A kiwellin disarms the metabolic activity of a secreted fungal virulence factor

Fungi-induced plant diseases affect global food security and plant ecology. The biotrophic fungus Ustilago maydis causes smut disease in maize ( Zea mays ) plants by secreting numerous virulence effectors that reprogram plant metabolism and immune responses 1 , 2 . The secreted fungal chorismate mutase Cmu1 presumably affects biosynthesis of the plant immune signal salicylic acid by channelling chorismate into the phenylpropanoid pathway 3 . Here we show that one of the 20 maize-encoded kiwellins ( Zm KWL1) specifically blocks the catalytic activity of Cmu1. Zm KWL1 hinders substrate access to the active site of Cmu1 through intimate interactions involving structural features that are specific to fungal Cmu1 orthologues. Phylogenetic analysis suggests that plant kiwellins have a versatile scaffold that can specifically counteract pathogen effectors such as Cmu1. We reveal the biological activity of a member of the kiwellin family, a widely conserved group of proteins that have previously been recognized only as important human allergens. A kiwellin protein in maize is found to inhibit the activity of the secreted enzyme chorismate mutase from a maize-infecting pathogenic fungus, suggesting a role for kiwellins in plant immunity.