Although ectomycorrhizal symbioses are widespread and important for plant health in many ecosystems, little is known about the genetic requirements for fungal differentiation during mycorrhizal development. In the October issue, Doré and colleagues report T-DNA mutagenesis of the basidiomycete Hebeloma cylindrosporum, resulting in identification of the gene HcMycE1. Disruption of this gene blocks fungal ability to differentiate fungal sheath and Hartig net structures. Identifying HcMycE1 sets the stage for genetic dissection of the fungal side of ectomycorrhizal symbioses. View Article