野生稻生态适应基因SK2的自然变异及进化意义

The evolution of ecological adaptation in closely related species is a key component of ecological adaptation.Reconstructing the evolutionary process of population adaptation is fundamental to understanding the mechanisms by which a population adapts to its environment and ultimately the process of speciation. Ecological adaptation between populations is driven by divergent natural selection between contrasting environments, resulting in ecological speciation through the evolution of reproductive isolation. However, in most examples of ecological adaptation the mechanistic basis of ecological divergence remains unclear,especially in plants. Two closely related Oryza spcies (Oryza rufipogon and Oryza nivara) are more closely related and collectively regarded as the progenitors of Oryza sativa. Multiple lines of evidence showed that O. nivara was derived from O. rufipogon populations quite recently (about 0.16 million years ago) to associate with an ecological shift from persistently wet to seasonally dry habitat. The molecular basis of the two wild rices divergence is SK2 locus. In the present program, we are going to determine natural variation,expression patter and evolutionary signal of SK2 and downstream EXPB12 genes by collecting multiple natural populations,accessions across the entire gergraphic ranges of the two species. We take advantage of the population samples collected from sympatric O.rufipogon and O.nivara populations to carry out apopulation genetic analysis on the two genes.Our major objectives were: (i) to comparatively investigate the nucleotide diversity of SK2 and EXPB12 for the two species at both coding and regulatory regions; (ii) to reveal the possible roles of natural selection on divergence and adaptation of O.rufipogon and O.nivara. Answers to these questions would help gain further insights into the origin and divergence of these wild rice species and the understanding of plant adaptation and speciation in general.

生态适应在植物新物种形成过程中扮演着重要的角色，由于生境差异而发生的生态适应受异质环境下不同的自然选择所驱动。植物类群中生态适应的机制及其遗传基础仍很不清楚。水稻的两个濒危野生类群（O.rufipogon,O.nivara）是新近分化的研究生态适应的理想模式，其对水生境的适应性受SK2控制。在自然条件下对SK2基因的变异模式、表达规律及基因受到的自然选择，所知甚少。本项目利用这两种野生稻分布区内的多个代表性天然群体及野生个体材料， 比较SK2及处于SK2信号下游的EXPB12位点在编码区、调控区及上下游区的多样性，检测基因表达模式、等位基因功能分化模式、两个基因的自然选择信号及连锁不平衡，追溯SK2基因多样性的来源、功能分化模式及进化历史；同时，用不同地区的多个邻域生长的O. rufipogon/O. nivara群体对，验证O.nivara是一次还是多次起源于O.rufipogon。

在植物演化及物种形成过程中，生态适应都扮演着重要角色，而植物类群中生态适应的机制及其遗传基础还不清楚。本课题以水稻新近分化的两个野生类群(O. rufipogon,O. nivara)为研究对象，对其控制水生境适应性的 SK2 基因的DNA变异模式、基因表达式样及受到的自然选择类型进行了研究。我们充分选取了两种野生稻分布区内的多个代表性的天然群体材料，完成了野生稻材料的筛选、转录组数据分析和群体水平的基因组序列分析工作，以追溯SK2基因多样性的来源、功能分化模式及进化历史。同时，还基于不同分布地的多个邻域生长的群体对，分析了O. nivara的起源方式。