Symbiotic germination and development of fully mycoheterotrophic plants convergently targeting similar Glomeraceae taxa

Plants producing dust seeds often meet their carbon demands by exploiting fungi at the seedling stage. This germination strategy (i.e. mycoheterotrophic germination) has been investigated among orchidaceous and ericaceous plants exploiting Ascomycota or Basidiomycota. Although several other angiosperm lineages have evolved fully mycoheterotrophic relationships with Glomeromycota, the fungal identities involved in mycoheterotrophic germination remain largely unknown. Here, we conducted in situ seed baiting and high-throughput DNA barcoding to identify mycobionts associated with seedlings of Burmannia championii (Burmanniaceae: Dioscoreales) and Sciaphila megastyla (Triuridaceae: Pandanales), which have independently evolved full mycoheterotrophy. Subsequently, we revealed that both seedlings and adults in B. championii and S. megastyla predominantly associate with Glomeraceae. However, mycorrhizal communities are somewhat distinct between seedling and adult stages, particularly in S. megastyla. Notably, the dissimilarity of mycorrhizal communities between S. megastyla adult samples and S. megastyla seedling samples is significantly higher than that between B. championi adult samples and S. megastyla adult samples, based on some indices. This pattern is possibly due to both mycorrhizal shifts during ontogenetic development and convergent recruitment of cheating-susceptible fungi. The extensive fungal overlap in two unrelated mycoheterotrophic plants indicates that both species convergently exploit specific AM fungal phylotypes.