Molecular analysis of mite mitochondrial genome structure

线粒体基因组的基因含量在后生动物中通常是保守的。细恙螨属恙螨的基因重排为37个，且有较大的非编码区（LNR）。这些基因在其他革螨（Ascoschoengastia sp.和Walchia hayashii）中也大量发生了重组、甚至不同方向的重新定位和基因重复。我们发现，除了后生动物（Metazoa）的37个基因和一个典型的LNR外，pallidum的mt基因组还有一个额外的大亚单位rRNA （rrnL）基因、一个小亚单位rRNA （PrrnS）伪基因和三个额外的LNR。此外，苍白草的mt基因排列与节肢动物的假设祖先有很大的不同。为了了解该基因在细恙体虫中出现的程度，我们对另外4种细恙体虫（akamushi、l.d elense、Ascoschoengastia sp.、Walchia hayashi）的全部基因组和部分序列进行了测序，并对L.fletcheri、l.s scutellare、l.m intermedium、l.l chaingraiensis、l.l imphalum、L.fujii、Leptotrombidium sp.)的基因组进行了测序。除trnQ（用于trna -谷氨酰胺）外，其他细螺旋体种与L. pallidum共享或部分共享所有基因。然而，与l.p aldum不同的是，这些其他物种没有额外的rrnL或PrrnS，只有一个额外的LNR。通过对细鳞龙属和节肢动物祖先的比较，我们提出：(1)细鳞龙属的mt基因组类型是由其他3种细鳞龙属的mt基因组类型进化而来；(2)细鳞龙属mt基因含量和基因排列的进化涉及3种分子机制。

The gene content of a mitochondrial (mt) genome is usually conserved in Metazoa. In contrast, the re-arrangement of these genes, 37 genes and large noncoding region (LNR), was observed in chigger mites of the genus Leptotombidium. Recombination of theses genes, relocation in even different direction, and gene duplication were also occurred substantially in the other acariformes mite (Ascoschoengastia sp. and Walchia hayashii). We found that the mt genome of Leptotrombidium pallidum has an extra gene for large-subunit rRNA (rrnL), a pseudo-gene for small-subunit rRNA (PrrnS), and three extra LNRs, additional to the 37 genes and an LNR typical of Metazoa. Further, the arrangement of mt genes of L. pallidum differs drastically from that of the hypothetical ancestor of the arthropods. To find to what extent the novel gene content and gene arrangement occurred in Leptotrombidium, we sequenced the entire mt genomes of four other species, L.akamushi, L.deliense, Ascoschoengastia sp., and Walchia hayashii, and partially L.fletcheri, L.scutellare, L.intermedium, L.chaingraiensis, L.imphalum, L.fujii, and Leptotrombidium sp. The mit genomes of Ascoschoengastia sp. and W.hayashii were entirely distinct structures from that of Leptotrombidium. The other Leptotrombidium species share the or partial arrangement of all genes with L. pallidum, except trnQ (for tRNA-glutamine). Unlike L.pallidum, however, these other species do not have extra rrnL or PrrnS and have only one extra LNR. By comparison between Leptotrombidium species and the ancestor of the arthropods, we propose that (1) the type of mt genome present in L.pallidum evolved from the type present in the other three Leptotrombidium species, and (2) three molecular mechanisms were involved in the evolution of mt gene content and gene arrangement in Leptotrombidium species.