Origin and evolution of tetraploid species in genus elymus

冰草属披碱草与小麦、大麦和黑麦同属一类。该属中的牧草适应了不同的气候和生境，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类群。所有的冰草都是由至少两组不同的染色体组成的，大多数物种都有S染色体和S染色体的组合。与Sth组合的物种约有50种。ST基因组来自假鹅观草属的祖先种，H来自野生大麦。关于这一群体的一个争论是，不同的Sth物种是由一对亲本、拟鹅观草属物种和野生大麦之间的古代杂交产生的，然后分化为多个物种(单一起源)，还是不同的Sth物种是由不同的双亲在不同的时间和地点杂交产生的(多个起源)。我们将测试披碱草的ST和H基因组是否具有多重来源。异源多倍体物种可能起源于同源多倍体(StStST)，相同的基因组在多倍体物种内逐渐分化，从而产生了今天的同源四倍体披碱草基因组。我们的rpb2数据不支持STY物种中ST和Y基因组的相同来源。对猪瘟物种uSig其他基因的系统发育分析将检验猪瘟物种是否是异源多倍体起源。我的研究旨在测试Sth物种中的ST和H单倍体是否具有多重起源，并表征细胞遗传学上不同的Sth物种和STY物种之间的差异。最后，我将测试STY基因组物种是异源多倍体起源还是同源多倍体起源，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.