N-Glycosylation Mediates Smut Effector Adaptation Toward a Host Pectin Methylesterase Inhibitor

The demethylation status of pectin, a major plant cell wall polysaccharide, is regulated by pectin methylesterases (PMEs) and their endogenous inhibitors (PMEIs). While PME-mediated removal of methyl groups increases pectin susceptibility to enzymatic degradation and facilitates wall remodeling, this process is suppressed by PMEIs to strengthen the wall, preventing pathogen invasion. How biotrophic pathogens overcome this inhibitory defense remains unclear. Here, we demonstrate how N-glycosylation serves as a post-translational mechanism that pre-shapes a conserved smut effector, directing its adaptation toward a host-specific PMEI to facilitate colonization. We identify the Ustilago maydis N-glycosylated effector Nge1, which interacts with two host inhibitors, PMEI45 and PMEI46, to suppress their inhibitory function. This release of PME activity leads to highly demethylated pectin in the host cell wall that is prone to degradation, likely driving the cell wall loosening favored by pathogens. Crucially, we show that N-glycosylation of Nge1 is essential for its interaction with PMEI45, whereas the interaction with PMEI46 is glycosylation-independent. Engineering N-glycosylation sites into a naturally non-glycosylated Nge1 ortholog restored its ability to neutralize host PMEIs and functionally complement the U. maydis Δnge1 mutant. Our findings reveal that smut fungi utilize post-translational glycan modifications to fine-tune effector specificity, allowing them to overcome host-adapted PMEIs and manipulate plant cell wall dynamics in an ongoing plant-fungal interplay.