum-plasma membrane contact sites. Proc Natl Acad Sci U S A 112: E2004-2013

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Hamada T, Ueda H, Kawase T, Hara-Nishimura I (2014) Microtubules contribute to tubule elongation and anchoring of endoplasmicreticulum, resulting in high network complexity in Arabidopsis. Plant Physiol 166: 1869-1876

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Harmer AR, Gallacher DV, Smith PM (2002) Correlations between the functional integrity of the endoplasmic reticulum and polarizedCa2+ signalling in mouse lacrimal acinar cells: a role for inositol 1,3,4,5-tetrakisphosphate. Biochem J 367: 137-143

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Hawes CR, Juniper BE, Horne JC (1981) Low and high voltage electron microscopy of mitosis and cytokinesis in maize roots. Planta152: 397-407

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Hawkins TJ, Deeks MJ, Wang P, Hussey PJ (2014) The evolution of the actin binding NET superfamily. Front Plant Sci 5: 254Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Hepler PK PB, Lancelle SA, McCauley MM, Lichtscheidl I (1990) Cortical endoplasmic reticulum in plants. J Cell Sci 96: 355–373Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Hu J, Prinz WA, Rapoport TA (2011) Weaving the web of ER tubules. Cell 147: 1226-1231Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Hurlock AK, Roston RL, Wang K, Benning C (2014) Lipid trafficking in plant cells. Traffic 15: 915-932Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Jaffe LA, Terasaki M (1993) Structural changes of the endoplasmic reticulum of sea urchin eggs during fertilization. Dev Biol 156: 566-573

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from

Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 19: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

Juniper BE, Hawes CR, Horne JC (1982) The Relationships between the Dictyosomes and the Forms of Endoplasmic Reticulum inPlant Cells with Different Export Programs. Botanical Gazette 143: 135-145

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Kim SJ, Brandizzi F (2016) The plant secretory pathway for the trafficking of cell wall polysaccharides and glycoproteins. Glycobiology26: 940-949

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Knox K, Wang P, Kriechbaumer V, Tilsner J, Frigerio L, Sparkes I, Hawes C, Oparka K (2015) Putting the Squeeze on Plasmodesmata: ARole for Reticulons in Primary Plasmodesmata Formation. Plant Physiol 168: 1563-1572

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Kornmann B, Osman C, Walter P (2011) The conserved GTPase Gem1 regulates endoplasmic reticulum-mitochondria connections.Proc Natl Acad Sci U S A 108: 14151-14156

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Kucharz K, Krogh M, Ng AN, Toresson H (2009) NMDA receptor stimulation induces reversible fission of the neuronal endoplasmicreticulum. PLoS One 4: e5250

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Lai YS, Stefano G, Brandizzi F (2014) ER stress signaling requires RHD3, a functionally conserved ER-shaping GTPase. J Cell Sci 127:3227-3232

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Levy A, Zheng JY, Lazarowitz SG (2015) Synaptotagmin SYTA forms ER-plasma membrane junctions that are recruited toplasmodesmata for plant virus movement. Curr Biol 25: 2018-2025

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Li JF, Nebenfuhr A (2007) Organelle targeting of myosin XI is mediated by two globular tail subdomains with separate cargo bindingsites. J Biol Chem 282: 20593-20602

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Maneta-Peyret L, Lai YS, Stefano G, Fouillen L, Brandizzi F, Moreau P (2014) Phospholipid biosynthesis increases in RHD3-defectivemutants. Plant Signal Behav 9: e29657

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

McFarlane HE, Lee EK, van Bezouwen LS, Ross B, Rosado A, Samuels AL (2017) Multiscale Structural Analysis of Plant ER-PM ContactSites. Plant Cell Physiol 58: 478-484

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Mehrshahi P, Stefano G, Andaloro JM, Brandizzi F, Froehlich JE, DellaPenna D (2013) Transorganellar complementation redefines thebiochemical continuity of endoplasmic reticulum and chloroplasts. Proc Natl Acad Sci U S A 110: 12126-12131

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Michel AH, Kornmann B (2012) The ERMES complex and ER-mitochondria connections. Biochem Soc Trans 40: 445-450Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Murley A, Sarsam RD, Toulmay A, Yamada J, Prinz WA, Nunnari J (2015) Ltc1 is an ER-localized sterol transporter and a component ofER-mitochondria and ER-vacuole contacts. J Cell Biol 209: 539-548

Pubmed: Author and TitleCrossRef: Author and Title www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from

Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 20: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

Google Scholar: Author Only Title Only Author and Title

Nebenfuhr A, Gallagher LA, Dunahay TG, Frohlick JA, Mazurkiewicz AM, Meehl JB, Staehelin LA (1999) Stop-and-go movements ofplant Golgi stacks are mediated by the acto-myosin system. Plant Physiol 121: 1127-1142

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Nelson BK, Cai X, Nebenfuhr A (2007) A multicolored set of in vivo organelle markers for co-localization studies in Arabidopsis andother plants. Plant J 51: 1126-1136

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Nicolas WJ, Grison MS, Trepout S, Gaston A, Fouche M, Cordelieres FP, Oparka K, Tilsner J, Brocard L, Bayer EM (2017) Architectureand permeability of post-cytokinesis plasmodesmata lacking cytoplasmic sleeves. Nat Plants 3: 17082

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Nziengui H, Bouhidel K, Pillon D, Der C, Marty F, Schoefs B (2007) Reticulon-like proteins in Arabidopsis thaliana: structuralorganization and ER localization. FEBS Lett 581: 3356-3362

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Osterrieder A, Sparkes IA, Botchway SW, Ward A, Ketelaar T, de Ruijter N, Hawes C (2017) Stacks off tracks: a role for the golginAtCASP in plant endoplasmic reticulum-Golgi apparatus tethering. J Exp Bot 10.1093/jxb/erx167

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Peremyslov VV, Prokhnevsky AI, Avisar D, Dolja VV (2008) Two class XI myosins function in organelle trafficking and root hairdevelopment in Arabidopsis. Plant Physiol 146: 1109-1116

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Peremyslov VV, Prokhnevsky AI, Dolja VV (2010) Class XI myosins are required for development, cell expansion, and F-Actinorganization in Arabidopsis. Plant Cell 22: 1883-1897

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Perez-Sancho J, Vanneste S, Lee E, McFarlane HE, Esteban Del Valle A, Valpuesta V, Friml J, Botella MA, Rosado A (2015) TheArabidopsis synaptotagmin1 is enriched in endoplasmic reticulum-plasma membrane contact sites and confers cellular resistance tomechanical stresses. Plant Physiol 168: 132-143

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Prokhnevsky AI, Peremyslov VV, Dolja VV (2008) Overlapping functions of the four class XI myosins in Arabidopsis growth, root hairelongation, and organelle motility. Proc Natl Acad Sci U S A 105: 19744-19749

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Quader H, Zachariadis M (2006) The Morphology and Dynamics of the ER. In DG Robinson, ed, The Plant Endoplasmic Reticulum,10.1007/7089_063. Springer Berlin Heidelberg, Berlin, Heidelberg, pp 1-23

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Renna L, Stefano G, Majeran W, Micalella C, Meinnel T, Giglione C, Brandizzi F (2013) Golgi traffic and integrity depend on N-myristoyltransferase-1 in Arabidopsis. Plant Cell 25: 1756-1773

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Ribeiro CM, McKay RR, Hosoki E, Bird GS, Putney JW, Jr. (2000) Effects of elevated cytoplasmic calcium and protein kinase C onendoplasmic reticulum structure and function in HEK293 cells. Cell Calcium 27: 175-185

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 21: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

Ridge RW, Uozumi Y, Plazinski J, Hurley UA, Williamson RE (1999) Developmental transitions and dynamics of the cortical ER ofArabidopsis cells seen with green fluorescent protein. Plant Cell Physiol 40: 1253-1261

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Rocha N, Kuijl C, van der Kant R, Janssen L, Houben D, Janssen H, Zwart W, Neefjes J (2009) Cholesterol sensor ORP1L contacts theER protein VAP to control Rab7-RILP-p150 Glued and late endosome positioning. J Cell Biol 185: 1209-1225

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Sanderfoot AA, Assaad FF, Raikhel NV (2000) The Arabidopsis genome. An abundance of soluble N-ethylmaleimide-sensitive factoradaptor protein receptors. Plant Physiol 124: 1558-1569

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Schiefelbein JW, Somerville C (1990) Genetic Control of Root Hair Development in Arabidopsis thaliana. Plant Cell 2: 235-243Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Shibata Y, Voss C, Rist JM, Hu J, Rapoport TA, Prinz WA, Voeltz GK (2008) The reticulon and DP1/Yop1p proteins form immobileoligomers in the tubular endoplasmic reticulum. J Biol Chem 283: 18892-18904

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Shimada T, Fuji K, Tamura K, Kondo M, Nishimura M, Hara-Nishimura I (2003) Vacuolar sorting receptor for seed storage proteins inArabidopsis thaliana. Proc Natl Acad Sci U S A 100: 16095-16100

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Siao W, Wang P, Voigt B, Hussey PJ, Baluska F (2016) Arabidopsis SYT1 maintains stability of cortical endoplasmic reticulum networksand VAP27-1-enriched endoplasmic reticulum-plasma membrane contact sites. J Exp Bot 67: 6161-6171

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Sparkes I, Hawes C, Frigerio L (2011) FrontiERs: movers and shapers of the higher plant cortical endoplasmic reticulum. Curr OpinPlant Biol 10.1016/j.pbi.2011.07.006

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Sparkes I, Runions J, Hawes C, Griffing L (2009) Movement and remodeling of the endoplasmic reticulum in nondividing cells oftobacco leaves. Plant Cell 21: 3937-3949

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Sparkes I, Tolley N, Aller I, Svozil J, Osterrieder A, Botchway S, Mueller C, Frigerio L, Hawes C (2010) Five Arabidopsis reticulonisoforms share endoplasmic reticulum location, topology, and membrane-shaping properties. Plant Cell 22: 1333-1343

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Sparkes IA, Ketelaar T, de Ruijter NC, Hawes C (2009) Grab a Golgi: laser trapping of Golgi bodies reveals in vivo interactions with theendoplasmic reticulum. Traffic 10: 567-571

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Staehelin LA (1997) The plant ER: a dynamic organelle composed of a large number of discrete functional domains. Plant J 11: 1151-1165

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Stefan CJ, Manford AG, Baird D, Yamada-Hanff J, Mao Y, Emr SD (2011) Osh proteins regulate phosphoinositide metabolism at ER-plasma membrane contact sites. Cell 144: 389-401

Pubmed: Author and TitleCrossRef: Author and Title

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 22: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

Google Scholar: Author Only Title Only Author and Title

Stefano G, Brandizzi F (2014) Unique and conserved features of the plant ER-shaping GTPase RHD3. Cell Logist 4: e28217Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Stefano G, Renna L, Brandizzi F (2014) The endoplasmic reticulum exerts control over organelle streaming during cell expansion. JCell Sci 127: 947-953

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Stefano G, Renna L, Lai Y, Slabaugh E, Mannino N, Buono RA, Otegui MS, Brandizzi F (2015) ER network homeostasis is critical forplant endosome streaming and endocytosis. Cell Discov 1: 15033

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Stefano G, Renna L, Moss T, McNew JA, Brandizzi F (2012) In Arabidopsis, the spatial and dynamic organization of the endoplasmicreticulum and Golgi apparatus is influenced by the integrity of the C-terminal domain of RHD3, a non-essential GTPase. Plant J. 69:957-966

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Subramanian K, Meyer T (1997) Calcium-induced restructuring of nuclear envelope and endoplasmic reticulum calcium stores. Cell 89:963-971

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Tamura K, Shimada T, Kondo M, Nishimura M, Hara-Nishimura I (2005) KATAMARI1/MURUS3 Is a novel golgi membrane protein that isrequired for endomembrane organization in Arabidopsis. Plant Cell 17: 1764-1776

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Tan X, Wang Q, Tian B, Zhang H, Lu D, Zhou J (2011) A Brassica napus lipase locates at the membrane contact sites involved inchloroplast development. PloS one 6: e26831

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Terasaki M, Jaffe LA (1991) Organization of the sea urchin egg endoplasmic reticulum and its reorganization at fertilization. J Cell Biol114: 929-940

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Tolley N, Sparkes I, Craddock CP, Eastmond PJ, Runions J, Hawes C, Frigerio L (2010) Transmembrane domain length is responsiblefor the ability of a plant reticulon to shape endoplasmic reticulum tubules in vivo. Plant J 64: 411-418

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Tolley N, Sparkes IA, Hunter PR, Craddock CP, Nuttall J, Roberts LM, Hawes C, Pedrazzini E, Frigerio L (2008) Overexpression of aplant reticulon remodels the lumen of the cortical endoplasmic reticulum but does not perturb protein transport. Traffic 9: 94-102

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Ueda H, Yokota E, Kutsuna N, Shimada T, Tamura K, Shimmen T, Hasezawa S, Dolja VV, Hara-Nishimura I (2010) Myosin-dependentendoplasmic reticulum motility and F-actin organization in plant cells. Proc Natl Acad Sci U S A 107: 6894-6899

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Ueda H, Yokota E, Kuwata K, Kutsuna N, Mano S, Shimada T, Tamura K, Stefano G, Fukao Y, Brandizzi F, Shimmen T, Nishimura M,Hara-Nishimura I (2016) Phosphorylation of the C Terminus of RHD3 Has a Critical Role in Homotypic ER Membrane Fusion inArabidopsis. Plant Physiol 170: 867-880

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 23: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

van der Kant R, Neefjes J (2014) Small regulators, major consequences - Ca(2)(+) and cholesterol at the endosome-ER interface. J CellSci 127: 929-938

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Vitale A, Denecke J (1999) The endoplasmic reticulum-gateway of the secretory pathway. Plant Cell 11: 615-628Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Vitale A, Galili G (2001) The endomembrane system and the problem of protein sorting. Plant Physiol 125: 115-118Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Voeltz GK, Prinz WA, Shibata Y, Rist JM, Rapoport TA (2006) A class of membrane proteins shaping the tubular endoplasmic reticulum.Cell 124: 573-586

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Wakana Y, Kotake R, Oyama N, Murate M, Kobayashi T, Arasaki K, Inoue H, Tagaya M (2015) CARTS biogenesis requires VAP-lipidtransfer protein complexes functioning at the endoplasmic reticulum-Golgi interface. Mol Biol Cell 26: 4686-4699

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Wang P, Hawkins TJ, Richardson C, Cummins I, Deeks MJ, Sparkes I, Hawes C, Hussey PJ (2014) The plant cytoskeleton, NET3C, andVAP27 mediate the link between the plasma membrane and endoplasmic reticulum. Curr Biol 24: 1397-1405

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Wang P, Hussey PJ (2017) NETWORKED 3B: a novel protein in the actin cytoskeleton-endoplasmic reticulum interaction. J Exp Bot 68:1441-1450

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Wang P, Richardson C, Hawkins TJ, Sparkes I, Hawes C, Hussey PJ (2016) Plant VAP27 proteins: domain characterization, intracellularlocalization and role in plant development. New Phytol 210: 1311-1326

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Wang S, Tukachinsky H, Romano FB, Rapoport TA (2016) Cooperation of the ER-shaping proteins atlastin, lunapark, and reticulons togenerate a tubular membrane network. Elife 5

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Woodhouse FG, Goldstein RE (2013) Cytoplasmic streaming in plant cells emerges naturally by microfilament self-organization. ProcNatl Acad Sci U S A 110: 14132-14137

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Wright KM, Oparka KJ (2006) The ER Within Plasmodesmata. In DG Robinson, ed, The Plant Endoplasmic Reticulum, 10.1007/7089_060.Springer Berlin Heidelberg, Berlin, Heidelberg, pp 279-308

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Yan L, Sun S, Wang W, Shi J, Hu X, Wang S, Su D, Rao Z, Hu J, Lou Z (2015) Structures of the yeast dynamin-like GTPase Sey1p provideinsight into homotypic ER fusion. J Cell Biol 210: 961-972

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

Zhang M, Wu F, Shi J, Zhu Y, Zhu Z, Gong Q, Hu J (2013) RHD3 family of dynamin-like GTPases mediates homotypic endoplasmicreticulum fusion and is essential for Arabidopsis development. Plant Physiol 163: 713-720

Pubmed: Author and TitleCrossRef: Author and TitleGoogle Scholar: Author Only Title Only Author and Title

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.

Page 24: Advances in plant ER architecture and dynamics · 1 1 Advances in plant ER architecture and dynamics 2 3 Giovanni Stefano and Federica Brandizzi* 4 5 MSU-DOE Plant Research Lab and

www.plantphysiol.orgon February 12, 2020 - Published by Downloaded from Copyright © 2017 American Society of Plant Biologists. All rights reserved.