Mapping ortholog-restricted ligandable cysteines in the wheat pathogen Zymoseptoria tritici

Zymoseptoria (Z.) tritici is the fungal phytopathogen responsible for Septoria tritici leaf blotch (STB), the main foliar disease of wheat. Fungicides mitigate crop loss caused by STB, but multidrug-resistant Z. tritici strains pose a major threat to the global food supply and underscore the need to identify new fungicidal targets. Here, we use activity-based protein profiling to generate a covalent ligandability map of Z. tritici, leading to the discovery of cysteines in a diverse set of essential proteins that are targeted by stereochemically defined, electrophilic small molecules (stereoprobes). We identify stereoprobes that display nucleotide-dependent reactivity with an ortholog-restricted cysteine in the GTPase SAR1, leading to accumulation of this protein and other COPII components at apparent ER exit sites and corresponding impairments in Z. tritici growth. Our findings thus expand the scope of ligandable, essential proteins in Z. tritici and illuminate opportunities to selectively target this destructive plant pathogen.