Division of Parasitology, Faculty of Medicine, University of Miyazaki, Miyazaki 889-1692, Japan.
BMC Evol Biol. 2014 Apr 1;14:69. doi: 10.1186/1471-2148-14-69.
Horizontal gene transfer (HGT) has been suggested as the mechanism by which various plant parasitic nematode species have obtained genes important in parasitism. In particular, cellulase genes have been acquired by plant parasitic nematodes that allow them to digest plant cell walls. Unlike the typical glycoside hydrolase (GH) family 5 cellulase genes which are found in several nematode species from the order Tylenchida, members of the GH45 cellulase have only been identified in a cluster including the families Parasitaphelenchidae (with the pinewood nematode Bursaphelenchus xylophilus) and Aphelenchoididae, and their origins remain unknown.
In order to investigate the distribution and evolution of GH45 cellulase genes in nematodes and fungi we performed a wide ranging screen for novel putative GH45 sequences. This revealed that the sequences are widespread mainly in Ascomycetous fungi and have so far been found in a single major nematode lineage. Close relationships between the sequences from nematodes and fungi were found through our phylogenetic analyses. An intron position is shared by sequences from Bursaphelenchus nematodes and several Ascomycetous fungal species.
The close phylogenetic relationships and conserved gene structure between the sequences from nematodes and fungi strongly supports the hypothesis that nematode GH45 cellulase genes were acquired via HGT from fungi. The rapid duplication and turnover of these genes within Bursaphelenchus genomes demonstrate that useful sequences acquired via HGT can become established in the genomes of recipient organisms and may open novel niches for these organisms to exploit.
水平基因转移（HGT）被认为是各种植物寄生线虫获得寄生重要基因的机制。特别是，纤维素酶基因已被植物寄生线虫获得，使它们能够消化植物细胞壁。与典型的糖苷水解酶（GH）家族 5 纤维素酶基因不同，这些基因存在于几个线虫目中的几个线虫物种中，GH45 纤维素酶的成员仅在包括拟寄生科（包括松材线虫 Bursaphelenchus xylophilus）和滑刃科的聚类中被鉴定出来，它们的起源仍然未知。
为了研究 GH45 纤维素酶基因在线虫和真菌中的分布和进化，我们广泛筛选了新的推定 GH45 序列。这表明这些序列主要分布在子囊菌中，迄今为止仅在一个主要的线虫谱系中发现。通过我们的系统发育分析发现，线虫和真菌的序列之间存在密切的关系。来自线虫和真菌的序列共享一个内含子位置。
线虫和真菌序列之间密切的系统发育关系和保守的基因结构强烈支持了线虫 GH45 纤维素酶基因通过 HGT 从真菌中获得的假设。Bursaphelenchus 基因组中这些基因的快速重复和更替表明，通过 HGT 获得的有用序列可以在受体生物的基因组中建立，并为这些生物开辟新的利用途径。
