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

Abstract 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.

摘要 DNA甲基化在植物生长发育、基因表达调控及基因组稳定性维持中发挥关键作用。然而，目前番茄中与胁迫相关的DNA甲基转移酶（DNA methyltransferases, MTases）基因的相关研究信息仍较为有限。本研究对9个番茄DNA甲基转移酶基因进行系统分析，将其划分为4个已知亚家族。结构分析结果显示，这些基因的DNA甲基化酶结构域高度保守，而其N端序列则呈现显著分化。对这些甲基转移酶基因的组织特异性表达分析表明：SlCMT2、SlCMT3及SlDRM5在幼叶中表达量较高；SlMET1、SlCMT4、SlDRM7及SlDRM8在未成熟绿果中高表达，且其转录水平随果实进一步发育持续下调。与之相反，SlMETL在成熟果实中高表达，并在果实发育进程中呈现上调趋势。此外，在rin和Nr突变体番茄的成熟阶段，SlMET1的转录水平显著高于野生型番茄，这提示SlMET1受到乙烯信号及成熟调控因子MADS-RIN的负向调控。进一步的非生物胁迫表达分析显示，这些DNA甲基转移酶基因均具有胁迫响应特性，且在不同胁迫环境下可能发挥多样化的生物学功能。综上，本研究结果为解析通过DNA甲基化调控番茄果实成熟及响应非生物胁迫的分子机制提供了极具价值的参考依据。