Origin and evolution of tetraploid species in genus elymus

麦草属与小麦、大麦和黑麦属于同一类群。这一属的禾本科植物已经适应了各种气候和栖息地，使它们成为谷物和饲料育种的宝贵遗传资源，也是进化、分类学和物种形成研究的优秀群体。所有的小麦草都由至少两组不同的染色体组成，其中大多数品种都有StY和StH染色体组合。有StH组合的物种约有50种。其中St基因组来自于原属Pseudoroegneria， H基因组来自于野生大麦。关于这一群体的一个争论是，不同的StH物种是由一对亲本、一种Pseudoroegneria物种和一种野生大麦之间的古代杂交产生的，然后分化成多个物种（单一起源），还是不同的StH物种是由不同时间和地点的不同对亲本杂交产生的（多重起源）。我们将测试羊草的St和H基因组是否具有多个起源。有一种假说认为，同种异体多倍体的物种可能起源于自多倍体（StStStSt），在多倍体物种中，相同的基因组逐渐分化，导致了今天的同种异体四倍体的物种。我们的rpb2数据不支持St和Y基因组在StY物种中的相同起源。利用其他基因对其进行系统发育分析，将检验其是否为异源多倍体。我的研究将旨在测试StH物种中的St和H染色体组是否具有多个起源，并表征细胞遗传学上不同的StH和StY物种之间的差异。最后，我将测试Y基因组物种是同种还是自多倍体起源，并检查Y基因组与小麦科其他基因组的遗传关系。

Wheatgrass genus Elymus is within the same group as wheat, barley and rye. Grasses within this genus have adapted to various climates and habitats, making them valuable genetic resources for cereal and forage breeding as well as an excellent group for research in evolution, taxonomy, and speciation. All wheatgrasses are made up of at least two different sets of chromosomes with most species having the StY and StH chromosome combination. There are about 50 species with StH combination. The St genome comes from ancestor species in genus Pseudoroegneria and H from wild barley. One debate on this group has been whether different StH species arose by an ancient cross between the one pair of parents, a Pseudoroegneria species and a wild barley and then differentiated into a number of species (single origin), or different StH species arose by crosses between different pairs of the parents at different times and places (multiple origins). We will test whether the St and H genomes in Elymus are of multiple origins. It has been hypothesized that allopolyploid StY species may have an origin from autopolyploid (StStStSt) and the same genome differentiated gradually within the polyploid species resulting in today's StY genome allotetraploid Elymus. Our rpb2 data did not support the same origin of St and Y genome in StY species. Phylogenetic analysis of the StY species usig other genes will test whether StY species are allopolyploid origin. My study will be designed to test whether the St and H haplomes in StH species are of multiple origins, and characterize differences between cytogenetically distinct StH and StY species. Lastly, I shall test if StY genome species is allo- or autopolyploid origin and examine genetic relationships of the Y genome to other genomes in Triticeae.