Department of Biology, University of Ottawa, Ottawa, ON K1N 6N5, Canada.
Department of Biological Sciences, University of Toronto Scarborough, Toronto, Canada.
Microb Genom. 2022 Apr;8(4). doi: 10.1099/mgen.0.000810.
The arbuscular mycorrhizal fungi (AMFs) are obligate root symbionts in the subphylum Glomeromycotina that can benefit land plants by increasing their soil nutrient uptake in exchange for photosynthetically fixed carbon sources. To date, annotated genome data from representatives of the AMF orders Glomerales, Diversisporales and Archaeosporales have shown that these organisms have large and highly repeated genomes, and no genes to produce sugars and fatty acids. This led to the hypothesis that the most recent common ancestor (MRCA) of Glomeromycotina was fully dependent on plants for nutrition. Here, we aimed to further test this hypothesis by obtaining annotated genome data from a member of the early diverging order Paraglomerales (). Genome analyses showed this species carries a 39.6 Mb genome and considerably fewer genes and repeats compared to most AMF relatives with annotated genomes. Consistent with phylogenies based on ribosomal genes, our phylogenetic analyses suggest as the earliest diverged branch within Glomeromycotina. Overall, our analyses support the view that the MRCA of Glomeromycotina carried hallmarks of obligate plant biotrophy. The small genome size and content of could either reflect adaptive reductive processes affecting some early AMF lineages, or indicate that the high gene and repeat family diversity thought to drive AMF adaptability to host and environmental change was not an ancestral feature of these prominent plant symbionts.
丛枝菌根真菌（AMF）是在球囊霉亚门中与植物根系形成共生体的专性共生菌，它们可以通过增加植物对土壤养分的吸收来促进陆地植物的生长，作为交换，植物则为真菌提供光合作用固定的碳源。迄今为止，AMF 目（Glomerales、Diversisporales 和 Archaeosporales）代表的注释基因组数据表明，这些生物具有庞大且高度重复的基因组，并且没有产生糖和脂肪酸的基因。这导致了一个假说，即球囊霉亚门的最接近共同祖先（MRCA）完全依赖植物获取营养。在这里，我们旨在通过获得一个早期分化的类群——丛块菌目（Paraglomerales）成员的注释基因组数据来进一步检验这一假说。基因组分析表明，与具有注释基因组的大多数 AMF 相关生物相比，该物种的基因组大小为 39.6 Mb，并且基因和重复序列数量较少。与基于核糖体基因的系统发育一致，我们的系统发育分析表明， 是球囊霉亚门中最早分化的分支。总的来说，我们的分析支持了这样一种观点，即球囊霉亚门的 MRCA 具有专性植物寄生生物的特征。Glomeromycotina 的小基因组大小和 可能反映了影响一些早期 AMF 谱系的适应性还原过程，或者表明，被认为驱动 AMF 适应宿主和环境变化的高基因和重复家族多样性并不是这些主要植物共生体的一个祖先特征。
