Flowering Time Control in Plants -How plants know the time to flower?

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Tobias Hart
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1 Advanced Molecular and Cell Biology II, 2015/12/04 Flowering Time Control in Plants -How plants know the time to flower? Masaki NIWA Grad. Sch. Biostudies, Kyoto Univ.

2 Why can plants bloom every year in the same season? They should know the best season to flower. Winter Spring Antelope Valley, California

3 How can plants know the season? -What is the environmental cues? Rainfall Temperature Sunshine hours Photoperiod

4 Molecular mechanisms in which plants know -Photoperiod -Temperature Winter Spring Antelope Valley, California

5 Arabidopsis thaliana life cycle (biennial accession) = 2 year life cycle Fall Long days Before cold Winter Short days During cold Summer Spring Long days After cold

6 Photoperiodism -the physiological reaction of organisms to the length of day or night. Change in color Migration Winter Summer Hibernation Flowering

7 Photoperiodism in plants Short days Long days Short-day (SD) plants flower when the day length is shorter than a critical length. e.g. rice Long-day (LD) plants flower when the day length is longer than a critical length. e.g. Arabidopsis

8 Do plants Plants monitor the the length of of day night. or night? = Plants are light-sensitive in night? Night break (Flash of light) Night break (Flash of light) Short-day (SD) plants Long-day (LD) plants

9 How do plants know the night length? -External coincidence model Pittendrigh and Minis (1964) Internal oscillator Subjective day Subjective night Long days External cue

10 How do plants know the night length? -External coincidence model Pittendrigh and Minis (1964) Internal oscillator Subjective day Subjective night Short days External cue

11 How do plants know the night length? -External coincidence model Pittendrigh and Minis (1964) Internal oscillator Subjective day Subjective night Short days +night break External cue night break night break

12 How do plants know the night length? -External coincidence model Pittendrigh and Minis (1964) Internal oscillator Subjective day = CO mrna/protein Subjective night

13 What is CONSTANS (CO)? Long days Short days wild type constans -CO promotes flowering under long days. -CO encodes a B-Box Zinc-Finger family protein. -CO activates FT (=florigen gene) transcription.

14 CO expression shows a constant diurnal oscillation CO mrna Suárez-Loópez et al., Nature (2001)

15 Molecular basis for the external coincidence model Internal oscillator = Subjective night CO mrna (= CO protein expression) Subjective day Suárez-Loópez et al., Nature (2001)

16 How is the internal oscillator generated? CO mrna Johansson and Staiger, J. Exp. Bot. (2015)

17 How do plants integrate internal and external signals? CO protein Blue light Blue light Red light Red light Johansson and Staiger, J. Exp. Bot. (2015), modified

18 CO protein is highly unstable in dark GFP-CO (constitutively expressed) autofluorescence Long days Short days Valverde et al., Science (2004), modified

19 CO protein is highly unstable in dark due to proteasome degradation Dark E3 ubiquitin ligase COP1 CO SPA Ub Ub Ub Ub CO COP1 SPA C O Laubinger et al., Development (2006) Jang et al., EMBO J. (2008) Light COP1 CRY2 SPA COP1 CRY1 CRY1 SPA Blue light Blue light Blue light receptor CO induction of downstream genes Zuo et al., Curr. Biol. (2011) Lian et al., Genes Dev. (2011) Liu et al., Genes Dev. (2011)

20 Molecular basis for the external coincidence model Internal oscillator = CO protein expression Long days External cue = CO protein stabilization CRY CRY Short days +night break

21 Molecular basis for the external coincidence model Internal oscillator = CO protein expression CO protein degradation Short days External cue = CO protein stabilization CRY CRY

22 Summary -photoperiod Internal oscillator Circadian clock in light CRY External cue blue light receptor CO mrna coincidence! CO protein in dark COP1-SPA Ubiquitin ligase FT, SOC1, (flowering activators)

23 How can plants know the season? Photoperiod + Photoperiod Temperature fall? spring?

24 Vernalization Arabidopsis (biennial accession) = 2 year life cycle SD 22 C LD 22 C SD 4 C LD 22 C LD 4 C LD 22 C

25 Vernalization Arabidopsis (annual accession) = 1 year life cycle = FLC SD 22 C LD 22 C

26 What is FLC? FLC: FLOWERING LOCUS C MADS-box transcription factor Dominant repressor of flowering Vernalization Photoperiod CO protein FLC FT, SOC1, (flowering activators)

27 Plants remember the temperature of previous 6 weeks?? Arabidopsis halleri subsp. gemmifera (perennial species) Aikawa et al., PNAS (2010) 42 days Cold experience -FLC expression level is most correlated when considering cold experience of past 42 days (= 6 weeks).

28 Cold memory is loaded on the chromatin. Before cold FLC is actively transcribed After cold FLC is completely repressed ( ) active marks H3K4me3 H3K36me3 acetylation H2Bub1 (H3K27me3) repressive marks FLC FLC LHP1

29 How is FLC chromatin structure changed? Before cold FLC PRC2 complex Nucleation region

30 How is FLC chromatin structure changed? During cold VIN3 is up-regulated during cold. Sung and Amashino, Nature (2004) FLC VIN3 VIN3 PHD-PRC2 complex PHD-PRC2 complex induces H3K27me3 in nucleation region. Finnegan and Dennis, Curr. Biol (2007)

31 How is FLC chromatin structure changed? After cold (warm temperature) Repressive marks spread throughout the gene body in a mitotically stable state. De Lucia et al., PNAS (2008) FLC PHD-PRC2 LHP1 CO protein FLC FT, SOC1,

32 Summary -vernalization Cold VIN3 ncrna FLC expression FT, SOC1, (flowering activators)

33 Summary -How can plants know the season? Fall CO + FLC + Winter CO - FLC Summer Spring CO + FLC -

Photoreceptor Regulation of Constans Protein in Photoperiodic Flowering

Photoreceptor Regulation of Constans Protein in Photoperiodic Flowering by Valverde et. Al Published in Science 2004 Presented by Boyana Grigorova CBMG 688R Feb. 12, 2007 Circadian Rhythms: The Clock Within