Advances in understanding of mycorrhizal-like associations in bryophytes

Abstract

Mutually beneficial associations between plants and soil fungi, mycorrhizas, are one of the most important terrestrial symbioses. These partnerships are thought to have propelled plant terrestrialisation some 500 million years ago and today they play major roles in ecosystem functioning. It has long been known that bryophytes harbour, in their living tissues, fungal symbionts, recently identified as belonging to the three mycorrhizal fungal lineages Glomeromycotina, Ascomycota and Basidiomycota. Latest advances in understanding of fungal associations in bryophytes have been largely driven by the discovery, nearly a decade ago, that early divergent liverwort clades, including the most basal Haplomitriopsida, and some hornworts, engage with a wider repertoire of fungal symbionts than previously thought, including endogonaceous members of the ancient sub-phylum Mucoromycotina. Subsequent global molecular and cytological studies have revealed that Mucoromycotina symbionts, alongside Glomeromycotina, are widespread in both complex and simple thalloid liverworts and throughout hornworts, with physiological studies confirming that, in liverworts at least, these associations are mycorrhizal-like, and highlighting important functional differences between Mucoromycotina and Glomeromycotina symbioses. Whether a more prominent role of Mucoromycotina symbionts in plant nitrogen nutrition, as identified in liverworts, extends to other plant lineages, including the flowering plants, is a major topic for future research.
 The latest finding that ascomycete symbionts of leafy liverworts are not restricted to one fungus, Rhizoscyphus ericae, but include species in the genus Meliniomyces, as shown here in Mylia anomala, together with the recent demonstration that R. ericae forms nutritional mutualisms with the rhizoids of Cephalozia bicuspidata, fill other major gaps in our growing knowledge of fungal associations across land plants.