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?