三种重要披碱草属植物适应海拔变化的种群遗传学证据

In nature, Elymus species show the high adaptability to the altitude by hybridization, introgression and geographical differentiation as the important evolutionary processes. Tetraploid Elymus burchan-buddae (StY), E. sibiricus (StH) and hexaploid E. nutans (StHY) are studied because of their similar morphology, different genome constitution and overlapping habitat. Based on the former research background, we provide some scientific problems: (1) do the similar hybridization and differentiation processes exist between three Elymus species? (2) what genetic mechanism lead to the wide distribution of them along the altitude? (3) in addition to the hypothesis of the same origin between Y and St genomes, is there a probability of the same origin between Y and H genomes? In order to test the hypotheses above, gene sequencing method for the macroevolution and genetic markers for the microevolution will be applied in three important Elymus species to focus on the gene flow among different taxa and evolutionary relationship at various altitudes. Finally, we will explore the formation process (microevolution) of population genetic character along the altitude based on the hybridization-differentiation events (macroevolution) and provide the population genetic evidences for interspecific hybridization and genomic adaptation evolution of Elymus species.

披碱草属植物对海拔表现较强的适应性，杂交渐渗和地理分化是其重要的进化途径。在多年研究的基础上提出科学问题：三种形态特征相似、基因组构成不同、地理分布区域重叠的披碱草属植物：四倍体昆仑披碱草（Elymus burchan-buddae，StY）、老芒麦（E. sibiricus，StH）和六倍体垂穗披碱草（E. nutans，StHY）在海拔梯度上是否存在相似的杂交-分化过程？三者在多种海拔广泛分布需要什么样的遗传机制来维持？除了Y与St基因组有共同起源的假说，是否也有Y和H有共同的起源（祖先）的可能？为了验证上述假设，本项目综合采用研究宏进化的基因序列和微进化的分子标记，基于基因序列反映的杂交-分化（宏进化）事件，紧紧围绕不同海拔类群间的基因流和进化关系，重点研究不同海拔种群遗传特征的形成过程（微进化），以期为披碱草属植物的种间杂交和基因组适应性进化提供种群遗传学证据。

针对青藏高原广泛分布的披碱草属植物资源丰富且保护利用缺乏种群遗传学理论基础，以及披碱草属植物系统发育和进化关系复杂等问题，项目开展了不同海拔三种披碱草属植物形态特征、种内种间基因组大小变异分析、基因组原位杂交、多基因序列揭示的系统发育关系和不同海拔高度披碱草的种群遗传结构及异交率测定等研究，表型数据表明四倍体披碱草属植物对海拔的变化反应更加敏感；垂穗披碱草、老芒麦和昆仑披碱草基因组大小分别为9.54，8.29和6.10 Gb，披碱草的基因组大小在中海拔(3400-3700m)变化较大；基于ITS和Waxy序列海拔系统发育关系支持中等海拔起源假说；在杂交-分化过程中，海拔起到了重要的推动作用，而且中等基因组高度分化；St和Y基因组之间的同源性低于St和H基因组，与St和Y基因组之间的关系相比，H和Y基因组更近；低海拔异交率值最高，其次是中海拔，种子和花粉均是构成基因流的重要因素。这些研究结果对研究青藏高原异源多倍体披碱草属植物基因组进化具有重要的科学价值，在一定程度上揭示了披碱草属植物对青藏高原海拔变化的高度适应性及对其种质资源的保护和利用具有积极作用。