Basic xylanases from the fungal tomato pathogen Fusarium oxysporum f.sp. lycopersici

We purified four xylan-degrading enzymes (endo-xylanases: EC 3.2.1.8) produced in vitro by the fungal pathogen Fusarium oxysporum f.sp. lycopersici (Fol). The xylanases were resolved by a combination of ion exchange and hydrophobic interaction chromatography, and preparative native-PAGE electrophoresis. They had molecular masses of 38, 34, 22 and 19 kDa, pI higher than 9.3, endo-cleavage mechanism and maximal activity at pH 6.0 and 45°C. Comparison of the reaction products showed differences in the cleavage mechanism of two of the xylanases. In addition their role as possible elicitors of stress and defence responses was examined in preliminary assays. Xylanases from a variety of pathogenic and nonpathogenic fungi have been described as inducers of plant stress and defence responses. A role as elicitors of active defence mechanisms was suggested for the ethylene biosynthesis-inducing xylanase from T. viride (EIX) and EIX-like enzymes from a variety of pathogenic fungi. In spite of the homologies with the EIX from T. viride none of the Fol xylanases examined by us were antigenically related to it. Furthermore, they showed no EIX-like eliciting activity on cell culture suspensions or intact tomato leaflets in our tests. Therefore their role as recognition factors is not established in our experimental model.