Molecular characterization and transcription analysis of DNA methyltransferase genes in tomato (Solanum lycopersicum)

DNA methylation plays an important role in plant growth and development, gene expression regulation, and maintenance of genome stability. However, only little information regarding stress-related DNA methyltransferases (MTases) genes is available in tomato. Here, we report the analysis of nine tomato MTases, which were categorized into four known subfamilies. Structural analysis suggested their DNA methylase domains are highly conserved, whereas the N-terminals are divergent. Tissue-specific analysis of these MTase genes revealed that SlCMT2, SlCMT3, and SlDRM5 were expressed higher in young leaves, while SlMET1, SlCMT4, SlDRM7, and SlDRM8 were highly expressed in immature green fruit, and their expression declined continuously with further fruit development. In contrast, SlMETL was highly expressed in ripening fruit and displayed an up-regulated tendency during fruit development. In addition, the expression of SlMET1 in the ripening of mutant rin and Nr tomatoes is significantly higher compared to wild-type tomato, suggesting that SlMET1 was negatively regulated by the ethylene signal and ripening regulator MADS-RIN. Furthermore, expression analysis under abiotic stresses revealed that these MTase genes were stress-responsive and may function diversely in different stress conditions. Overall, our results provide valuable information for exploring the regulation of tomato fruit ripening and response to abiotic stress through DNA methylation.