Kong Weilong, Zhu Qiufang, Zhang Qing, Zhu Yiwang, Yang Jingjing, Chai Kun, Lei Wenlong, Jiang Mengwei, Zhang Shengcheng, Lin Jinke, Zhang Xingtan
National Key Laboratory for Tropical Crop Breeding, Shenzhen Branch, Guangdong Laboratory for Lingnan Modern Agriculture, Genome Analysis Laboratory of the Ministry of Agriculture, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen, Guangzhou 518120, China.
College of Horticulture, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China.
Hortic Res. 2023 Jun 13;10(8):uhad126. doi: 10.1093/hr/uhad126. eCollection 2023 Aug.
In plants, 5mC DNA methylation is an important and conserved epistatic mark involving genomic stability, gene transcriptional regulation, developmental regulation, abiotic stress response, metabolite synthesis, etc. However, the roles of 5mC DNA methylation modification (5mC methylation) in tea plant growth and development (in pre-harvest processing) and flavor substance synthesis in pre- and post-harvest processing are unknown. We therefore conducted a comprehensive methylation analysis of four key pre-harvest tissues (root, leaf, flower, and fruit) and two processed leaves during oolong tea post-harvest processing. We found that differential 5mC methylation among four key tissues is closely related to tissue functional differentiation and that genes expressed tissue-specifically, responsible for tissue-specific functions, maintain relatively low 5mC methylation levels relative to non-tissue-specifically expressed genes. Importantly, hypomethylation modifications of and / genes in roots provided the molecular basis for the dominant synthesis of theanine in roots. In addition, integration of 5mC DNA methylationomics, metabolomics, and transcriptomics of post-harvest leaves revealed that content changes in flavor metabolites during oolong tea processing were closely associated with transcription level changes in corresponding metabolite synthesis genes, and changes in transcript levels of these important synthesis genes were strictly regulated by 5mC methylation. We further report that some key genes during processing are regulated by 5mC methylation, which can effectively explain the content changes of important aroma metabolites, including α-farnesene, nerolidol, lipids, and taste substances such as catechins. Our results not only highlight the key roles of 5mC methylation in important flavor substance synthesis in pre- and post-harvest processing, but also provide epimutation-related gene targets for future improvement of tea quality or breeding of whole-tissue high-theanine varieties.
在植物中，5-甲基胞嘧啶（5mC）DNA甲基化是一种重要且保守的上位性标记，涉及基因组稳定性、基因转录调控、发育调控、非生物胁迫响应、代谢物合成等。然而，5mC DNA甲基化修饰（5mC甲基化）在茶树生长发育（采前加工）以及采前和采后加工中风味物质合成方面的作用尚不清楚。因此，我们对乌龙茶采后加工过程中的四个关键采前组织（根、叶、花和果实）以及两片加工叶进行了全面的甲基化分析。我们发现，四个关键组织之间的差异5mC甲基化与组织功能分化密切相关，负责组织特异性功能的组织特异性表达基因相对于非组织特异性表达基因维持相对较低的5mC甲基化水平。重要的是，根中 和 / 基因的低甲基化修饰为根中茶氨酸的优势合成提供了分子基础。此外，采后叶片的5mC DNA甲基化组学、代谢组学和转录组学整合分析表明，乌龙茶加工过程中风味代谢物含量的变化与相应代谢物合成基因的转录水平变化密切相关，这些重要合成基因的转录水平变化受到5mC甲基化的严格调控。我们进一步报道，加工过程中的一些关键基因受到5mC甲基化的调控，这可以有效解释包括α-法尼烯、橙花叔醇、脂质等重要香气代谢物以及儿茶素等滋味物质的含量变化。我们的研究结果不仅突出了5mC甲基化在采前和采后加工中重要风味物质合成中的关键作用，还为未来茶叶品质改良或全组织高茶氨酸品种选育提供了与表观突变相关的基因靶点。
