Comparative genomic analysis of a metagenome-assembled genome reveals distinctive symbiotic traits in a Mucoromycotina fine root endophyte arbuscular mycorrhizal fungus.

backgroundRecent evidence shows that arbuscular mycorrhizal (AM) symbiosis, as defined by the presence of arbuscules, is established by two distinct fungal groups, with the distinctive 'fine root endophyte' morphotype formed by fungi from the subphylum Mucoromycotina rather than the sub-phylum Glomeromycotina. While FRE forming fungi are globally distributed, there is currently no understanding of the genomic basis for their symbiosis or how this symbiosis compares to that of other mycorrhizal symbionts.

resultsWe used culture-independent metagenome sequencing to assemble and characterise the metagenome-assembled genome (MAG) of a putative arbuscule forming fine root endophyte, which we show belonged to the family Planticonsortiaceae within the order Densosporales. The MAG shares key traits with Glomeromycotina fungi, which indicate obligate biotrophy, including the absence of fatty acid and thiamine biosynthesis pathways, limited enzymatic abilities to degrade plant cell walls, and a high abundance of calcium transporters. In contrast to Glomeromycotina fungi, it exhibits a higher capacity for degradation of microbial cell walls, a complete cellulose degradation pathway, low abundances of copper, nitrate and ammonium transporters, and a complete pathway for vitamin B6 biosynthesis.

conclusionThese differences, particularly those typically associated with saprotrophic functions, highlight the potential for contrasting interactions between Mucoromycotina and Glomeromycotina fungi with their host plant and the environment. In turn, this could support niche differentiation in resource acquisition and complementary ecological functions.