Ancient allopolyploid speciation in geinae (Rosaceae): Evidence from nuclear granule-bound starch synthase (GBSSI) gene sequences
Ancient allopolyploid speciation in geinae (Rosaceae): Evidence from nuclear granule-bound starch synthase (GBSSI) gene sequences
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DOI：
10.1080/10635150390197000
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发表时间：
2003-06-01
影响因子：
6.5
通讯作者：
Campbell, CS
中科院分区：
文献类型：
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作者：
Smedmark, JEE;Eriksson, T;Campbell, CS
核低拷贝基因系统发育为蔷薇科7个多倍体种的杂交起源提供了有力证据。在基因树中，异体多倍体物种中同源位点的等位基因与祖先分类群中的同源基因是姐妹关系，而不是彼此之间的姐妹关系。然而，自多倍体中一个重复位点上的等位基因彼此之间的亲缘关系比它们在密切相关的物种中与任何同源拷贝的亲缘关系更密切。我们克隆并测序了2个二倍体、1个四倍体和6个六倍体物种的GBSSI-1基因50端约1.9千碱基。在六倍体物种中，这三个位点中的每一个都形成了一个单独的组，其中两个与其他物种的拷贝关系比它们彼此之间的关系更密切。这一发现表明六倍体谱系是通过两次连续的异源多倍体事件进化而来的。基于GBSSI-1基因树，我们假设来自哥伦比亚和瓦尔德斯坦祖先谱系的二倍体物种与未知的二倍体物种之间存在初始杂交，形成了四倍体Geum heterocarpum谱系。通过与未知的二倍体谱系的一个代表进行回交，得到了一个六倍体谱系，该谱系自其起源以来辐射相当大，包括至少40个具有不同形态的现存物种。惩罚似然分析表明，Geinae可能大约有1700万年的历史，这意味着假设的异源多倍体物种形成事件相对较早。本研究克隆的22个Geinae GBSSI-1拷贝中有6个可能成为假基因，这些拷贝均为多倍体类群中的重复拷贝。我们将GBSSI-1的系统发育与叶绿体数据的系统发育进行了比较，并探讨了其对某些果实性状进化的启示。
A nuclear low-copy gene phylogeny provides strong evidence for the hybrid origin of seven polyploid species in Geinae ( Rosaceae). In a gene tree, alleles at homoeologous loci in an allopolyploid species are expected to be sisters to orthologues in the ancestral taxa rather than to each other. Alleles at a duplicated locus in an autopolyploid, however, are expected to be more closely related to each other than they are to any orthologous copies in closely related species. We cloned and sequenced about 1.9 kilobases from the 50 end of the GBSSI-1 gene from two diploid, one tetraploid, and six hexaploid species. Each of the three loci in the hexaploid species forms a separate group, two of which are more closely related to copies in other species than they are to each other. This finding indicates that the hexaploid lineage evolved through two consecutive allopolyploidization events. Based on the GBSSI-1 gene tree, we hypothesized that there was an initial hybridization between a diploid species from the ancestral lineage of Coluria and Waldsteinia and an unknown diploid species to form the tetraploid Geum heterocarpum lineage. Backcrossing of G. heterocarpum with a representative of the unknown diploid lineage then resulted in a hexaploid lineage that has radiated considerably since its origin, comprising at least 40 extant species with various morphologies. A penalized likelihood analysis indicated that Geinae may be about 17 million years old, implying that the hypothesized allopolyploid speciation events are relatively ancient. Six of the 22 cloned Geinae GBSSI-1 copies in this study, which all are duplicate copies in polyploid taxa, may have become pseudogenes. We compared the GBSSI-1 phylogeny with one from chloroplast data and explored implications for the evolution of some fruit characters.