Inflorescence 14flowering.pdfFlorigen? In Shoot Apical Meristem Activation of meristem identity...
Transcript of Inflorescence 14flowering.pdfFlorigen? In Shoot Apical Meristem Activation of meristem identity...
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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
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Four pathways
1. Photoperiod2. Vernalization3. Autonomous4. GA
Decision to flower(activation of
meristem identity genes)
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(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
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Photoperiod is detected by the leaves
FlorigenPhloem transport is involved
Fig. 19.3
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Fig. 18.23 A-C
Phytochromes are photoreceptors that sense both photoperiod and light quality
tetrapyrrole
TKD: transmitter kinase domain
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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
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PhyBD,E
Floral initiation
PhyA
Cry
Far red
Red
Blue
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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?)
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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
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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
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Four pathways
1. Photoperiod2. Vernalization3. Autonomous4. GA
Decision to flower(activation of
meristem identity genes)
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(2) Vernalization pathway
Fig. 19.7 FRIGIDA (FRI) plants
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Vernalization
cytosine demethylation
Genes involved in promoting flowering
Vernalization effect can be mimicked by treatment with demethylating agent 5-azacytidine
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(3) Autonomous pathway
FLC (Flower locus C): MADS box protein
MADS box I K box COOHN
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ABC gene
Meristem Identity Genes LFY and AP1
Long daypathway
Autonomouspathway
Vernalization pathway
GApathwayCO FLC
FRI
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lfy-6
ap1-1
lfy-6 ap1-1
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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
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35S::LFY converts shoots into flowers
Arabidopsis Aspen (Populus)