Nishimoto Yuriko, Arisue Nobuko, Kawai Satoru, Escalante Ananias A, Horii Toshihiro, Tanabe Kazuyuki, Hashimoto Tetsuo
The Institute of Statistical Mathematics, Minami-Azabu, Minato-ku, Tokyo 106-8569, Japan.
Mol Phylogenet Evol. 2008 Apr;47(1):45-53. doi: 10.1016/j.ympev.2008.01.031. Epub 2008 Feb 6.
Unlike other eukaryotes, malaria parasites in the genus Plasmodium have structurally and functionally different paralogous copies of the cytosolic (cyto-) SSU rRNA (18S rRNA) gene that are expressed at different developmental stages. In P. falciparum, P. vivax, and P. berghei, A-type cyto-SSU rRNA is expressed in asexual stage, while S-type in sporozoite stage. A third type (O-type) has been described in P. vivax. It is expressed only in oocyst stage in the mosquito. Recently, it has been shown that the maintenance of heterogeneous cyto-SSU rRNAs in Plasmodium can be modeled as a birth-and-death process under strong purifying selection [Rooney, A.P., 2004. Mechanisms underlying the evolution and maintenance of functionally heterogeneous 18S rRNA genes in Apicomplexans. Mol. Biol. Evol. 21, 1704-1711]. In this study, we performed detailed phylogenetic analyses of Plasmodium cyto-SSU rRNAs with special emphasis on the evolution of multi-copy genes in simian Plasmodium species. We sequenced paralogous copies of the cyto-SSU rRNA genes from an African simian Plasmodium species, P. gonderi, and Asian simian Plasmodium species, P. fragile, P. coatneyi, P. inui, P. hylobati, P. fieldi, P. simiovale, and P. cynomolgi. Interestingly, all Asian simian Plasmodium species have a single S-type-like gene and several A-type-like genes. Alignment analysis demonstrated for the first time that an approximately 50-residue insertion in the V7 variable region near the stem 43 is shared exclusively by the S-type-like sequences of the Asian simian Plasmodium species and the S- and O-type sequences of P. vivax. We comprehensively analyzed all cyto-SSU rRNA sequences of the genus Plasmodium currently available in the database. Phylogenetic analyses of all publicly available cyto-SSU rRNA sequences for the genus Plasmodium clearly demonstrated that gene duplication events giving rise to A- and S-type-like sequences took place independently at least three times in the Plasmodium evolution, supporting the hypothesis that these genes evolve according to a birth-and-death model.
与其他真核生物不同，疟原虫属的疟原虫在结构和功能上具有不同的胞质（细胞）小亚基核糖体RNA（18S rRNA）基因旁系同源拷贝，这些拷贝在不同发育阶段表达。在恶性疟原虫、间日疟原虫和伯氏疟原虫中，A型胞质小亚基核糖体RNA在无性阶段表达，而S型在子孢子阶段表达。间日疟原虫中已描述了第三种类型（O型）。它仅在蚊子的卵囊阶段表达。最近，研究表明疟原虫中异质胞质小亚基核糖体RNA的维持可以在强纯化选择下模拟为生死过程[鲁尼，A.P.，2004年。顶复门中功能异质18S rRNA基因进化和维持的潜在机制。分子生物学与进化。21，1704 - 1711]。在本研究中，我们对疟原虫胞质小亚基核糖体RNA进行了详细的系统发育分析，特别强调了猿猴疟原虫物种中多拷贝基因的进化。我们对一种非洲猿猴疟原虫物种冈氏疟原虫以及亚洲猿猴疟原虫物种脆弱疟原虫、科氏疟原虫、井上疟原虫、长臂猿疟原虫、菲氏疟原虫、类人疟原虫和食蟹猴疟原虫的胞质小亚基核糖体RNA基因旁系同源拷贝进行了测序。有趣的是，所有亚洲猿猴疟原虫物种都有一个单一的S型样基因和几个A型样基因。比对分析首次表明，在茎43附近的V7可变区域中约50个残基的插入仅为亚洲猿猴疟原虫物种的S型样序列以及间日疟原虫的S型和O型序列所共有。我们全面分析了数据库中目前可获得的疟原虫属所有胞质小亚基核糖体RNA序列。对疟原虫属所有公开可用的胞质小亚基核糖体RNA序列的系统发育分析清楚地表明，产生A型和S型样序列的基因重复事件在疟原虫进化过程中至少独立发生了三次，支持了这些基因按照生死模型进化的假说。
