RESUMO
Transcriptional feedback loops are central to the architecture of eukaryotic circadian clocks. Models of the Arabidopsis thaliana circadian clock have emphasized transcriptional repressors, but recently, Myb-like REVEILLE (RVE) transcription factors have been established as transcriptional activators of central clock components, including PSEUDO-RESPONSE REGULATOR5 (PRR5) and TIMING OF CAB EXPRESSION1 (TOC1). We show here that NIGHT LIGHT-INDUCIBLE AND CLOCK-REGULATED1 (LNK1) and LNK2, members of a small family of four LNK proteins, dynamically interact with morning-expressed oscillator components, including RVE4 and RVE8. Mutational disruption of LNK1 and LNK2 function prevents transcriptional activation of PRR5 by RVE8. The LNKs lack known DNA binding domains, yet LNK1 acts as a transcriptional activator in yeast and in planta. Chromatin immunoprecipitation shows that LNK1 is recruited to the PRR5 and TOC1 promoters in planta. We conclude that LNK1 is a transcriptional coactivator necessary for expression of the clock genes PRR5 and TOC1 through recruitment to their promoters via interaction with bona fide DNA binding proteins such as RVE4 and RVE8.
Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Transativadores/genética , Arabidopsis/fisiologia , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis/metabolismo , Imunoprecipitação da Cromatina , Relógios Circadianos , Ritmo Circadiano , Flores/genética , Flores/fisiologia , Flores/efeitos da radiação , Genes Reporter , Luz , Modelos Genéticos , Mutação , Regiões Promotoras Genéticas/genética , Transativadores/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
Transcriptional feedback loops in Arabidopsis circadian clock is composed of more repressive components, while the knowledge of activation mechanism remains limited. We recently reported 2 members from a family of NIGHT LIGHT-INDUCIBLE AND CLOCK-REGULATED genes, LNK1 and LNK2, dynamically interact with morning-phased transcriptional factors, like CIRCADIAN CLOCK ASSOCIATED1 (CCA1), LATE ELONGATED HYPOCOTYL (LHY), REVEILLE8 (RVE8) and RVE4, and function as coactivators for the expression of TIMING OF CAB EXPRESSION1 (TOC1) and PSEUDO-RESPONSE REGULATOR5 (PRR5) via transcriptional factors RVE8 and RVE4. Here we provide evidence that both LNK1 and LNK2 play critical role in the transcriptional activation of PRR5, LNK1 may contribute more than LNK2 did under experimental conditions. We also identified that both LNK1 and LNK2 recruitment to the evening element of PRR5 promoter via LNK1-RVE8 or LNK2-RVE8 proteins complex through electrophoretic mobility shift assay. Therefore LNK1 and LNK2 function as coactivator of dawn-phased MYB-like transcription factors, such as RVE8 in morning complex to regulate the target genes expression.