Methyl-Sensitive Amplification Polymorphism (MSAP) Analysis Provides Insights into the DNA Methylation Changes Underlying Adaptation to Low Temperature of Brassica rapa L.

Background: DNA methylation can change rapidly to regulate the expression of stress-responsive genes. Previous studies have shown that there are significant differences in the cold resistance of winter rapeseed (Brassica rapa L.) after being domesticated in different selection environments: however, little is known about the epigenetic regulatory mechanisms of its cold resistance formation. Methods: Four winter rapeseed materials (&lsquo:CT-2360&rsquo:, &lsquo:MXW-1&rsquo:, &lsquo:2018-FJT&rsquo:, and &lsquo:DT-7&rsquo:) domesticated in different environments were selected to analyze the DNA methylation level and pattern changes under low temperature using methylation-sensitive amplified polymorphism technology with 60 primer pairs. Results: A total of 18 pairs of primers with good polymorphism were screened, and 1426 clear bands were amplified, with 594 methylation sites, accounting for 41.65% of the total amplified bands. The total methylation ratios of the four materials were reduced after low-temperature treatment, in which the DNA methylation level of &lsquo:CT-2360&rsquo: was higher than that of the other three materials: the analysis of methylation patterns revealed that the degree of demethylation was higher than that of methylation in &lsquo:MXW-1&rsquo:, &lsquo:2018-FJT&rsquo:, and &lsquo:DT-7&rsquo:, which were 22.99%, 19.77%, and 24.35%, respectively, and that the methylation events in &lsquo:CT-2360&rsquo: were predominantly dominant at 22.95%. Fifty-three polymorphic methylated DNA fragments were randomly selected and further analyzed, and twenty-nine of the cloned fragments were homologous to genes with known functions. The candidate genes VQ22 and LOC103871127 verified the existence of different expressive patterns before and after low-temperature treatment. Conclusions: Our work implies the critical role of DNA methylation in the formation of cold resistance in winter rapeseed. These results provide a comprehensive insight into the adaptation epigenetic regulatory mechanism of Brassica rapa L. to low temperature, and the identified differentially methylated genes can also be used as important genetic resources for the multilateral breeding of winter-resistant varieties.