Seed plant phylogeny inferred from all three plant genomes: Monophyly of extant gymnosperms and origin of Gnetales from conifers
Seed plant phylogeny inferred from all three plant genomes: Monophyly of extant gymnosperms and origin of Gnetales from conifers
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DOI：
10.1073/pnas.97.8.4086
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发表时间：
2000-04-11
影响因子：
11.1
通讯作者：
Palmer, JD
中科院分区：
文献类型：
--
作者：
Chaw, SM;Parkinson, CL;Palmer, JD
目前，五组现存种子植物之间的系统发育关系尚不清楚。例如，形态学研究一致认为买麻藤目是被子植物现存的姐妹群（所谓的“花植物”假说），而一些分子研究恢复裸子植物的单系性，很少有人同意买麻藤目基于形态学的位置。为了更好地解决这些和其他悬而未决的问题，我们已经产生了一个新的线粒体小亚基rRNA序列的分子数据集，并分析了这些数据与核小亚基rRNA基因和叶绿体rbcL基因的可比数据集。所有的细胞核分析都强烈地将买麻藤目与单系针叶树联系在一起，而所有的线粒体分析和那些考虑到第三密码子位置转换饱和度的叶绿体分析实际上将买麻藤目置于针叶树内，作为松科的姐妹群，所有三个基因的综合分析强烈地支持后一种关系，据我们所知，这在以前从未被提出过，综合分析也强烈支持现存裸子植物的单系性，苏铁类被确定为裸子植物的最基部组，银杏作为下一个基部，和所有的针叶树，除了松科作为姐妹的买麻藤+松科分支。根据这些发现，买麻藤目可以被看作是极端分歧的针叶树，被子植物和买麻藤目之间的许多形态相似性（例如，双受精和花状生殖结构）独立出现。
Phylogenetic relationships among the five groups of extant seed plants are presently quite unclear. For example, morphological studies consistently identify the Gnetales as the extant sister group to angiosperms (the so-called "anthophyte" hypothesis), whereas a number of molecular studies recover gymnosperm monophyly, and few agree with the morphology-based placement of Gnetales. To better resolve these and other unsettled issues, we have generated a new molecular data set of mitochondrial small subunit rRNA sequences, and have analyzed these data together with comparable data sets for the nuclear small subunit rRNA gene and the chloroplast rbcL gene. All nuclear analyses strongly ally Gnetales with a monophyletic conifers, whereas all mitochondrial analyses and those chloroplast analyses that take into account saturation of third-codon position transitions actually place Gnetales within conifers, as the sister group to the Pinaceae, Combined analyses of all three genes strongly support this latter relationship, which to our knowledge has never been suggested before, The combined analyses also strongly support monophyly of extant gymnosperms, with cycads identified as the basal-most group of gymnosperms, Ginkgo as the next basal, and all conifers except for Pinaceae as sister to the Gnetales + Pinaceae clade. According to these findings, the Gnetales may be viewed as extremely divergent conifers, and the many morphological similarities between angiosperms and Gnetales (e.g., double fertilization and flower-like reproductive structures) arose independently.