Department of Vegetable Science, College of Horticulture, China Agricultural University, Beijing, P.R. China.
Beijing Key Laboratory of Growth and Developmental Regulation for Protected Vegetable Crops, Department of Vegetable Science, College of Horticulture, China Agricultural University, Beijing, P.R. China.
J Exp Bot. 2020 Mar 25;71(6):1928-1942. doi: 10.1093/jxb/eraa003.
There is growing evidence to suggest that epigenetic tags, especially DNA methylation, are critical regulators of fruit ripening. To examine whether this is the case in sweet pepper (Capsicum annuum) we conducted experiments at the transcriptional, epigenetic, and physiological levels. McrBC PCR, bisulfite sequencing, and real-time PCR demonstrated that DNA hypomethylation occurred in the upstream region of the transcription start site of some genes related to pepper ripening at the turning stage, which may be attributed to up-regulation of CaDML2-like and down-regulation of CaMET1-like1, CaMET1-like2, CaCMT2-like, and CaCMT4-like. Silencing of CaMET1-like1 by virus-induced gene silencing led to DNA hypomethylation, increased content of soluble solids, and accumulation of carotenoids in the fruit, which was accompanied by changes in expression of genes involved in capsanthin/capsorubin biosynthesis, cell wall degradation, and phytohormone metabolism and signaling. Endogenous ABA increased during fruit ripening, whereas endogenous IAA showed an opposite trend. No ethylene signal was detected during ripening. DNA hypomethylation repressed the expression of auxin and gibberellin biosynthesis genes as well as cytokinin degradation genes, but induced the expression of ABA biosynthesis genes. In mature-green pericarp, exogenous ABA induced expression of CaDML2-like but repressed that of CaCMT4-like. IAA treatment promoted the transcription of CaMET1-like1 and CaCMT3-like. Ethephon significantly up-regulated the expression of CaDML2-like. Treatment with GA3 and 6-BA showed indistinct effects on DNA methylation at the transcriptional level. On the basis of the results, a model is proposed that suggests a high likelihood of a role for DNA methylation in the regulation of ripening in the non-climacteric pepper fruit.
越来越多的证据表明，表观遗传标记，尤其是 DNA 甲基化，是果实成熟的关键调控因子。为了研究这是否适用于甜椒（Capsicum annuum），我们在转录、表观遗传和生理水平上进行了实验。McrBC PCR、亚硫酸氢盐测序和实时 PCR 表明，在转色期一些与辣椒成熟相关基因的转录起始位点上游区域发生了 DNA 低甲基化，这可能归因于 CaDML2-like 的上调和 CaMET1-like1、CaMET1-like2、CaCMT2-like 和 CaCMT4-like 的下调。通过病毒诱导的基因沉默沉默 CaMET1-like1 导致 DNA 低甲基化，增加了果实中可溶性固形物的含量和类胡萝卜素的积累，同时伴随着参与辣椒素/辣椒红素生物合成、细胞壁降解和植物激素代谢和信号转导的基因表达的变化。ABA 在内源果实成熟过程中增加，而 IAA 则呈现相反的趋势。在成熟过程中未检测到乙烯信号。DNA 低甲基化抑制了生长素和赤霉素生物合成基因以及细胞分裂素降解基因的表达，但诱导了 ABA 生物合成基因的表达。在成熟绿色的果皮中，外源 ABA 诱导 CaDML2-like 的表达，但抑制 CaCMT4-like 的表达。IAA 处理促进了 CaMET1-like1 和 CaCMT3-like 的转录。乙烯利显著上调 CaDML2-like 的表达。GA3 和 6-BA 的处理对转录水平的 DNA 甲基化没有明显影响。基于这些结果，提出了一个模型，表明 DNA 甲基化在非跃变型辣椒果实成熟调控中很可能起作用。
