CIRCADIAN CLOCK ASSOCIATED 1 represses thermotolerance by inhibiting <i>HEAT SHOCK FACTOR A2</i> expression in nonheading Chinese cabbage

Abstract In the context of global warming, elevated temperatures present serious challenges to the growth, quality, and productivity of nonheading Chinese cabbage (NHCC). Understanding the mechanisms underlying thermotolerance in NHCCs is therefore critically important. In this study, we investigated the influence of heat stress (HS) duration and circadian rhythm on gene expression using time-resolved transcriptome sequencing. The results showed that during the early stages of HS, NHCC primarily engaged in physiological processes such as stimulus perception and signal transduction. In contrast, prolonged HS exposure activated antioxidant metabolism, reduced photosynthetic capacity, and accelerated leaf senescence. Weighted gene co-expression network analysis (WGCNA) further revealed a strong link between circadian regulation and HS responses. Notably, our findings demonstrate that the core circadian clock component CIRCADIAN CLOCK ASSOCIATED 1 (BcCCA1) negatively regulated heat tolerance by repressing the transcription of BcHSFA2. Collectively, these results provide new insights into the molecular mechanisms underlying HS responses in NHCCs and highlight the regulatory role of circadian rhythms in plant thermotolerance.