Corradi Nicolas, Kuhn Gerrit, Sanders Ian R
Department of Ecology and Evolution, Biology building, University of Lausanne, 1015 Lausanne, Switzerland.
Fungal Genet Biol. 2004 Feb;41(2):262-73. doi: 10.1016/j.fgb.2003.11.001.
Arbuscular mycorrhizal fungi (AMF) are an ecologically important group of fungi. Previous studies showed the presence of divergent copies of beta-tubulin and V-type vacuolar H+-ATPase genes in AMF genomes and suggested horizontal gene transfer from host plants or mycoparasites to AMF. We sequenced these genes from DNA isolated from an in vitro cultured isolate of Glomus intraradices that was free of any obvious contaminants. We found two highly variable beta-tubulin sequences and variable H+-ATPase sequences. Despite this high variation, comparison of the sequences with those in gene banks supported a glomeromycotan origin of G. intraradices beta-tubulin and H+-ATPase sequences. Thus, our results are in sharp contrast with the previously reported polyphyletic origin of those genes. We present evidence that some highly divergent sequences of beta-tubulin and H+-ATPase deposited in the databases are likely to be contaminants. We therefore reject the prediction of horizontal transfer to AMF genomes. High differences in GC content between glomeromycotan sequences and sequences grouping in other lineages are shown and we suggest they can be used as an indicator to detect such contaminants. H+-ATPase phylogeny gave unexpected results and failed to resolve fungi as a natural group. beta-Tubulin phylogeny supported Glomeromeromycota as sister group of the Chytridiomycota. Contrasts between our results and trees previously generated using rDNA sequences are discussed.
丛枝菌根真菌（AMF）是一类具有重要生态意义的真菌。先前的研究表明，AMF基因组中存在β-微管蛋白和V型液泡H⁺-ATP酶基因的不同拷贝，并推测这些基因是从宿主植物或真菌寄生物水平转移至AMF的。我们从一株体外培养的、无明显污染物的根内球囊霉分离物中提取DNA，对这些基因进行了测序。我们发现了两个高度可变的β-微管蛋白序列和可变的H⁺-ATP酶序列。尽管变异程度很高，但将这些序列与基因库中的序列进行比较后发现，根内球囊霉的β-微管蛋白和H⁺-ATP酶序列起源于球囊菌门。因此，我们的结果与先前报道的这些基因的多系起源形成了鲜明对比。我们提供的证据表明，数据库中一些高度分化的β-微管蛋白和H⁺-ATP酶序列可能是污染物。因此，我们拒绝接受向AMF基因组水平转移的预测。研究显示，球囊菌门序列与其他谱系中的序列在GC含量上存在很大差异，我们认为它们可作为检测此类污染物的指标。H⁺-ATP酶系统发育给出了意外结果，未能将真菌解析为一个自然类群。β-微管蛋白系统发育支持球囊菌门作为壶菌门的姐妹类群。我们讨论了我们的结果与先前使用rDNA序列生成的树状图之间的差异。
