Mucoromycota: going to the roots of plant-interacting fungi

Many fungi (from micro-to macromycetes) interact with plants as a relevant component of plant microbiota. The aim of the review is to focus on the early diverging fungi (Mucoromycota) whose members establish a wide range of beneficial or pathogenic interactions with their green hosts, depending on their phylogenetic position. While Mortierellomycotina are mostly identified as rhizospheric microbes, Glomeromycotina are acknowledged as the most widespread arbuscular mycorrhizal fungi, leading to the establishment of an ancient and ecologically relevant symbiosis with plants. A combination of data from fossils and from novel observations demonstrates how the third subphylum, Mucoromycotina, is a source of so far largely unidentified plant-interacting fungi. In addition to pathogens, other members establish symbiosis with non-vascular plants, Gymnosperms and Angiosperms producing both ecto- and endomycorrhizas. A survey of the so far sequenced genomes illustrates how these fungi share some genetic traits, mirroring their common origin, while other features are specific for each group. In addition to some shared phenotypic traits (aseptate hyphae, multinuclear conditions) endobacteria belonging to the group of Burkholderia-related and to the Mycoplasma-related bacteria are present in many members of the three subphyla, suggesting that the common ancestor was already hosting endobacteria. The review also underlines some idiosyncrasies mostly due to the lack of fossil reports which may confirm phylogenomics as well as the still limited functional data. (C) 2019 British Mycological Society. Published by Elsevier Ltd. All rights reserved.