Humphreys-Pereira Danny A, Elling Axel A
Department of Plant Pathology, Washington State University, Pullman, WA 99164, USA.
Department of Plant Pathology, Washington State University, Pullman, WA 99164, USA.
Mol Biochem Parasitol. 2014 Mar-Apr;194(1-2):20-32. doi: 10.1016/j.molbiopara.2014.04.003. Epub 2014 Apr 19.
Root-knot nematodes (Meloidogyne spp.) are among the most important plant pathogens. In this study, the mitochondrial (mt) genomes of the root-knot nematodes, M. chitwoodi and M. incognita were sequenced. PCR analyses suggest that both mt genomes are circular, with an estimated size of 19.7 and 18.6-19.1kb, respectively. The mt genomes each contain a large non-coding region with tandem repeats and the control region. The mt gene arrangement of M. chitwoodi and M. incognita is unlike that of other nematodes. Sequence alignments of the two Meloidogyne mt genomes showed three translocations; two in transfer RNAs and one in cox2. Compared with other nematode mt genomes, the gene arrangement of M. chitwoodi and M. incognita was most similar to Pratylenchus vulnus. Phylogenetic analyses (Maximum Likelihood and Bayesian inference) were conducted using 78 complete mt genomes of diverse nematode species. Analyses based on nucleotides and amino acids of the 12 protein-coding mt genes showed strong support for the monophyly of class Chromadorea, but only amino acid-based analyses supported the monophyly of class Enoplea. The suborder Spirurina was not monophyletic in any of the phylogenetic analyses, contradicting the Clade III model, which groups Ascaridomorpha, Spiruromorpha and Oxyuridomorpha based on the small subunit ribosomal RNA gene. Importantly, comparisons of mt gene arrangement and tree-based methods placed Meloidogyne as sister taxa of Pratylenchus, a migratory plant endoparasitic nematode, and not with the sedentary endoparasitic Heterodera. Thus, comparative analyses of mt genomes suggest that sedentary endoparasitism in Meloidogyne and Heterodera is based on convergent evolution.
根结线虫（Meloidogyne属）是最重要的植物病原体之一。在本研究中，对根结线虫南方根结线虫（M. incognita）和奇氏根结线虫（M. chitwoodi）的线粒体（mt）基因组进行了测序。PCR分析表明，两个线粒体基因组均为环状，估计大小分别为19.7kb和18.6 - 19.1kb。每个线粒体基因组都包含一个具有串联重复序列的大非编码区和控制区。奇氏根结线虫和南方根结线虫的线粒体基因排列与其他线虫不同。两种根结线虫线粒体基因组的序列比对显示有三个易位；两个发生在转运RNA中，一个发生在细胞色素氧化酶亚基Ⅱ（cox2）中。与其他线虫线粒体基因组相比，奇氏根结线虫和南方根结线虫的基因排列与穿刺短体线虫（Pratylenchus vulnus）最为相似。使用78种不同线虫物种的完整线粒体基因组进行了系统发育分析（最大似然法和贝叶斯推断）。基于12个蛋白质编码线粒体基因的核苷酸和氨基酸进行的分析有力地支持了色矛纲（Chromadorea）的单系性，但只有基于氨基酸的分析支持了刺嘴纲（Enoplea）的单系性。在任何系统发育分析中，旋尾亚目（Spirurina）都不是单系的，这与基于小亚基核糖体RNA基因将蛔形目（Ascaridomorpha）、旋尾目（Spiruromorpha）和尖尾目（Oxyuridomorpha）归为一类的进化枝Ⅲ模型相矛盾。重要的是，线粒体基因排列的比较和基于树的方法将根结线虫置于迁移性植物内寄生线虫穿刺短体线虫的姐妹类群位置，而不是与定居性内寄生线虫异皮线虫（Heterodera）在一起。因此，线粒体基因组的比较分析表明，根结线虫和异皮线虫的定居性内寄生是基于趋同进化。
