Revalidation of the ICE1–CBF Regulatory Model in Arabidopsis Cold Stress Response

Plants encountering cold stress undergo physiological adaptations crucial for acquiring freezing tolerance, involving the transcriptional activation of genes encoding C-repeat binding factors (CBFs). Inducer of CBF expression 1 (ICE1) has long been acknowledged as a master regulator in the cold response, positively modulating the expression of cold-inducible CBF genes. However, recent studies that ICE1 is not involved in the regulation of CBF genes have challenged this established notion, prompting a critical reevaluation of the ICE1-CBF regulatory model. To address this controversy, ice1-2 mutants were germinated on media containing 1% glucose and grown under short periodic conditions, ensuring comparable growth to wild-type (WT) plants before cold treatment. Surprisingly, our modified growth conditions revealed no discernible differences in the cold induction of CBF genes and their downstream targets between WT plants and ice1-2 mutants. Moreover, cold-induced degradation of ICE1, mediated by the E3 ubiquitin ligase high expression of osmotically-responsive genes 1 (HOS1), was notably absent in two different ICE1 transgenic plants. Consistent with this, cold-responsive gene expression profiling showed no difference between WT plants and hos1 mutants. All our data strongly suggest that the HOS1-ICE1 regulatory module does not play a role in the cold regulation of the CBF signaling pathway in Arabidopsis.