Department of Biology, University of Ottawa, Ottawa, ON, Canada.
Institute of Botany, The Czech Academy of Sciences, Průhonice, Czech Republic; Institute of Experimental Botany, The Czech Academy of Science, Prague, Czech Republic.
Curr Biol. 2021 Apr 12;31(7):1570-1577.e4. doi: 10.1016/j.cub.2021.01.058. Epub 2021 Feb 15.
Arbuscular mycorrhizal fungi (AMF) (subphylum Glomeromycotina) are among the most prominent symbionts and form the Arbuscular Mycorrhizal symbiosis (AMS) with over 70% of known land plants. AMS allows plants to efficiently acquire poorly soluble soil nutrients and AMF to receive photosynthetically fixed carbohydrates. This plant-fungus symbiosis dates back more than 400 million years and is thought to be one of the key innovations that allowed the colonization of lands by plants. Genomic and genetic analyses of diverse plant species started to reveal the molecular mechanisms that allowed the evolution of this symbiosis on the host side, but how and when AMS abilities emerged in AMF remain elusive. Comparative phylogenomics could be used to understand the evolution of AMS. However, the availability of genome data covering basal AMF phylogenetic nodes (Archaeosporales, Paraglomerales) is presently based on fragmentary protein coding datasets.Geosiphon pyriformis (Archaeosporales) is the only fungus known to produce endosymbiosis with nitrogen-fixing cyanobacteria (Nostoc punctiforme) presumably representing the ancestral AMF state. Unlike other AMF, it forms long fungal cells ("bladders") that enclose cyanobacteria. Once in the bladder, the cyanobacteria are photosynthetically active and fix nitrogen, receiving inorganic nutrients and water from the fungus. Arguably, G. pyriformis represents an ideal candidate to investigate the origin of AMS and the emergence of a unique endosymbiosis. Here, we aimed to advance knowledge in these questions by sequencing the genome of G. pyriformis, using a re-discovered isolate.
丛枝菌根真菌（AMF）（Glomeromycotina 亚门）是最主要的共生体之一，与超过 70%的已知陆地植物形成丛枝菌根共生（AMS）。AMS 使植物能够有效地获取难溶性土壤养分，而 AMF 则接收光合作用固定的碳水化合物。这种植物-真菌共生关系可以追溯到 4 亿多年前，被认为是植物能够在陆地上殖民的关键创新之一。对不同植物物种的基因组和遗传分析开始揭示允许这种共生在宿主侧进化的分子机制，但 AMF 获得 AMS 能力的方式和时间仍然难以捉摸。比较系统发生基因组学可用于理解 AMS 的进化。然而，目前覆盖 AMF 系统发育基础节点（Archaeosporales、Paraglomerales）的基因组数据可用性基于零碎的蛋白质编码数据集。Geosiphon pyriformis（Archaeosporales）是已知与固氮蓝藻（Nostoc punctiforme）产生内共生的唯一真菌，可能代表了祖先 AMF 的状态。与其他 AMF 不同，它形成长的真菌细胞（“膀胱”），将蓝藻包围在其中。一旦进入膀胱，蓝藻就具有光合作用活性并固定氮，从真菌中接收无机养分和水。可以说，G. pyriformis 是研究 AMS 起源和独特内共生出现的理想候选者。在这里，我们旨在通过重新发现的分离物测序 G. pyriformis 的基因组来推进这些问题的知识。
