अमूर्त

Cold acclimation alters DNA Methylation patterns in Brassica - rapa and confers tolerance to heat and high Growth rate

Tongkun Liu

Epigenetic modifications are implicated in plant adaptations to abiotic stresses. Exposure of plants to one stress induces resistance to other stresses, which is called cross-adaptation and is not well understood. In this study, we aimed to unravel the epigenetic basis of elevated heat-tolerance in cold-acclimated Brassica rapa by genome-wide DNA methylation analysis of leaves from Control (CK) and Cold-Acclimated (CA) plants. We found both methylation and demethylation occurred during cold acclimation. Moreover, two significantly altered pathways, malate dehydrogenase activity and carbon fixation and 1,562 differentially methylated genes, including BramMDH1, BraKAT2, BraSHM4 and Bra4CL2 were identified in CA. Genetic validation and treatment of B. rapa with 5-aza-2-deoxycytidine (Aza) suggested promoter demethylation of four candidate genes increased their transcriptional activities. Physiological analysis suggested elevated heat-tolerance and high growth rate were closely related to increases in organic acids and photosynthesis, respectively. Functional analyses demonstrated that the candidate gene BramMDH1 (mMDH-mitochondrial Malate Dehydrogenase) directly enhances organic acids and photosynthesis to increase heat-tolerance and growth rate in Arabidopsis. However, Aza-treated B. rapa, which also has elevated BramMDH1 levels, did not exhibit enhanced heat-tolerance. We therefore suggest DNA demethylation alone is not sufficient to increase heat-tolerance. This study demonstrates that altered DNA methylation contributes to cross-adaptation.