Rosette leaf

20 shoots

Inflorescence

IM 12

3

4

Inflorescence Meristem (IM)

Arabidopsis plant

Lecture 14: Regulation of flowering

Read: chapter 19, page 990-995Fig. 19.2, 3, 4, 5, 6, 7, 8Page:948-949

Four pathways

1. Photoperiod2. Vernalization3. Autonomous4. GA

Decision to flower(activation of

meristem identity genes)

(1) Photoperiod

Long-day: 16 hrs light, 8 hrs night

Short-day: 8 hrs light and 16 hrs night

Long-day plants: flower earlier under long-day conditions

Short-day plants: flower earlier under short-day conditionsDay-neutral plants: flowering unaffected by photoperiod

Photoperiod is detected by the leaves

FlorigenPhloem transport is involved

Fig. 19.3

Fig. 18.23 A-C

Phytochromes are photoreceptors that sense both photoperiod and light quality

tetrapyrrole

TKD: transmitter kinase domain

Cryptochrome

http://www.sciencemag.org/cgi/content/full/284/5415/760

CRY1 and CRY2 encodes homologues of DNAphotolyases which are flavin proteins that carry blue-light dependent electron transfer

PhyBD,E

Floral initiation

PhyA

Cry

Far red

Red

Blue

Early flowering mutants: correspond to repressor genesLate flowering mutants: correspond to activator genes

Genetics of Flowering

These genes could either act in signal productionor in signal reception (how will you tell?)

CONSTANS (CO) is a key gene in LD pathway

Fig. 19.5 Fig. 19.6

LD seedling

SD seedling

CO

AP2

Co: is a zinc-finger Tx factor

In leavesLight perception

by PhyA-E and CRY

Circadian clock:CCA1 and LHY

Activation of CO

Florigen?

In Shoot Apical MeristemActivation of meristem identity genes

LFY and AP1

Transport through the phloem

Four pathways

1. Photoperiod2. Vernalization3. Autonomous4. GA

Decision to flower(activation of

meristem identity genes)

(2) Vernalization pathway

Fig. 19.7 FRIGIDA (FRI) plants

Vernalization

cytosine demethylation

Genes involved in promoting flowering

Vernalization effect can be mimicked by treatment with demethylating agent 5-azacytidine

(3) Autonomous pathway

FLC (Flower locus C): MADS box protein

MADS box I K box COOHN

ABC gene

Meristem Identity Genes LFY and AP1

Long daypathway

Autonomouspathway

Vernalization pathway

GApathwayCO FLC

FRI

lfy-6

ap1-1

lfy-6 ap1-1

LEAFY (LFY)

Encode a novel protein

Can bind DNA in specific sequence in

vitro

RNA expressed in early floral meristem

LFY protein localizes to nuclei

LFY mRNALFY

35S::LFY converts shoots into flowers

Arabidopsis Aspen (Populus)