Israr KhanSoil science lab

Gyeongsang National University South Korea

Introduction

• Plants respond to stresses as individual cells and as whole

organisms

• stress induced signals can be transmitted throughout the plant,

making other parts more ready to withstand the stress.

• Plants must adapt to stresses because of their sedentary lifestyle

Stresses are abiotic or biotic

• Stresses cause responses inmetabolism and development

• Injuries occur in susceptibleplants, can lead to impedingflowering, death

ABIOTIC STRESSESEnvironmental, non-

biological

• Temperature (high / low)

• Water (high / low)

• Salt

• Radiation

• Chemical

BIOTIC STRESSESCaused by living

organisms

• Fungi

• Bacteria

• Insects

• Herbivores

• Other

plants/competition

Research background

• Plants have developed signaling systems to adapt environmental

changes

• ATP an important signaling molecule used by plants in various

processes including growth, development and stress responses.

• DORN1 was identified as the first plant purinoceptor essential for

plant response to ATP.

• To study the possible role of DORN1 for the research of role of

ATP in plants

• Small hydrophilic molecule

that consist of an adenine

base, a pentose sugar and

three phosphates.

• Energy currency in all

organisms

• Building block of genetic

material

• Extracellular signaling

molecule

Adenosine triphosphate (ATP)

DORN1?

• Also called as purinergic receptor found in

green plants

• DORN1 is a lectin receptor kinas (LecRK).

Functions

• Along with ATP acting as a DAMP

• Mediating wound-induced inflammatory

responses in green plants

• In response to cell lysis, ATP is discharged

and binds onto the extracellular lectin domain

of the DORN1 receptor.

• Intracellular DORN1 kinase domain is subsequently activated

• Activating mitogen-activated protein kinases

• increased cytosolic calcium concentration, and the induction of gene expression

Introduction

• ATP as a universal energy source for all organisms

• Cells have maintained high concentration of ATP inside

• Wounding, certain stimuli cause the release of ATP in to the

extracellular matrix which is recognized by PM based

purinoceptors.

• Animals have two purinoceptors

① P2X-ligand gated ion channels

② P2Y G protein coupled receptors

Introduction

• Muscle contraction, inflammation, neurotransmission, cell growth

and death

Function of ATP in animals

Extracellular ATP as a signal in plants

• Identification of the first plant purinoceptor (DORN1) have

stimulated greater interest in the role of extracellular signaling in

plants

Extracellular ATP and environmental plant responses

• Exogenous application of ATP can trigger elevation of

• Cellular Ca2+ concentration

• Production of nitric oxide (NO)

• Reactive oxygen species (ROS)

• Phosphatidic acid

• Activation of (MPK) phosphorylation

• These responses ultimately lead to the induction of gene

expression.

• About 600 genes in Arabidopsis responded to the addition of ATP

• A total of 322 genes were upregulated by ATP addition

• They hypothesized that ATP released from plants acts as an

intermediate signal to activate stress-responsive pathways.

Role of Extracellular ATP in plant responses to wounding

• Many stimuli including chemical, heat, pathogen attack, and other

stresses can trigger ATP release from cells, but the levels of ATP

released are usually very low

• In contrast, ATP levels released in response to wounding can

reach nearly 40 µM

• These data suggest that extracellular ATP released during

wounding as a damage associated molecular pattern (DAMP)

signal, which is then recognized by the DORN1 receptor

• ATP is well known as a DAMP signal in animals where it

contributes to the wound-induced inflammatory response which is

an important defense against short-term pathogen infection

Role of Extracellular ATP signaling in plant innate immunity

• ATP play an important role in plant innate immune responses

• It depends upon on

① Dose dependent

② Time dependent

• Short term treatment with ATP induced defense related gene

expression

• Exposure to high level of ATP was shown to trigger programmed

cell death in in populus euphratica

• Such treatments also leads to stomatal closure in Arabidopsis

• ATP addition was reported to trigger Ca increase in endoplasmic

reticulum and mitochondrion, which might link to apotosis.

A model for ATP action

• The role of an ATP is of great importance as a signal in plants

• Cytosolic ATP is released by physical wounding or other stresses.

• The released ATP directly binds to DORN1 which causes

intracellular signaling by activating DORN1’s kinase activity.

• Subsequently the signaling steps would lead to the induction of

calcium influx, ROS and NO production, MPK phosphorylation,

and gene expression.

• This pathway will activate those plant processes necessary to

protect the plant against environmental changes.

Figure:1. Functional categorization of ATP-upregulated genes using GO term enrichment test

based on Biological Processes. A list of GO terms was generated for 322 ATP-upregulated gen

es by AgriGO (<ce:inter-ref id="intr0005" href="http://bioinfo.cau.edu.cn/a...

Figure:2. An overview of ATP signaling pathway in plants. Cytosolic ATP is discharged outside the cell

via cell lysis (i.e. wounding), exocytosis, or active transport. The released ATP binds to

the extracellular lectin domain of the DORN1 receptor, which in turn activates the intracellular DORN1

kinase domain. Receptor activation ultimately leads to a variety f cellular responses, including increase

d cytosolic Ca2+, MAPK activation, and gene expression.

Conclusions

• These results strongly supports the existence of extracellular ATP

in plants and its role as a vital extra-cellular signal

• The identification of the DORN1 purinoceptor and studies of

plants lacking this receptor indicate that extracellular ATP is a

central signal involved in the plant response to a variety of

stresses.

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