SMALL SUBUNIT RIBOSOMAL RNA+ OF HEXAMITA-INFLATA AND THE QUEST FOR THE 1ST BRANCH IN THE EUKARYOTIC TREE
SMALL SUBUNIT RIBOSOMAL RNA+ OF HEXAMITA-INFLATA AND THE QUEST FOR THE 1ST BRANCH IN THE EUKARYOTIC TREE
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DOI：
10.1016/0166-6851(93)90005-i
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发表时间：
1993-05-01
影响因子：
1.5
通讯作者：
SOGIN, ML
中科院分区：
文献类型：
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作者：
LEIPE, DD;GUNDERSON, JH;SOGIN, ML
对膨胀六脚蝇小亚基核糖体RNA （16s样rRNA）编码区的系统发育分析表明，单靠寄生不能解释早期分化的真核生物谱系。寄生和自由生活的外交家，以及滴虫和小孢子虫，在真核生物树的基部分化。单孔虫、滴虫和微孢子虫的相对分支顺序受到其rRNA编码区G + C组成不同的外围原核类群的影响。高G + C原核生物将兰氏贾第虫置于真核生物树的底部，但将外交家分裂成一个副核群。当外围群体被限制为具有名义G + C组成的rnas时，双源体形成一个单系群体，在微孢子虫和滴虫之后分化。这种不稳定的分支模式与G. lamblia （75% G + C）和Vairimorpha necatrix （35% G + C）的rrna中不寻常的核苷酸组成有关。相比之下，H. inflata rRNA的51% G + C组成是其他真核生物rRNA的典型组成。它在滴虫之后的分化得到了距离分析中不包括G. lambla的自举复制的有力支持。由于其rRNA编码区含有较低的G + C组成，V. necatrix的系统发育位置是不确定的，并且最深分支真核谱系的身份是不明确的。
A phylogenetic analysis of the small subunit ribosomal RNA (16S-like rRNA) coding region from Hexamita inflata demonstrates that parasitism alone cannot explain early diverging eukaryotic lineages. Parasitic and free-living diplomonads, as well as trichomonads and microsporidia, diverge at the base of the eukaryotic tree. The relative branching order of diplomonads, trichomonads and microsporidia is influenced by outlying prokaryotic taxa with different G + C compositions in their rRNA coding regions. The high G + C prokaryotes position Giardia lamblia at the base of the eukaryotic tree but split diplomonads into a paraphyletic group. When the outlying groups are restricted to rRNAs with nominal G + C compositions, diplomonads form a monophyletic group that diverged after the microsporidia and trichomonads. This unstable branching pattern correlates with unusual nucleotide compositions in the rRNAs of G. lamblia (75% G + C) and Vairimorpha necatrix (35% G + C). In contrast, the 51% G + C composition of the H. inflata rRNA is typical of other eukaryotic rRNAs. Its divergence after trichomonads is strongly supported by bootstrap replicates in distance analyses that do not include G. lamblia. Because of a low G + C composition in its rRNA coding region, the phylogenetic placement of V. necatrix is uncertain and the identity of the deepest branching eukaryotic lineage is ambiguous.