In general, Glomeromycotina was thought to be the earliest fungi forming mycorrhiza-like structure (MLS) in land plant evolution. In contrast, because the earliest divergent lineage of extant land plants, i.e. Haplomitriopsida liverworts, associates only with Mucoromycotina mycobionts, recent studies suggested that those fungi are novel candidates for the earliest mycobionts. Therefore, Mucoromycotina-Haplomitriopsida association currently attracts attention as an ancient mycorrhiza-like association. However, mycobionts were identified in only 7 of 16 Haplomitriopsida species and the mycobionts diversity of this lineage is largely unclarified. To clarify the taxonomic composition of mycobionts in Haplomitriopsida, we observed MLSs in the rhizome of Haplomitrium mnioides (Haplomitriopsida), the Asian representative Haplomitriopsida species, and conducted molecular identification of mycobionts. It was recorded for the first time that Glomeromycotina and Mucoromycotina co-occur in Haplomitriopsida as mycobionts. Significantly, the arbuscule-like branching (ALB) of Glomeromycotina was newly described. As the Mucoromycotina fungi forming MLSs in H. mnioides, Endogonaceae and Densosporaceae were detected, in which size differences of hyphal swelling (HS) were found between the fungal families. This study provides a novel evidence in the MLS of Haplomitriopsida, i.e. the existence of Glomeromycotina association as well as the dominant Mucoromycotina association. In addition, since hyphal characteristics of the HS-type MLS were quite similar to those of fine endophytes (FE) of Endogonales in other bryophytes and vascular plants previously described, this MLS is suggested to be included in FE. These results suggest that Glomeromycotina and Mucoromycotina were acquired concurrently as the mycobionts by the earliest land plants evolved into arbuscular mycorrhizae and FE. Therefore, dual association of Haplomitriopsida, with Endogonales and Glomeromycotina will provide us novel insight on how the earliest land plants adapted to terrestrial habitats with fungi.

中文翻译：

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基底地草，羊角线虫（Haplomitrium mnioides（Haplomitriopsida））中的毛壁菌和球菌真菌双重定植。

一般而言，glomeromycotina被认为是陆地植物进化中最早形成菌根样结构（MLS）的真菌。相比之下，由于现存陆地植物的最早分化谱系，即Haplomitriopsida liverworts仅与毛霉菌霉菌相关，因此最近的研究表明，这些真菌是最早的霉菌菌的候选者。因此，作为古老的菌根样的协会，毛霉菌-单孢菌病协会目前受到关注。但是，仅在16个单倍体线虫科物种中有7种被鉴定为菌丝体，该谱系的菌丝体多样性在很大程度上尚不清楚。为了弄清楚单倍体中菌丝体的分类学组成，我们在亚洲代表性单倍体物种羊角线虫（Haplomitriopsida）的根茎中观察到了MLS，并对霉菌进行分子鉴定。首次记录了在单倍孢子虫中同时出现了球囊菌和毛囊菌。重要的是，新近描述了球囊球菌的丛状分支（ALB）。羊膜毛虫中的毛霉菌真菌形成了MLS，检测到了禾本科和草科，在真菌家族之间发现了菌丝肿胀（HS）的大小差异。这项研究提供了单倍体MLS的新证据，即存在肾小球菌协会和显性毛囊菌协会。此外，由于HS型MLS的菌丝特征与先前描述的其他苔藓植物和维管植物中的内生细小内生菌（FE）的菌丝特征非常相似，建议将此MLS包含在FE中。这些结果表明，随着最早的陆地植物的菌丝体进化成丛枝菌根和FE，Glomeromycotina和Mucoromycotina被同时获得。因此，Haplomitriopsida与Endogonales和Glomeromycotina的双重关联将为我们提供关于最早的陆地植物如何适应真菌的陆地生境的新颖见解。