Integrative Analysis of DNA Methylome and Transcriptome Reveals the Mechanism of Heat Tolerance in Non-heading Chinese Cabbage

Heat stress profoundly affects the growth and development of non-heading Chinese cabbage (NHCC) and usually results in great losses in yield and quality. In this study, we observed a significant increase in CHH methylation, specifically within gene promoter regions, in NHCC upon heat stress exposure. Furthermore, application of DNA methylation inhibitor 5-azacytidine was found to significantly exacerbating heat stress-induced NHCC wilting. Integrative analysis of DNA methylome and transcriptome identified several heat stress-inhibited regulators, such as IQD21, SMR1, and PCR2, which negatively regulates the heat tolerance, and silencing these genes significantly enhanced the heat tolerance of NHCC. Our findings demonstrated that heat stress triggers hypermethylation of CHH within promoters of some negative heat stress regulators, thus improving the heat adaptation of NHCC. These findings provide new insights into the mechanism of NHCC adapting to heat stress and suggest a crucial role of DNA methylation in regulating the heat tolerance of NHCC.