Origin and Evolution of Allopolyploid Wheatgrass Elymus fibrosus (Schrenk) Tzvelev (Poaceae: Triticeae) Reveals the Effect of Its Origination on Genetic Diversity

Origin and evolution of tetraploid Elymus fibrosus (Schrenk) Tzvelev were characterized using low-copy nuclear gene Rpb2 (the second largest subunit of RNA polymerase II), and chloroplast region trnL–trnF (spacer between the tRNA Leu (UAA) gene and the tRNA-Phe (GAA) gene). Ten accessions of E. fibrosus along with 19 Elymus species with StH genomic constitution and diploid species in the tribe Triticeae were analyzed. Chloroplast trnL–trnF sequence data suggested that Pseudoroegneria (St genome) was the maternal donor of E. fibrosus. Rpb2 data confirmed the presence of StH genomes in E. fibrosus, and suggested that St and H genomes in E. fibrosus each is more likely originated from single gene pool. Single origin of E. fibrosus might be one of the reasons causing genetic diversity in E. fibrosus lower than those in E. caninus and E. trachycaulus, which have similar ecological preferences and breeding systems with E. fibrosus, and each was originated from multiple sources. Convergent evolution of St and H copy Rpb2 sequences in some accessions of E. fibrosus might have occurred during the evolutionary history of this allotetraploid.

本研究依托低拷贝核基因Rpb2（RNA聚合酶II第二大亚基，RNA polymerase II second largest subunit）与叶绿体区间trnL–trnF（tRNA亮氨酸(UAA)基因与tRNA苯丙氨酸(GAA)基因间的间隔序列），对四倍体纤维披碱草（Elymus fibrosus (Schrenk) Tzvelev）的起源与演化特征展开解析。研究共分析了10份纤维披碱草种质材料，连同19个携带StH基因组构成的披碱草属物种，以及小麦族（Triticeae）的二倍体物种。叶绿体trnL–trnF序列数据表明，拟鹅观草属（Pseudoroegneria，St基因组供体）为纤维披碱草的母本供体。Rpb2基因序列数据证实了纤维披碱草中存在St与H基因组，且该物种的St、H基因组更倾向于分别起源于单一基因库。纤维披碱草的单次起源事件，可能是导致其遗传多样性低于犬披碱草（Elymus caninus）与硬秆披碱草（Elymus trachycaulus）的原因之一；后两者与纤维披碱草具有相似的生态偏好与繁育系统，且二者均为多起源物种。在该异源四倍体（allotetraploid）的演化历程中，部分纤维披碱草种质材料的St与H拷贝Rpb2序列或已发生趋同演化。