Post on 24-Dec-2015
Regulation of Development: Vernalization
Eva Farre
Topics :•Overview on developmental transitions•Overview on the regulation of flowering•Regulation of flowering: vernalization
Which developmental transitions occur in plants?
Which factors regulate them?
Germination
Juvenile
Adult
Adult
Eucalyptus Juvenile vs Adult Leaves
Juvenile Vegetative
Reproductive
Time Transition to Flowering so Time Transition to Flowering so that Reproduction Occurs at that Reproduction Occurs at Appropriate Time of Year.Appropriate Time of Year.
Spring/Summer-type annuals: Spring/Summer-type annuals: vernalization has no effect.vernalization has no effect.
Winter-type annuals: Winter-type annuals: vernalization decreases time to vernalization decreases time to flowering.flowering.
Biennials: require vernalization Biennials: require vernalization to flower.to flower.
PhotoperiodLight quality Vernalization
Autonomous
GibberellinSignaling (SD)
Floral Transition
Putterill et al., 2004
How did they find all these genes?
Flowering time integrators
Meristem identity genes
Richard AmasinoRichard Amasino
Brassica oleracea (biennial cabbage).Obligate vernalization requirement.5 years without cold treatment.
Summer and winter henbane (B) and Arabidopsis (C).Inductive photoperiods but no vernalization.
Vernalization (status 1996):
*the promotion of flowering in response to prolonged exposure to low temperature (2-8 weeks at 4C).
*Accelerates flowering of most late flowering mutants, the one that more is fca.
*Quantitative relationship between length of cold treatment and acceleration of flowering (Napp-Zinn, 1987)
*Transmitted by mitosis but not meiosis (Evans, 1960)
*DNA metylation might be involved (Burns et all, 1993)
*FRIGIDA FLOWERING-LOCUS C
Napp-Zinn (1955):
“The following aspects of the subject are reviewed: (1) conventional analysis of vernalization genes in wheat, peas and Arabidopsis; (2) population genetics and gene geography; and (3) physiological genetics”.
Arabidopsis Stockholm (late) vs Li5 (early)
Cloning of FRI
Li Li + Stockholm FRI allele
Johansen et al., 2000
Other factors involved
COL
Ler
Johansen et al., 2000
Natural variation of FRI alleles
Cloning of FLC: problems neither Ler nor Col respond to vernalization*Col has a non functioning FRI*Ler has a weak FLC allele
Col with a FRI allele from another accession
LLererLLer FRI-Sf2er FRI-Sf2
Ler with a FRI allele from another accession is still early flowering
Cloning of FLC: a MADS box protein induced by FRI and repressed by cold
Michaels & Amasino (1999)
MUTAGENESIS
Extra copies of FLC converts Arabidopsis to a biennial Extra copies of FLC converts Arabidopsis to a biennial requiring vernalization to flower.requiring vernalization to flower.
(Michaels & Amasino 2000)
Who represses FLC?
PhotoperiodLight quality Vernalization
Autonomous
GibberellinSignaling (SD)
Floral Transition
How does cold repress FLC expression?
Autonomous pathwayAutonomous pathway
FCAFCA
vrn mutants:vrn1 and vrn2 have no memory but “feel” coldvrn3 no memory nor cold sensation
Who represses FLC? The VRN genes
Chandler et al., 1996
vrn2 mutants have no cold memory
VRN1: a B3-domain containing DNA binding protein (H3K9 methylation)
VRN2: component of Polycomb repressor complex that mediates H3-K27 methylation
VIN3: PHD (plant homeodomain protein)
VRN's are DNA binding proteins
PhotoperiodLight quality Vernalization
Autonomous
GibberellinSignaling (SD)
Floral Transition
Putterill et al., 2004
PAF complex
PAF+ RNA polymerase II associated factWhat is the phenotype of PAF complex mutants? Oh et al., 2004 (van Nocker lab)
He et al., 2004
Who activates FLC?
He & Amasino 2005
FLC
HIstones
FLC expression and histone modifications
ELF: early floweringVIP: vernalization insensitivePIE: photoperiod indpendent early flowering
H3-K4 methylation: gene activation
H3-K9, H3-K27 methylation: gene inactivation
He & Amasino 2005
FLC
He & Amasino 2005
FLC
Methylation
Acetylation
FLC promoter modifications
Conservation of the control of flowering?Flowering in long-day cereals
Long days
CO
FT
AP1
Flowering
Long days
PPD1
CO
FT*
VRN1
Flowering
FLC
FRI
Vernalization Vernalization
VRN2* VRN1
Cereal genes:VRN2: zinc-finger motif and CCT domain, similar to COVRN1: MADS box TF (as FLC, SOC1 etc.)*modifications found in early flowering varieties
ARBIDOPSIS CEREALS
Thursday :•Circadian Clock•Photoperiodism
2
2
3
3
4
vin3
vrn2
vrn1
BUT
Who senses the cold directly?