Minisymposium 16: Clocks & Light

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Abs # M1603: A CCA1-interacting RNA-binding protein (CIRP) functions in Arabidopsis circadian clock

Presenter:	Lu, Sheen X       Contact Presenter
Authors	Lu, Sheen X (A)   Daniel, Xavier  (B)   Tobin, Elaine M (A)
Affiliations:	(A): Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles (B): LIPM, UMR CNRS/INRA, France

Circadian rhythms are endogenous rhythms that help keep organisms in synchrony with their environment and contribute to an organism's fitness for life on earth. Most organisms share conserved mechanism of circadian rhythmicity, a central oscillator based on transcriptional negative feedback loops. In Arabidopsis, three proteins have been suggested as components of the oscillator: CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), LATE ELONGATED HYPOCOTYL (LHY), and TIMING OF CAB EXPRESSION 1 (TOC1). CCA1 and LHY negatively regulate TOC1 expression, and TOC1 is proposed to participate in the positive regulation of LHY and CCA1 expression. CCA1 encodes a highly conserved single-MYB domain transcription factor. Expression of CCA1 oscillates with a circadian rhythm. Constitutive expression of CCA1 not only suppresses its own expression, but also causes arrythmicity in gene expression, leaf movement, and hypocotyl elongation. To further investigate the role that CCA1 plays in the Arabidopsis clock, we have identified a putative RNA-binding protein that we designate as CIRP in a yeast two-hybrid screen for proteins that can interact with CCA1. Preliminary results show that the cirp null mutant flowers earlier than wild type under both long-day and short-day growth conditions. The cirp mutant also has shorter periods for rhythms of all genes examined. These findings indicate that CIRP may function in the Arabidopsis circadian clock although the CIRP RNA does not itself show a circadian rhythm.