Zinc Metalloprotease SlMEP1: An Essential Factor Required for Fungal Virulence in Stemphylium lycopersici

<i>Stemphylium lycopersici</i> is the causal pathogen of the devastating tomato gray leaf spot with a wide range of alternative plant hosts. To mitigate its potential endemic in facility-cultivated tomatoes, novel disease control strategies should be attempted to minimize the use of chemical fungicides. In this study, we identified a metalloprotease from <i>S. lycopersici</i> genome and designated it as SlMEP1, as it appears to be a typical zinc metalloproteinase containing a WLM (WSS1-like metalloprotease) domain and a characteristic HEXXH motif, which we determined by analyzing its transcriptional profile and enzymatic functions. The transcription level of <i>SlMEP1</i> increased greatly during the fungal invasion of tomato leaves. The deletion of the <i>SlMEP1</i> gene from <i>S. lycopersici</i> hindered its mycelial growth and reduced its pathogenicity. An assessment of the functional dissection indicated that SlMEP1 induced cell collapse and inhibited the expression of the host chitinases, which consequently made tomato cells more susceptible to <i>S. lycopersici</i> and other pathogenic fungi.