Mason-Gamer Roberta J
University of Illinois at Chicago, Department of Biological Sciences, MC 066, 845 W. Taylor Street, Chicago, Illinois 60607, USA.
Syst Biol. 2004 Feb;53(1):25-37. doi: 10.1080/10635150490424402.
Recent molecular phylogenetic studies of polyploid plants have successfully clarified complex patterns of reticulate evolution. In this study of Elymus repens, an allohexaploid member of the wheat tribe Triticeae, chloroplast and nuclear DNA data reveal an extreme reticulate pattern, revealing at least five distinct gene lineages coexisting within the species, acquired through a possible combination of allohexaploidy and introgression from both within and beyond the Triticeae. Earlier cytogenetic studies of E. repens suggested that Hordeum (genome H) and Pseudoroegneria (St) were genome donors to E. repens. Chloroplast DNA data presented here (from the rpoA gene and from the region between trnT and trnF) identify three potential maternal genome donors (Pseudoroegneria, Thinopyrum, and Dasypyrum), and information from previous molecular work suggests that, of these, Pseudoroegneria is the most likely maternal donor. Nuclear starch synthase gene data indicate that both Hordeum and Pseudoroegneria have contributed to the nuclear genome of E. repens, in agreement with cytogenetic data. However, these data also show unexpected contributions from Taeniatherum, and from two additional donors of unknown identity. One of the sequences of unknown origin falls within the Triticeae, but is not closely associated with any of the sampled diploid genera. The second falls outside of the clade containing Triticeae and its outgroup Bromus, suggesting the acquisition of genetic material from a surprisingly divergent source. Bias toward the amplification of certain starch synthase variants has complicated attempts to thoroughly sample from within individuals, but the data clearly indicate a complex pattern of reticulate evolution, consistent not only with allohexaploidy, but also with introgression from unexpectedly divergent sources.
近期对多倍体植物的分子系统发育研究成功厘清了复杂的网状进化模式。在这项对小麦族披碱草属异源六倍体成员偃麦草的研究中，叶绿体和核DNA数据揭示了一种极端的网状模式，显示该物种内至少有五个不同的基因谱系共存，这些谱系可能是通过异源六倍体以及来自小麦族内外的基因渗入组合而获得的。早期对偃麦草的细胞遗传学研究表明，大麦（基因组H）和拟鹅观草（St）是偃麦草的基因组供体。此处呈现的叶绿体DNA数据（来自rpoA基因以及trnT和trnF之间的区域）确定了三个潜在的母本基因组供体（拟鹅观草、滨麦属和猬草属），先前分子研究的信息表明，其中拟鹅观草最有可能是母本供体。核淀粉合酶基因数据表明，大麦和拟鹅观草都对偃麦草的核基因组有贡献，这与细胞遗传学数据一致。然而，这些数据还显示出蒺藜草属以及另外两个身份不明的供体的意外贡献。一个来源不明的序列属于小麦族，但与任何采样的二倍体属都没有密切关联。另一个序列落在包含小麦族及其外类群雀麦属的分支之外，这表明遗传物质是从一个惊人的远源获得的。偏向于某些淀粉合酶变体的扩增使从个体内部进行全面采样的尝试变得复杂，但数据清楚地表明了一种复杂的网状进化模式，这不仅与异源六倍体一致，也与来自意外远源的基因渗入一致。
