A Role for PRMT5 in the Regulation of Light Signaling and Clock

SANCHEZ, S; HERNANDO, E; RUGNONE, M; CERDAN, P; YANOVSKY, MJ

San Destin, Florida

Congreso; Society for Research on Biological Rhythms 11th Biennial Meeting; 2008

SRBR

Interlocked transcriptional feed-back loops are the basis of circadian oscillations in many organisms. In Arabidopsis these loops involve the Myb transcription factors CCA1 and LHY, and the pseudo-response regulators (PRRs) TOC1, PRR3, PRR5, PRR7 and PRR9. Using a forward genetic approach and positional cloning, we identified protein arginine methyltransferase 5 (PRMT5) as a key regulator of clock function and light signaling. prmt5 mutants show increased period length of circadian rhythms and reduced photomorphogenic responses to red, far-red and blue light suggesting that PRMT5 mediates light regulation of the circadian clock. prmt5 mutants flower very late under long and short day conditions due to an enhanced expression of the MADS box transcription factor FLC. Although FLC has been shown to regulate clock function, flc mutation suppresses the late flowering phenotype of prmt5 mutants but has no effect on its circadian phenotype. PRMT5 methylates histone and non-histone proteins, and regulates transcription, RNA processing, and signal transduction in many eukaryotic organisms. To further understand the mechanisms of PRTM5 action in plants we compared the prmt5 transcriptome with that of wild type plants using Affymetrix microarrays. Many more genes showed increased than decreased expression, suggesting that PRMT5 acts as a transcriptional repressor. The gene showing the highest enhancement in expression was PRR9, a key component of the Arabidopsis circadian oscillator, whose expression is also acutely regulated by light. Thus, our results uncover a role for arginine methylation in clock regulation in Arabidopsis, presumably through the direct or indirect regulation of the PRR9 clock gene.