组蛋白H3K9甲基化修饰调控玉米果穗不同部位种子活力差异的机理研究

Seed vigor is an important index of evaluating seed quality, and high seed vigor is the key factor to ensure full stand and strong seedlings. In this study, we use the maize seeds located on different position on the ear as the materials, which have different seed vigor generated during seeds developing. From comparative transcriptome data of middle vs top part seeds of the maize ear, we selected five differentially expressed putative histone H3K9 methyltransferase genes as objects of study. By this study, we want to explore the mechanism underlying variability of seed vigor of maize seeds located on different position on the ear regulated by histone H3K9 methylation. Firstly, based on whether the three kinds of H3K9 methylation and the expression pattern of target genes are regulated by ABA or GA, also combing with H3K9 methyltransferase activity in vitro, we will screen for one or two putative histone H3K9 methylase gene(s) in this study. Then, we will explore the effects of selected gene(s) on seed vigor and H3K9 methylation of seeds located on different position on the ear, through over-expression transgenic lines and UniformMu mutants. Lastly, we will explore the genomic location of the differentiated H3K9 methylation of wild type, over-expression lines and UniformMu mutants by ChIP-seq, identify its target genes, and illuminate mechanisms underlying variability of seed vigor of maize seeds located on different position on the ear, regulated by histone H3K9 methylation. The present project has not only theoretical importance but also practice guidance to producing and processing of seeds with high vigor.

种子活力是衡量种子播种质量的重要指标，选用高活力种子是实现一播全苗、苗强苗壮的重要保障。本研究以玉米果穗不同部位活力不同的种子为材料，以前期研究发现的果穗中部/上部种子5个差异表达假定组蛋白H3K9甲基转移酶基因为研究对象，探讨组蛋白H3K9甲基化修饰调控玉米果穗不同部位种子活力差异的机理。首先根据3种H3K9甲基化修饰和目的基因表达模式受ABA、GA调控情况以及体外H3K9甲基转移酶活性，从5个假定H3K9甲基转移酶基因中筛选1-2个基因；然后通过转基因和突变体材料研究被选择基因过表达和低表达对果穗不同部位种子活力和H3K9甲基化修饰的影响；最后通过ChIP-seq技术研究野生型以及目标基因过表达和低表达玉米种子差异H3K9甲基化修饰所在基因组区域，发现其修饰基因，进而阐明H3K9甲基化修饰调控种子活力的机理。本研究对于高活力种子生产和种子精选分级具有重要的理论指导意义和潜在的应用价值。

同一植株或同一果穗不同部位着生的种子往往活力不同，因此，未分级的种子通常出苗不整齐，给作物生产造成不利影响。前期研究发现组蛋白H3K9甲基化修饰可能在玉米果穗不同部位种子活力差异中具有重要作用，本项目通过组学与分子生物学相结合的方法，研究H3K9甲基化修饰调控玉米果穗不同部位种子活力差异的机理。本项目首先通过ABA合成抑制剂氟啶酮调控种子内源激素的水平，并研究激素对H3K9甲基化水平和组蛋白甲基转移酶基因表达水平的影响，筛选出重要的组蛋白甲基转移酶基因ZmSUVH2；然后通过转基因获得ZmSUVH2基因过表达材料，研究发现种子ZmSUVH2基因表达水平与H3K9me2水平呈正相关，与种子活力呈负相关；最后通过ZmSUVH2基因不同表达水平的材料进行ChIP-seq和RNA-seq分析，结果表明ZmSUVH2基因通过影响内质网内蛋白质加工、植物激素的信号转导以及影响种子碳氮代谢和能量合成调控种子的活力。研究成果为种子的精选加工提供理论依据。