Transcriptome and Physiological Analysis of Heat and Chilling Stress Responses in Chinese Cabbage (Brassicarapa L. var. pekinensis)

Temperature stress impacts the quality and growth of Chinese cabbage. To evaluate resistance mechanisms of temperature stress in Chinese cabbage, the levels of oxidative stress response enzymes such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), as well as metabolites including proline, malondialdehyde (MDA), chlorophylls a and b were estimated. Under temperature stress, the contents of proline and MDA, along with the activities of SOD, POD and CAT increased significantly. Through transcriptome analysis, we found that 11 759 differentially expressed genes were highly enriched in metabolic pathways, which were concentrated on 'starch and sucrose metabolism' and 'plant hormone signal transduction'. Besides, spliceosome pathway was upregulated for heat stress adaptation, but no upregulation of the spliceosome pathway was observed during cold treatment. qRT-PCR validation and transcriptome analysis indicated that the genes of reactive oxygen species scavenging enzymes have different expression patterns under heat and cold stresses. BraA08g030930 (SOD-related), BraA01g040660 (POD-related), and BraA01g003280 (CAT-related) were significantly upregulated under heat stress, while BraA08g015510 (CAT-related) downregulated under cold stress. We found that the transcription factors of MYBs were the main family involved in heat and chilling stress response, and NACs (NAM, ATAF, and CUC transcription factors) actively responded to chilling stress. Our results reveal the changes in physiological parameters and gene expression patterns under heat and chilling stress, thereby providing valuable insights into elucidating the regulatory mechanisms of cold or heat tolerance in Chinese cabbage.