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, flowering, bud setting, tuberization, leaf senescence, juvenile to adult transition External factors: Temperature, nutrient availability, photoperiod, stress, water, hormones, light quality, light intensity Internal factors: developmental stage, age

Vegetative Reproductive Germination Juvenile Eucalyptus Juvenile vs Adult Leaves Juvenile Adult Open questions: developmental stage, temperature 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.

Flowering time integrators Light quality Vernalization Photoperiod Autonomous Gibberellin Signaling (SD) Flowering time integrators Meristem identity genes Floral Transition Photoperiod: short day/ long day plants, examples?, what other processes are regulated by photoperiod? Light quality influences photoperiod signaling Vernalization: extended long cold period enhances flowering. First studies done in grasses (winter wheat Many plants flower sooner or later due to the “activation” via the autonomous pathway. Gibberellins enhance flowering independently of FT, buty not all plants are responsive to Gi (maybe studies haven’t been done properly) How did they find all these genes? Putterill et al., 2004

Richard Amasino Summer and winter henbane (B) and Arabidopsis (C). Inductive photoperiods but no vernalization. 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 Li + Stockholm FRI allele Johansen et al., 2000

COL Natural variation of FRI alleles 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 FRI-Sf2 Ler Ler with a FRI allele from another accession is still early flowering MUTAGENESIS Col with a FRI allele from another accession Michaels & Amasino (1999)

(Michaels & Amasino 2000) Extra copies of FLC converts Arabidopsis to a biennial requiring vernalization to flower.

Who represses FLC? Light quality Vernalization Photoperiod 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 H3-K27 methylation VIN3: PHD (plant homeodomain protein)

Who activates FLC? Light quality Vernalization Photoperiod 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 ELF7 is the relative of yeast PAF1 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 ELF7 is the relative of yeast PAF1 He & Amasino 2005

FLC promoter modifications Methylation Acetylation FLC ELF7 is the relative of yeast PAF1 He & Amasino 2005

Conservation of the control of flowering? Flowering in long-day cereals

ARBIDOPSIS CEREALS Long days Long days PPD1 Vernalization Vernalization CO CO FRI FT* VRN2* VRN1 FT FLC 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

Thursday : Circadian Clock Photoperiodism

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vin3 vrn2 vrn1 4

BUT Who senses the cold directly?