Ainouche M L, Bayer R J
Department of Biological Sciences, University of Alberta, Edmonton, Canada.
Genome. 1997 Oct;40(5):730-43. doi: 10.1139/g97-796.
The internal transcribed spacer (ITS) region of nuclear ribosomal DNA from 22 diploid and tetraploid annual Bromus species of section Bromus (Poaceae) and three species belonging to other Bromus sections, Bromus catharticus (section Ceratochloa), Bromus anomalus (section Pnigma), and Bromus sterilis (section Genea), were investigated by PCR amplification and direct sequencing. The length of the ITS-1 region varied from 215 to 218 bp, and that of the ITS-2 region from 215 to 216 bp, in the species analyzed. ITS-1 was more variable and provided more informative sites (49) than ITS-2 (32). No variation was encountered within species. In pairwise comparison among species of section Bromus, sequence divergence ranged from 0.0 to 8.0% for the combined ITS-1 and ITS-2 regions. Parsimony analysis using Avena longiglumis and Hordeum vulgare as outgroups resulted in well-resolved phylogenetic trees and showed that section Bromus is monophyletic according to the species analyzed outside of the section. The analysis clarified the phylogenetic relationships among monogenomic (diploid) species. Introduction of the allotetraploid species did not change the general topology of the trees obtained using only the diploid species. Although some tetraploid-diploid species relationships will have to be clarified with faster evolving markers, the ITS sequences are shown to be useful for assessing evolutionary relationships among closely related Bromus species, as well as for clarifying taxonomic problems in previously controversial cases (e.g., Bromus alopecuros and Bromus caroli-henrici). New hypotheses are proposed concerning the origin of several allotetraploid species. For example, it is shown that the tetraploid Bromus hordeaceus diverged earlier than all other species of section Bromus, excluding the diploid B. caroli-henrici, which is found to be basal in this group. The tetraploid Bromus arenarius, which was considered a hybrid between sections Bromus and Genea, and the tetraploid Bromus adoensis are sister taxa within section Bromus; they belong in a weakly differentiated clade with the diploids Bromus brachystachys, Bromus japonicus, Bromus squarrosus, Bromus arvensis, and Bromus intermedius.
对禾本科雀麦属22个二倍体和四倍体一年生雀麦物种以及其他雀麦属三个物种（净化雀麦（角雀麦组）、异常雀麦（皮雀麦组）和不育雀麦（吉纳雀麦组））的核糖体DNA内转录间隔区（ITS）进行了PCR扩增和直接测序研究。在所分析的物种中，ITS-1区域长度在215至218 bp之间，ITS-2区域长度在215至216 bp之间。ITS-1比ITS-2更具变异性，提供了更多信息位点（49个对32个）。在物种内未发现变异。在雀麦组物种的两两比较中，ITS-1和ITS-2区域合并后的序列分歧范围为0.0%至8.0%。以长颖燕麦和大麦为外类群进行简约分析，得到了分辨率良好的系统发育树，结果表明，根据该组以外分析的物种，雀麦组是单系的。该分析阐明了单基因组（二倍体）物种之间的系统发育关系。引入异源四倍体物种并没有改变仅使用二倍体物种得到的树的总体拓扑结构。尽管一些四倍体-二倍体物种关系还需要用进化更快的标记来阐明，但ITS序列被证明可用于评估近缘雀麦物种之间的进化关系，以及澄清先前有争议案例中的分类学问题（如无芒雀麦和卡罗利-亨利雀麦）。提出了关于几个异源四倍体物种起源的新假设。例如，研究表明四倍体长芒雀麦比雀麦组的所有其他物种分化更早，但不包括二倍体卡罗利-亨利雀麦，后者在该组中处于基部位置。四倍体沙生雀麦被认为是雀麦组和吉纳雀麦组之间的杂交种，四倍体阿多雀麦是雀麦组内的姐妹类群；它们与二倍体短穗雀麦、日本雀麦、糙雀麦、田雀麦和中间雀麦属于一个分化较弱的分支。
