DNA methylation alterations of rice in response to cold stress

Rice is sensitive to cold stress, and cold tolerance in rice is a complex trait. In the present study, DNA methylation alterations induced by cold stress were examined in two contrasting rice genotypes, Li-Jiang-Xin-Tuan-Hei-Gu (LTH) and IR64, by methylation-sensitive amplified polymorphism analysis. At the seedling stage, a remarkable increase in DNA methylation under cold stress was detected only in the roots of the cold-tolerant genotype of LTH. Demethylation in the panicles of LTH under cold stress and subsequent recovery were determined. An increase in DNA methylation in the leaves and demethylation in the panicles were observed in IR64 at the booting stage under cold stress. These results indicate that cold-induced DNA methylation alterations are specific to genotypes and are dependent on the growth stage and tissue/organ types. Further analysis suggests that a number of cold-induced DNA methylation changes in both genotypes cannot be reverted after recovery, implying that these loci with alterations of DNA methylation may be mitotically heritable and involved in cold stress responsiveness.