Small R L, Wendel J F
Department of Botany, Iowa State University, Iowa, Ames, 50011, USA.
Mol Phylogenet Evol. 2000 Jul;16(1):73-84. doi: 10.1006/mpev.1999.0750.
The 13 "D-genome"cotton species are a monophyletic assemblage of morphologically diverse diploids that inhabit arid to semiarid regions in Mexico, with 1 disjunct species each in Peru and the Galapagos Islands and 1 species whose range extends northward into Arizona. While these species lack commercially significant fiber (i. e., cotton), they are important in that they represent one of the parental genomes of the cultivated tetraploid cottons. To assess phylogenetic relationships among these species, we sequenced and analyzed a region of a nuclear-encoded alcohol dehydrogenase gene (AdhA). Phylogenetic analysis resulted in a topology that is generally consistent with current taxonomic alignment of the species, although the phylogeny based on AdhA sequences conflicts with those inferred from cpDNA and ITS data sets, most notably in the position of the anomalous species Gossypium gossypioides. In one lineage, we detected both gene duplication and sequence polymorphisms that transcend species boundaries; sequences in this lineage formed a monophyletic clade, yet no taxon within the clade contained a monophyletic collection of sequences. Potential explanations for this latter phenomenon, including gene duplication, gene flow, and lineage sorting, are discussed.
13个“D基因组”棉种是形态多样的二倍体单系类群，分布于墨西哥的干旱至半干旱地区，在秘鲁和加拉帕戈斯群岛各有1个间断分布的物种，还有1个物种的分布范围向北延伸至亚利桑那州。虽然这些物种缺乏具有商业价值的纤维（即棉花），但它们很重要，因为它们代表了栽培四倍体棉花的亲本基因组之一。为了评估这些物种之间的系统发育关系，我们对一个核编码乙醇脱氢酶基因（AdhA）的区域进行了测序和分析。系统发育分析得出的拓扑结构总体上与该物种当前的分类排列一致，尽管基于AdhA序列的系统发育与从cpDNA和ITS数据集推断的系统发育存在冲突，最明显的是异常物种海岛棉（Gossypium gossypioides）的位置。在一个谱系中，我们检测到了跨越物种界限的基因重复和序列多态性；该谱系中的序列形成了一个单系分支，但该分支内没有一个分类单元包含单系的序列集合。本文讨论了后一种现象的潜在解释，包括基因重复、基因流动和谱系分选。
