Laccaria bicolor MiSSP8 is a small-secreted protein decisive for the establishment of the ectomycorrhizal symbiosis

Mycorrhizal symbiosis involves extensive signaling between plants and their fungal partners. Mycorrhiza-induced small secreted proteins (MiSSPs) have been hypothesized to be involved in diverse processes to suppress plant defense and promote fungal life-cycles. Clement et al. functionally characterized a highly expressed small secreted protein MiSSP8 from Laccaria bicolor, and showed that it helps establish ectomycorrhizal symbiosis. MiSSP8-RNAi mutants of L. bicolor are impaired in their mycorrhization activity and do not support the formation of the Hartig net (the network of fungal hyphae that surround the root and extends between cells). When expressed transiently in Nicotiana benthamiana MiSSP8 shows a co-localization with plasmodesmata. This work suggests that MiSSP8 has a possible dual role, the first in regulating hyphal formation and a second role related to plasmodesmata localization which remains to be elucidated. (Summary by Amey Redkar) bioRxiv.  10.1101/218131