Rosette leaf 2 0 shoots Inflorescence IM 1 2 3 4 Inflorescence Meristem (IM) Arabidopsis plant Lecture 14: Regulation of flowering Read: chapter 19, page 990-995 Fig. 19.2, 3, 4, 5, 6, 7, 8 Page:948-949
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)