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Temporal Repression of Core Circadian Genes Is Mediated through EARLY FLOWERING 3 in Arabidopsis

2011; Elsevier BV; Volume: 21; Issue: 2 Linguagem: Inglês

10.1016/j.cub.2010.12.013

1879-0445

Laura E. Dixon, Kirsten Knox, László Kozma‐Bognár, Megan M. Southern, Alexandra Pokhilko, Andrew J. Millar,

Photosynthetic Processes and Mechanisms

Summary The circadian clock provides robust, ∼24 hr biological rhythms throughout the eukaryotes. The clock gene circuit in plants comprises interlocking transcriptional feedback loops, reviewed in [1], whereby the morning-expressed transcription factors CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) repress the expression of evening genes, notably TIMING OF CAB EXPRESSION 1 ( TOC1 ). EARLY FLOWERING 3 ( ELF3 ) has been implicated as a repressor of light signaling to the clock [2, 3] and, paradoxically, as an activator of the light-induced genes CCA1 and LHY [4, 5]. We use cca1-11 lhy-21 elf3-4 plants to separate the repressive function of ELF3 from its downstream targets CCA1 and LHY . We further demonstrate that ELF3 associates physically with the promoter of PSEUDO-RESPONSE REGULATOR 9 ( PRR9 ), a repressor of CCA1 and LHY expression, in a time-dependent fashion. The repressive function of ELF3 is thus consistent with indirect activation of LHY and CCA1 , in a double-negative connection via a direct ELF3 target, PRR9 . This mechanism reconciles the functions of ELF3 in the clock network during the night and points to further effects of ELF3 during the day.