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The plant clock and its outputs
Stacey Harmer
UC Davis
Copyright© Stacey Harmer 2008
The circadian clock regulates the timing
of many diverse processes
gene
gene expression
expression
photosynthesis
cell
elongation
cell elongation
light perception
cold responses
N & S assimilation
phenylpropanoid synthesis
flowering time
Copyright© Stacey Harmer 2008
hormone
hormonesignaling
signaling
starch mobilization
sugar metabolism
hypocotyl
height (mm)
Plant growth is clock‐regulated
Time in continuous light (hrs)
Dowson-Day (1999)
Plant J. 17:63-71
Copyright© Stacey Harmer 2008
A transcriptional feedback loop is at the
heart of the plant clock
LHY/
CCA1
CCA1/LHY
EE
TOC1
TOC1
Copyright© Stacey Harmer 2008
Many evening‐phased genes contain AAAATATCT (EE) in their promoter regions
Covington et al (2008)
Copyright© Stacey Harmer 2008
RVE1, a CCA1‐like protein,
binds the evening element
Copyright© Stacey Harmer 2008
Rawat et al (unpublished)
CCA1, LHY, and the RVE genes form a small gene family in Arabidopsis
Copyright© Stacey Harmer 2008
Rawat et al (unpublished)
RVE1 is co‐expressed with CCA1 and LHY
Copyright© Stacey Harmer 2008
Rawat et al (unpublished)
Overexpression of RVE1 causes arrhythmia
Rawat et al (unpublished)
Copyright© Stacey Harmer 2008
rve1 and rve1 rve2 rve7 mutants do not have clock phenotypes
Rawat et al (unpublished)
Copyright© Stacey Harmer 2008
RVE1‐OX have TALL and rve1 mutants have SHORT hypocotyls
Rawat et al (unpublished)
Copyright© Stacey Harmer 2008
CCA1 promotes stem growth via the bHLH factors PIF4 and PIF5
PIF4 and PIF5 are upregulated
in CCA1-OX plants
Nozue et al (2007)
Copyright© Stacey Harmer 2008
PIF4 and PIF5/PIL6 promote
stem growth
Fujimori et al (2004)
PIF4 and PIF5 expression is not altered in rve1 rve2 rve7 plants
Rawat et al (unpublished)
Copyright© Stacey Harmer 2008
PIF4 and PIF5 are not required for enhanced hypocotyl elongation in RVE1‐OX
Copyright© Stacey Harmer 2008
Rawat et al (unpublished)
RVE1‐OX and auxin overproducer phenotypes are similar
Curled cotyledons
Col
yuc1-d
Tall hypocotyl
Short root
RVE1-OX
Col
Zhao et al (2001)
Rawat et al (unpublished)
Copyright© Stacey Harmer 2008
Genes regulated by the growth‐promoting hormone are enriched for circadian control
Plants-In-Motion
Copyright© Stacey Harmer 2008
Covington et al (2008)
Auxin rescues the rve1 hypocotyl phenotype
Rawat et al (unpublished)
Copyright© Stacey Harmer 2008
Relative expression
A gene involved in auxin synthesis is upregulated in plants overexpressing LHY
Ler
LHY-OX
Time (hours)
Copyright© Stacey Harmer 2008
Michael et al (2008)
YUC8::GUS expression is increased in RVE1‐OX plants
cotyledon
root‐shoot junction
root‐tip
Col
RVE1‐OX
Rawat et al (unpublished)
Copyright© Stacey Harmer 2008
Rhythmic RVE1 expression is required for rhythmic auxin levels
Rawat et al (unpublished)
Copyright© Stacey Harmer 2008
RVE1 links the circadian clock to auxin signaling
AUXIN
RVE1
Copyright© Stacey Harmer 2008
The circadian clock regulates auxin signaling
WHY?
Plants-in-Motion
Perhaps it is important to coordinate growth with external light‐dark cycles
Copyright© Stacey Harmer 2008
Thanks…
UC Davis
Shajahan Anver
Mike Covington
Cory Ellison
Matt Jones
Richard La
Reetika Rawat
Koby Schwartz
Nozomu Takahashi
Elsewhere
Yunde Zhao
Youfa Cheng
Karin Ljung
Ilkka Sairanen
Steve Kay
Marty Straume