Transcript Flowering: Vernalization

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
Vegetative
Eucalyptus Juvenile vs Adult Leaves
Juvenile
Adult
Reproductive
Adult
Time Transition to Flowering so
that Reproduction Occurs at
Appropriate Time of Year.
Spring/Summer-type annuals:
vernalization has no effect.
Winter-type annuals:
vernalization decreases time to
flowering.
Biennials: require vernalization
to flower.
Photoperiod
Light quality
Vernalization
Autonomous
Gibberellin
Signaling
(SD)
Flowering time integrators
Meristem identity genes
Floral Transition
How did they find all these genes?
Putterill et al., 2004
Summer and winter henbane (B) and
Arabidopsis (C).
Inductive photoperiods but no
vernalization.
Richard Amasino
Brassica oleracea (biennial cabbage).
Obligate vernalization requirement.
5 years without cold treatment.
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
Cloning of FRI
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)
Li
L
i
+
Johansen et al., 2000
Natural variation of FRI alleles
COL
Ler
Other factors involved
Johansen et al., 2000
Cloning of FLC: a MADS box protein induced by FRI
and repressed by cold
Cloning of FLC: problems neither Ler nor Col respond to vernalization
*Col has a non functioning FRI
*Ler has a weak FLC allele
Ler
MUTAGENESIS
Col with a FRI
allele from
another
accession
Ler FRI-Sf2
Ler with a FRI allele
from another
accession is still
early flowering
Michaels & Amasino (1999)
(Michaels & Amasino 2000)
Extra copies of FLC converts Arabidopsis to a biennial
requiring vernalization to flower.
Who represses FLC?
Photoperiod
Light quality
Vernalization
Autonomous
Gibberellin
Signaling
(SD)
Floral Transition
How does cold repress FLC expression?
Autonomous
pathway
Who represses FLC? The VRN genes
FCA
vrn mutants:
vrn1 and vrn2 have no memory but “feel” cold
vrn3 no memory nor cold sensation
Chandler et al., 1996
vrn2 mutants have no cold memory
VRN's are DNA binding proteins
VRN1: a B3-domain containing DNA binding protein (H3K9
methylation)
VRN2: component of Polycomb repressor complex that mediates H3K27 methylation
VIN3: PHD (plant homeodomain protein)
Who activates FLC?
Photoperiod
Light quality
Vernalization
Autonomous
PAF complex
Gibberellin
Signaling
(SD)
Floral Transition
PAF+ RNA polymerase II associated fact
What is the phenotype of PAF complex mutants?
Oh et al., 2004 (van Nocker lab)
He et al., 2004
Putterill et al., 2004
FLC
He & Amasino 2005
FLC expression and histone modifications
HIstones
ELF: early flowering
VIP: vernalization insensitive
PIE: photoperiod indpendent early flowering
H3-K4 methylation: gene activation
H3-K9, H3-K27 methylation: gene inactivation
FLC
He & Amasino 2005
FLC promoter modifications
Methylation
Acetylation
FLC
He & Amasino 2005
Conservation of the control of flowering?
Flowering in long-day cereals
ARBIDOPSIS
Long
days
Vernalization
FRI
CO
FT
CEREALS
FLC
Long
days
PPD1
Vernalization
CO
FT*
AP1
VRN1
Flowering
Flowering
Cereal genes:
VRN2: zinc-finger motif and CCT domain, similar to CO
VRN1: MADS box TF (as FLC, SOC1 etc.)
*modifications found in early flowering varieties
VRN2*
VRN1
Thursday :
•Circadian Clock
•Photoperiodism
2
2
3
3
vin3
vrn2
vrn1
4
BUT
Who senses the cold directly?