Figure 1. MiSSP7 is required for root cell remodeling and hyphal penetration into the root apoplastic space. In the interaction between the ectomycorrhizal fungus Laccaria bicolor and poplar roots, the fungus surrounds the root and induces morphological changes in the epidermal cells and loosens the connections between the root cells such that fungal hyphae are able to penetrate in between the cells as seen in (A; arrow). When the production of the small secreted effector protein MiSSP7 of L. bicolor is reduced the same alterations to root epidermal cells are not observed nor are the connections between root cells loosened such that the fungal hyphae are not able to grow into the apoplastic space (B; arrows). Alterations to plant cell morphology and hyphal ingrowth are restored when MiSSP7 is expressed heterologously in poplar roots (C; arrow). All experiments were performed in triplicate to ensure reproducibility. Scale bar = 20 µm.