Reciprocal regulation between TOC1 and LHY/CCA1 within the Arabidopsis circadian clock

The interactive regulation between clock genes is central for oscillator fu nction. Here, we show interactions between the Arabidopsis clock genes LATE ELONGATED HYPOCOTYL (LHY), CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), and TIMING OF CAB EXPRESSION 1 (TOC1). The MYB transcription factors LHY and CCA1 neg atively regulate TOC1 expression. We show that both proteins bind to a regi on in the TOC1 promoter that is critical for its clock regulation. Converse ly, TOC1 appears to participate in the positive regulation of LHY and CCA1 expression. Our results indicate that these interactions form a loop critic al for clock function in Arabidopsis.