LWD–TCP complex activates the morning gene CCA1 in Arabidopsis

Abstract

A double-negative feedback loop formed by the morning genes CIRCADIAN CLOCK ASSOCIATED1 (CCA1)/LATE ELONGATED HYPOCOTYL (LHY) and the evening gene TIMING OF CAB EXPRESSION1 (TOC1) contributes to regulation of the circadian clock in Arabidopsis. A 24-h circadian cycle starts with the peak expression of CCA1 at dawn. Although CCA1 is targeted by multiple transcriptional repressors, including PSEUDO-RESPONSE REGULATOR9 (PRR9), PRR7, PRR5 and CCA1 HIKING EXPEDITION (CHE), activators of CCA1 remain elusive. Here we use mathematical modelling to infer a co-activator role for LIGHT-REGULATED WD1 (LWD1) in CCA1 expression. We show that the TEOSINTE BRANCHED 1-CYCLOIDEA-PCF20 (TCP20) and TCP22 proteins act as LWD-interacting transcriptional activators. The concomitant binding of LWD1 and TCP20/TCP22 to the TCP-binding site in the CCA1 promoter activates CCA1. Our study reveals activators of the morning gene CCA1 and provides an action mechanism that ensures elevated expression of CCA1 at dawn to sustain a robust clock.

Phylogenomic analysis of MKKs and MAPKs from 16 legumes and detection of interacting pairs in chickpea divulge MAPK signalling modules

“…The plant-specific TCP transcription factor family is known for its role in plant growth, development, immunity, and circadian clock regulation 21, 22 . Thus, we were interested in exploring the possibility of a legume MAPK targeting TCP transcription factors and adding another layer of regulation in TCP complexes.…”

TCP Transcription Factors at the Interface between Environmental Challenges and the Plant’s Growth Responses

“…Not only TCP21, other TCPs have also been found to bind to CCA1 in yeast based studies and co-immunoprecipitation experiments (Giraud et al, 2010; Pruneda-Paz et al, 2014). A recent study also showed that TCP20 and TCP22 act as activators of CCA1 in the morning, fulfilling an important role in the circuity of the circadian clock (Wu et al, 2016). This means that TCP proteins bind to the promoters of clock genes, regulate their expression, dimerize with clock proteins and bind to downstream targets of the clock (Pruneda-Paz et al, 2009, 2014; Giraud et al, 2010; Wu et al, 2016) ( Figure 3 ).…”

“…A recent study also showed that TCP20 and TCP22 act as activators of CCA1 in the morning, fulfilling an important role in the circuity of the circadian clock (Wu et al, 2016). This means that TCP proteins bind to the promoters of clock genes, regulate their expression, dimerize with clock proteins and bind to downstream targets of the clock (Pruneda-Paz et al, 2009, 2014; Giraud et al, 2010; Wu et al, 2016) ( Figure 3 ). Altogether, it becomes clear that TCPs not only affect growth via the cell cycle.…”

Evolving Tale of TCPs: New Paradigms and Old Lacunae

“…For example, a WD repeat-containing protein, LIGHT-REGULATED WD1 (LWD1) acts as a coactivator of TCP20 and 22 in regulating expression of morning gene CIRCADIAN CLOCK ASSOCIATED1 ( CCA1 ) in Arabidopsis (Wu et al, 2016). Although TCP20 and 22 can bind to regulatory element in CCA1 promoter, even in the absence of LWDs, overexpression of TCP20 / 22 in lwd1lwd2 double mutant fails to activate CCA1 expression (Wu et al, 2016). Whether concomitant binding of TCPs and LWDs leads to any shifts in conformational state of TCPs is yet to be determined.…”