P-113 - Lip3 is a phospholipid targeting lipase from Ustilago maydis contributing to its virulence

Ustilago maydis, the causative agent of corn smut, serves as a valuable model system for studying biotrophic interactions. Our study reveals increased secretory lipase activity in the infectious form of the fungus compared to its non-infectious form, indicating a crucial role for secreted lipases in fungal pathogenicity. Here, we have focused on Lip3, a secreted lipase, which exhibits differential expression during in-planta fungal growth. Notably, maize plants infected with ∆lip3 strains showed reduced infection symptom severity, along with delayed sporulation. The relative levels of certain lipids differ between SG200 WT and SG200Δlip3 infected plants, including phosphatidylglycerol, phosphatidylcholine, phosphatidic acid, etc. Lipid binding assays further confirmed an interaction of Lip3 with phosphatidic acid and phosphatidylserine. Using a phosphatidylserine targeting lactadherinC2 domain based biosensor, the differential distribution of phosphatidylserine within the biotrophic interface of SG200 WT and SG200Δlip3 infected plants was observed. We also detected significant levels of apoplast alkalinization in case of SG200 WT infection, that was absent in case of SG200Δlip3 infection. We believe this might be the result of differential activity of plasma membrane H⁺ ATPases in the presence of phosphatidylserine. Thus, through the regulation of phosphatidylserine distribution within the biotrophic interface, Lip3 can influence the apoplastic pH levels and hence, virulence.