油菜SDG8基因中新发现VHE基序的功能研究

One of the main biological functions of histone lysine methyl transferase SDG8 gene is to control flowering, but it is still unknown how to regulate the time of flowering. The Arabidopsis SDG8, with a variety of physiological functions, has four known functional domains close to its C-terminal. But the function of its more than 350 amino acid residues N-terminal is still unknown. The full-length CDS of the SDG8 genes had been cloned from Brassica rapa, Brassica oleracea and Brassica napus, respectively. During the SNP primer-designing progress, we occasionally found that, in the function-unknown more than 350 amino acids sequence, there is a conserved protein domain, consisting of 39 amino acids, temporarily named VHE domain. What’s more, there are two successive VHE domains in the SDG8 protein of Brassica oleracea, and only one in the SDG8 proteins of Brassica rapa and Arabidopsis. According to statistical flowering time after the winter, Brassica rapa boltings earlier than Brassica napus and Brassica napus boltings earlier than Brasicca oleracea. Combining the bioinformatics analysis, by.which we found that the VHE domain only exits in the protein SDG8 involved in flowering control, and statistical analysis of the time to bolting in the three species of rape, we infered that the new VHE domain is likely to be associated with the time to bolting of plants in Cruciferae. Therefor, by dint of the epigenetics, molecular biology techniques and so on, this project aim is to uncover the function of the novel VHE domain of the SDG8 proteins, which will have positive significance for deeply insight of the epigenetic regultion mechnism of flowering in Brassicaceae.

组蛋白赖氨酸甲基转移酶SDG8基因参与植物春化途径的开花调控，但是它如何调节开花期的早晚还是一个未知。我们在研究白菜、甘蓝和甘蓝型油菜三个物种SDG8基因的过程中，偶然发现在SDG8的N端未知功能区，存在一段由39个氨基酸残基组成的保守序列（暂命名为VHE基序）；且白菜BraSDG8中只有1个VHE；甘蓝BolSDG8中有2个连续的VHE；甘蓝型油菜A/C组的SDG8分别含1个和2个VHE。进一步分析发现VHE只存在于十字花科的SDG8中；而SDG8参与春化途径的开花调控，相同条件下，越冬后三种油菜的开花期为白菜早于甘蓝型油菜，甘蓝型油菜早于甘蓝。综合分析后，我们推测VHE的数量可能与SDG8调控植物进入开花期的早晚有关。为此，本项目拟通过表观遗传学、分子生物学等技术手段，揭示SDG8蛋白中新发现VHE的作用，这对人们深入认识春化条件下油菜花期形成的精细表观调控机制具有积极意义。

为了解决南方“稻-稻-油”种植模式过程中出现的接茬冲突这个实际问题，需要压缩油菜生长周期，为此必须选育早花早熟的油菜种质，而早花是早熟的前提。如何让油菜提早进入生殖生长，实现由营养生长转换到生殖生长，就需要对油菜感应春化的分子机制开展研究。以我们已有关于油菜花性转换研究为基础，通过本项目研究进一步揭示其油菜开花的表观遗传调控机制。具体对甘蓝型油菜组蛋白赖氨酸甲基化酶BnaSDG8.A/C以及其蛋白序列上新发现VHE结构域的数量与油菜花性转换早晚的关系开展研究，揭示油菜的春化受表观遗传调控。具体是BnaSDG8基因通过改变靶位点染色质组蛋白赖氨酸甲基化来调控油菜营养生长进入生殖生长；而BnaSDG8上的VHE结构域数量决定了目标位点染色质的甲基化程度，甲基化程度进而决定了油菜营养生长进入生殖生长的早晚。VHE是在SDG8蛋白上首次发现的新结构域，这次对VHE功能的阐释，为这动植物领域相关研究提供了重要参考价值。利用本项目研究成果，顺利指导了特早熟甘蓝型油菜GX72、GX73、GX74等系列品系的选育，为彻底解决“稻-稻-油”接茬冲突提供了可靠种植资源。这成为理论研究成果指导油菜育种实践的典型范例。