Response regulator homologues have complementary, light-dependent functions in the Arabidopsis circadian clock.
ABSTRACT TIMING OF CAB EXPRESSION 1 ( TOC1) functions with CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) in a transcriptional feedback loop that is important for the circadian clock in Arabidopsis thaliana (L.) Heynh. TOC1 and its four paralogues, the Arabidopsis PSEUDO-RESPONSE REGULATOR (PRR) genes, are expressed in an intriguing daily sequence. This was proposed to form a second feedback loop, similar to the interlocking clock gene circuits in other taxa. We show that prr9 and prr5 null mutants have reciprocal period defects for multiple circadian rhythms, consistent with subtly altered expression patterns of CCA1 and TOC1. The period defects are conditional on light quality and combine additively in double-mutant plants. Thus PRR9 and PRR5 modulate light input to the circadian clock but are neither uniquely required for rhythm generation nor form a linear series of mutual PRR gene regulation.
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ABSTRACT: The circadian clock perceives environmental signals to reset to local time, but the underlying molecular mechanisms are not well understood. Here we present data revealing that a member of the heat shock factor (Hsf) family is involved in the input pathway to the plant circadian clock. Using the yeast one-hybrid approach, we isolated several Hsfs, including HEAT SHOCK FACTOR B2b (HsfB2b), a transcriptional repressor that binds the promoter of PSEUDO RESPONSE REGULATOR 7 (PRR7) at a conserved binding site. The constitutive expression of HsfB2b leads to severely reduced levels of the PRR7 transcript and late flowering and elongated hypocotyls. HsfB2b function is important during heat and salt stress because HsfB2b overexpression sustains circadian rhythms, and the hsfB2b mutant has a short circadian period under these conditions. HsfB2b is also involved in the regulation of hypocotyl growth under warm, short days. Our findings highlight the role of the circadian clock as an integrator of ambient abiotic stress signals important for the growth and fitness of plants.Proceedings of the National Academy of Sciences 10/2014; · 9.81 Impact Factor
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ABSTRACT: During the last decade, significant research progress in Arabidopsis thaliana has been made in defining the molecular mechanisms behind the plant circadian clock. The circadian clock must have the ability to integrate both external light and ambient temperature signals into its transcriptional circuitry to properly regulate its function. We previously showed that transcription of a set of clock genes including LUX (LUX ARRHYTHMO), GI (GIGANTEA), LNK1 (NIGHT LIGHT-INDUCIBLE AND CLOCK-REGULATED GENE 1), PRR9 (PSEUDO-RESPONSE REGULATOR 9) and PRR7 is commonly regulated through the evening complex (EC) nighttime repressor in response to both moderate changes in temperature (Δ6°C) and differences in steady-state growth-compatible temperature (16°C to 28°C). Here, we further show that a nighttime-light signal also feeds into the circadian clock transcriptional circuitry through the EC nighttime repressor, so that the same set of EC target genes is upregulated in response to a nighttime-light pulse. This light-induced event is dependent on phytochromes, but not cryptochromes. Interestingly, both the warm-night and nighttime-light signals negatively modulate the activity of the EC nighttime repressor in a synergistic manner. In other words, an exponential burst of transcription of the EC target genes is observed only when these signals are simultaneously fed into the repressor. Taken together, we propose that the EC nighttime repressor plays a crucial role in modulating the clock transcriptional circuitry to properly keep track of seasonal changes in photo- and thermal-cycles by conservatively double-checking the external light and ambient temperature signals.Plant and Cell Physiology 10/2014; · 4.98 Impact Factor
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ABSTRACT: Functional redundancy often hampers the analysis of gene families. To overcome this difficulty, we constructed Arabidopsis thaliana lines that expressed artificial microRNAs designed to simultaneously target 2 to 6 paralogous genes encoding members of transcription factor families. Of the 576 genes that we chose as targets, only 122 had already been functionally studied at some level. As a simple indicator of the inhibitory effects of our amiRNAs on their targets, we examined the amiRNA-producing transgenic lines for morphological phenotypes at the rosette stage. Of 338 tested transgenes, 21 caused a visible morphological phenotype in leaves, a proportion much higher than that expected from insertional mutagenesis. Also, our collection likely represents many other mutant phenotypes. This robust, versatile method enables functional examination of redundant transcription factor paralogs and is particularly useful for genes that occur in tandem.This article is protected by copyright. All rights reserved.The Plant Journal 07/2014; · 6.82 Impact Factor