A Novel Factor Linking the Regulation of Pre-mRNA Splicing and Circadian Rhythms in Arabidopsis

GUSTAVO SCHLAEN; SOLEDAD PEREZ SANTANGELO; MARCELO YANOVSKY

Miami

Congreso; 13th Biennial Meeting Society for Research on Biological Rhythms; 2012

SRBR

Circadian clocks allow organisms to time biological processes to the most appropriate phases of the day . There is increasing evidence that propper environmental regulation of clock function involves alterations in alternative splicing (AS) of clock genes, but very little is known about the mechanisms linking AS and the clock . We have recently shown that defects in PRMT5, which transfers methyl groups to arginine residues present in histones and Sm spliceosomal proteins, impair circadian rhythms in Arabidopsis . This phenotype is caused, at least in part, by a strong alteration in alternative splicing of the core clock gene PRR9 . In mammals, lack of methylation of Sm proteins leads to severe defects in spliceosome assembly . To further explore the link between splicing and the clock in plants we analyzed the effect of mutations in homologues of genes that are known to regulate the assembly of Sm proteins into small nuclear ribonucleopreteins (snRNPs) . In vertebrates, assembly of spliceosomal snRNPs is mediated by the SMN complex, composed of the proteins SMN and Gemins2?8 . Mutations in SMN and GEMIN2 like genes in Arabidopsis caused developmental defects whose intensity depended on photoperiodic conditions . Developmental and physiological alterations included changes in leaf shape, petiole length and flowering time . In addition, gemin2, but not smn-like mutants displayed altered light regulated responses as well as circadian rhythms in leaf movement and gene expression . Moreover, genome-wide studies showed that GEMIN2 contributes to the regulation of only a subset of pre-mRNA splicing events, particularly those involving alternative splicing . Indeed, the circadian phenotype of gemin2 mutants is consistent with increased retention of intron 4 of the clock gene TOC1, an alternative splicing event that has recently been shown to be regulated by temperature changes . These results provide novel mechanisms linking the circadian network to the regulation of AS. Furthermore, they suggest that GEMIN2 regulation of alternative splicing of TOC1 could contribute to temperature adjustment of the plant circadian clock