Abstract

Up to 30 % of the plant transcriptome is circadian regulated in different species. However, we still lack a good understanding of the mechanisms involved in these genome-wide oscillations in gene expression. Here we show that PSEUDO -RESPONSE REGULATOR 7 (PRR7), a central component of the Arabidopsis clock, is directly involved in the repression of master regulators of plant growth, light signaling and stress responses. PRR7 forms a feedback loop with CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) to regulate circadian rhythms. By combining chromatin immunoprecipitation with next generation sequencing we could confirm the direct regulation of CCA1 and LHY by PRR7 in addition to identifying the genome-wide targets of PRR7 . The expression levels of most PRR7 target genes peak around dawn, in an antiphasic manner to PRR7 protein levels and were repressed by PRR7 . These findings indicate that PRR7 is important for cyclic gene expression by repressing the transcription of morning-expressed genes. Furthermore, using simple mathematical models we hypothesized that the differences in the phase of expression of PRR7 target genes could be due to a combinatorial regulation with other cyclic factors. Using chromatin immunoprecipitation and expression analysis we could show that indeed several PRR7 targets are directly regulated by other clock components in addition to PRR7 .