Transcriptional regulation of the arabidopsis circadian clock component LHY

Abstract

In the model plant Arabidopsis thaliana, the circadian clock is believed to be composed of a number of coupled transcriptional negative feedback loops. The LATE ELONGATED HYPOCOTYL (LHY) gene is thought to form part of at least two of these transcriptional feedback loops, as well as playing a role in the perception of light signals by the clock. To better understand how multiple transcriptional feedback loops might be integrated in the transcriptional regulation of LHY, we have performed an analysis of the cis-regulation of this gene. Through deletion analysis of reporter gene constructs, we have identified a 957 basepair region of the LHY promoter which contains sufficient sequence to direct the characteristic expression profile of LHY. Furthermore, we provide evidence that at least two circadian signals converge on this region. Electrophoretic mobility shift assays identified four classes of candidate cis-elements within the LHY promoter including a poly-CTT tract, an AAAAA motif, a candidate MYB-binding site and a G-box motif. Through mutational analysis of these elements, we have been able to determine aspects of their in vivo regulatory function. We report that a G-box motif and the previously uncharacterized AAAAA element are implicated in the regulation of LHY transcription by light signals. In etiolated seedlings, the region of the LHY promoter containing the MYB-binding site motif and multiple copies of the poly-CTT motif mediates regulation of LHY by both light-responsive and circadian signals