Posttranslational regulation of multiple clock-related transcription factors triggers cold-inducible gene expression in <i>Arabidopsis</i>.

Abstract

Cold stress is an adverse environmental condition that affects plant growth, development, and crop productivity. Under cold stress conditions, the expression of numerous genes that function in the stress response and tolerance is induced in various plant species, and the dehydration-responsive element (DRE) binding protein 1/C-repeat binding factor (DREB1/CBF) transcription factors function as master switches for cold-inducible gene expression. Cold stress strongly induces these <i>DREB1</i> genes. Therefore, it is important to elucidate the mechanisms of <i>DREB1</i> expression in response to cold stress to clarify the perception and response of cold stress in plants. Previous studies indicated that the central oscillator components of the circadian clock, CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY), are involved in cold-inducible <i>DREB1</i> expression, but the underlying mechanisms are not clear. We revealed that the clock-related MYB proteins REVEILLE4/LHY-CCA1-Like1 (RVE4/LCL1) and RVE8/LCL5 are quickly and reversibly transferred from the cytoplasm to the nucleus under cold stress conditions and function as direct transcriptional activators of <i>DREB1</i> expression. We found that CCA1 and LHY suppressed the expression of <i>DREB1s</i> under unstressed conditions and were rapidly degraded specifically in response to cold stress, which suggests that they act as transcriptional repressors and indirectly regulate the cold-inducible expression of <i>DREB1s</i> We concluded that posttranslational regulation of multiple clock-related transcription factors triggers cold-inducible gene expression. Our findings clarify the complex relationship between the plant circadian clock and the regulatory mechanisms of cold-inducible gene expression.