Recent progress of molecular mechanisms of DNA methylation in plant response to abiotic stress

In order to survive in extreme environments, plants have evolved multiple mechanisms, such as DNA methylation, to adapt to environmental stress. A large number of investigations indicate that abiotic stress triggers changes in DNA methylation, resulting in fluctuations of expression levels of stress-related genes, thereby enhancing stress tolerance in plants. This review summarized that DNA methylation in plants can enhance tolerance to abiotic stress, including nutrient, sulfur dioxide (SO2), metal, temperature and osmotic stress. The dynamics of DNA methylation in plant under abiotic stress was discussed from the aspects of genome stability, gene expression, gene silencing and protein interaction. Moreover, several important pathways of methylation also are involved in response to stress. Firstly, methylation activated or inhibited gene expression and mediatted interaction of genes under abiotic stress. Secondly, the RNA-directed DNA methylation (RdDM) pathway can participate in gene expression. Third, up-regulation of DNA methylase and demethylase genes can also affect DNA methylation levels. Fourth, methylation mediated the response of plant antioxidant system. Fifth, DNA methylation had a potential regulatory role in plant cross-adaptation. Additionally, we summarized the methylation of abscisic acid and ethylene synthesis related-genes under stress. We also speculate that the interaction of methylation with other phytohormones can enhance plant stress resistance. Therefore, this review provides a better understanding of plant response to abiotic stress at the molecular level.