Blast fungus unconventional effector secretion sorting requires pre-Golgi compartment protein MoGrh1

Brefeldin A (BFA)-resistant unconventional protein secretion (UPS) is documented in cellular systems across taxa and has roles in disease, but mechanistic details remain sparse. The blast fungus Magnaporthe oryzae uses Golgi-bypass UPS to deploy plant immunity-suppressing cytoplasmic effector proteins into host rice cells to establish infection. However, few M. oryzae UPS components are known, and connections to other cellular processes are undefined. Here, using live-cell imaging of M. oryzae mutant strains, we show that MoGrh1, a resident of the pre-Golgi, BFA-resistant ER-Golgi intermediate compartment (ERGIC), is required for UPS cargo sorting under the autophagy-inducing conditions of early host cell colonization. The loss of MoGRH1 abolished UPS, with cytoplasmic effectors misrouted through a BFA-sensitive secretion pathway instead. Treatment with autophagy-suppressing -ketoglutarate, a preferred carbon source, reconstituted unconventional secretion in {Delta}grh1, restoring fungal growth in host cells. We conclude that MoGrh1 supports UPS cargo sorting under the nutrient-limiting conditions of early host cell infection, linking the ERGIC and autophagy to disease-causing effector secretion in a devastating plant pathogen.