Reciprocal Regulation Between TOC1 and LHY / CCA1 Within the Arabidopsis Circadian Clock

Abstract

The interactive regulation between clock genes is central for oscillator function. Here, we show interactions between the Arabidopsis clock genes LATE ELONGATED HYPOCOTYL (LHY), CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), and TIMING OF CAB EXPRESSION 1 (TOC1). The MYB transcription factors LHY and CCA1 negatively regulate TOC1 expression. We show that both proteins bind to a region in the TOC1 promoter that is critical for its clock regulation. Conversely, TOC1 appears to participate in the positive regulation of LHY and CCA1 expression. Our results indicate that these interactions form a loop critical for clock function in Arabidopsis.

The role of microRNAs (miRNA) in circadian rhythmicity

“…These negative factors, which physically interact with each other, producing heterodimers (e.g. mouse PER-CRY, or fly PER-TIM), are later shuttled back to the nucleus where they repress the positive circadian transcription factors, thereby downregulating their own transcription (Darlington et al 1998;Kume et al 1999;Lee et al 2000;Alabadi et al 2001). The decrease in abundance in the negative factors later in the circadian cycle gradually leads to their own derepression, allowing the positive transcription factor to drive a new circadian cycle.…”

Abiotic stress and the plant circadian clock

“…The formers are two Myb-related transcription factors, CIRCADIAN CLOCK ASSOCIATED (CCA1) and LATE ELONGATED HYPOCOTYL (LHY ), 10,11 whose encoded proteins bind to the Evening Element (EE) in the promoter of TIMING OF CAB EXPRESSION/PSEUDORESPONSE REGULATOR1 (TOC1/PRR1), the evening component. 12 This binding represses TOC1 transcription, but at dusk the protein levels of CCA1 and LHY diminish and the repression of TOC1 is relieved. As a consequence, TOC1 mRNA reaches its maximum around dusk, and by an unknown mechanism, TOC1 protein activates the transcription of CCA1 and LHY, 12,13 and it has been proposed that this is direct.…”

“…12 This binding represses TOC1 transcription, but at dusk the protein levels of CCA1 and LHY diminish and the repression of TOC1 is relieved. As a consequence, TOC1 mRNA reaches its maximum around dusk, and by an unknown mechanism, TOC1 protein activates the transcription of CCA1 and LHY, 12,13 and it has been proposed that this is direct. 14,15 The role of CCA1/LHY and TOC1 as core elements has been confirmed by genetic experiments.…”

A Genetic Screen for Leaf Movement Mutants Identifies a Potential Role for AGAMOUS-LIKE 6 (AGL6) in Circadian-Clock Control

“…Although the overall amplitude and expression level of LHY were reduced in agl6-1D plants, the period length and phase were similar to those of wild-type plants. In addition, the clear circadian expression pattern of TOC1, an evening gene (Alabadi et al, 2001;Strayer et al, 2000), in wild-type plants had disappeared in agl6-1D plants. Overall TOC1 expression seemed to be arrhythmic in agl6-1D plants.…”