The tomato xylem sap protein XSP10 is required for full susceptibility to Fusarium wilt disease

XSP10 is an abundant 10 kDa protein found in the xylem sap of tomato. The protein displays structural similarity to plant lipid transfer proteins (LTPs). LTPs are involved in various physiological processes, including disease resistance, and some are able to bind and transfer diverse lipid molecules. XSP10 abundance in xylem sap declines upon infection with Fusarium oxysporum f. sp. lycopersici (Fol), implying involvement of XSP10 in the plant-pathogen interaction. Here, the biochemical characterization of XSP10 with respect to fatty acid-binding properties is reported; a weak but significant binding to saturated fatty acids was found. Furthermore, XSP10-silenced tomato plants were engineered and it was found that these plants exhibited reduced disease symptom development upon infection with a virulent strain of Fol. Interestingly, the reduced symptoms observed did not correlate with an altered expression profile for known reporter genes of plant defence (PR-1 and WIPI). This work demonstrates that XSP10 has lipid-binding properties and is required for full susceptibility of tomato to Fusarium wilt.