Integrated Physiological and Transcriptomic Analysis Reveals Key Transcriptional Responses to Prolonged Heat Stress in Chinese Cabbage

Heat stress severely impairs plant growth and productivity, particularly in cool-season crops such as Chinese cabbage (Brassica rapa subsp. pekinensis). While short-term heat responses have been extensively studied, the mechanisms underlying prolonged heat stress adaptation remain insufficiently understood. In this study, we conducted an integrative analysis of Chinese cabbage exposed to sustained high temperatures. Our approach combined physiological characterization, antioxidant profiling, and transcriptome-wide gene expression analysis to dissect long-term heat stress responses. Prolonged heat stress caused marked growth inhibition, including leaf chlorosis and a 39% reduction in leaf length by day 9. Biochemical analyses revealed a progressive accumulation of ROS, indicated by elevated MDA content, while increased SOD and APX activities reflected active antioxidant responses. Transcriptome analysis identified over 10,000 DEGs at both 2 and 5 days, reflecting dynamic transcriptional reprogramming. GO and KEGG enrichment highlighted a temporal shift from RNA modification to protein synthesis pathways. Six transcription factors, including BrHSF B-1, BrNAC13, and BrbZIP43, were strongly induced, suggesting roles as early and persistent stress responders. Together, our findings offer a comprehensive, time-resolved view of B. rapa responses to prolonged heat stress and offer potential molecular targets for enhancing thermotolerance in Brassica breeding programs.