Physisporinus is an important mycorrhizal partner for mycoheterotrophic plants: Identification of mycorrhizal fungi of three Yoania species

Abstract Improved understanding of mycorrhizal diversity in mycoheterotrophic (MH) plants is a key element of studies that investigate their evolution. MH plants are completely dependent on their mycorrhizal fungi for carbon. Mycorrhizal fungi of the MH genus Yoania (Orchidaceae), which is distributed in East Asia, have yet to be identified. We identified the mycobionts of three Japanese Yoania species, Y. amagiensis, Y. flava, and Y. japonica, by sequencing the internal transcribed spacer regions of nuclear ribosomal DNA. The sequences obtained were assigned to five operational taxonomic units (OTUs), among which four belonged to the genus Physisporinus (Meripilaceae, Polyporales) and one to Thelephoraceae. Yoania flava and Y. japonica were specifically associated with a single OTU of Physisporinus, while Y. amagiensis was associated with four Physisporinus OTUs. A phylogenetic analysis showed that fungal sequences from species of two other MH orchid genera, Cyrtosia and Galeola, also belonged to Physisporinus and were closely related to the Yoania mycobionts. This is the first study to report that (i) wood-rotting Physisporinus fungi form mycorrhizae with plant species, and (ii) have an important role in orchid mycoheterotrophy.