Ectomycorrhizal symbioses: Diversity of mycobionts and molecular mechanisms that entail the development of ectomycorrhizae

Approximately 2% of vascular plants are involved in ectomycorrhizal symbioses with about 280 genera of higher fungi from 17–18 fungal orders. The development of ectomycorrhizal symbiosis, host specificity, and host-switch events appear to be key drivers for the speciation of ectomycorrhizal fungi. Comparative genomics indicates that ectomycorrhizal fungi have lost a set of genes that control the decay of organic matter contained in plant cell walls. During the formation of ectomycorrhizae, mycobionts and host plants require diversified signaling molecules to induce their bilateral communication; at the same time, mycobionts can release some mycorrhizal-induced small secreted proteins, which can help them escape plant defenses and thereby enable them to colonize plant roots. We present a review on the diversity and geographical distribution pattern of ectomycorrhizal fungi and on molecular mechanisms contributing to the development of ectomycorrhizae. Based on this, we also suggeste several future prospects.