Photoperiod & Circadian Rhythms Eva Farre

Photoperiod Light qualityVernalization Autonomous Gibberellin Signaling (SD) Floral Transition PAF complex

Which processes are regulated by photoperiodism?

How could day length be measured?

Hour glass model External coincidence model Internal coincidence model Yanovsky & Kay 2003

You need:

The circadian clock “gates” signaling pathways: flowering Imaizumi and Kay, 2006

Circadian concepts Harmer 2008

How to study circadian clocks? CAB2:LUCIFERASE COTYLEDON MOVEMENT OTHERS?

Mechanisms of circadian clocks EukaryotesProkaryotes Activator Repressor Delays Transcriptional/translational feedback loops KaiC KaiC-P Posttranslational regulation "feedbackloops" AND Trc/Trl feedbackloops

Mechanisms of circadian clocks in vivo in vitro KAIC Nakajima et al., 2005 (Kondo lab)

The Arabidopsis circadian clock: transcriptional regulation CCA1/LHY: : morning expressed transcription factors TOC1: evening expressed pseudo-response regulator (also called PRR1) 1. Expression level TOC1 CCA1/LHY Delays Alabadi et al., 2001

The Arabidopsis circadian clock: transcriptional regulation CCA1/LHY: : morning expressed transcription factors TOC1: evening expressed pseudo-response regulator (also called PRR1) 2. DNA binding: In vitro A. Finding the responsible promoter element B. Testing for binding: CCA1 gel shift assay TOC1:LUC

The Arabidopsis circadian clock: transcriptional regulation 2. DNA binding: In vivo, Chromatin Immunoprecipitation CCA1 is associated with the TOC1 promoter Perales et al., 2007 TOC1 is associated with CCA1 promoter, probably through a TCP TF (CHE1) Pruneda-Paz et al., 2009

The Arabidopsis circadian clock 2009 status

The Arabidopsis circadian clock: Posttranscriptional regulation Translation: LHY Phosphorylation: CCA1: CK2 PRRs: unknown kinases Protein stability: PRRs Light dependent protein-protein interactions: ZTL

A significant number of genes have cycling RNA levels Michael et al., 2008

Many processes are gated (i.e. regulated by the clock) Fowler et al., 2005 Thomashow lab for example: cold OTHERS?

Photoperiod Light qualityVernalization Autonomous Gibberellin Signaling (SD) Floral Transition PAF complex

CONSTANS expression is regulated by the clock Short DaysLong Days toc1 mutants have a short period and flower early CO+ light high FT early flowering External does not match internal rhythm Expternal matches internal rhythm late flowering

CONSTANS expression and natural variation Bohlenius et al., 2006

What happens in short day plants? Dark/COP1

What experiments would you do to prove that FT protein and/or RNA is florigen ?

FT is Florigen Notaguchi et al., 2008 Corbesier et al., 2007

Zeevaart, 2008 FT is Florigen FD= bZIP transcription factor

Photoperiod Light qualityVernalization Autonomous Gibberellin Signaling (SD) Floral Transition PAF complex

FKF = Flavin-binding, kelch repeat, F-box 1

Vierstra 2003

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Which other important protein is also expressed exclusively in the vascular tissue? 2.

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Sawa et al., 2005

ZTL family of proteins are blue light receptors