Trehalose is required for stress resistance and virulence of the Basidiomycota plant pathogen Ustilago maydis

Trehalose is an important disaccharide that can be found in bacteria, fungi, invertebrates and plants. In some Ascomycota fungal plant pathogens, the role of trehalose was recently studied and shown to be important for conferring protection against several environmental stresses and for virulence. In most of the fungi studied, two enzymes are involved in the synthesis of trehalose: trehalose-6-phosphate synthase (Tps1) and trehalose-6-phosphate phosphatase (Tps2). To study the role of trehalose in virulence and stress response in the Basidiomycota maize pathogen Ustilago maydis, Delta tps2 deletion mutants were constructed. These mutants did not produce trehalose as confirmed by HPLC analysis, showing that the single gene disruption impaired its biosynthesis. The mutants displayed increased sensitivity to oxidative, heat, acid, ionic and osmotic stresses as compared to the wild-type strains. Virulence of Atios2 mutants to maize plants was extremely reduced compared to wild-type strains, possibly due to reduced capability to deal with the hostile host environment. The phenotypic traits displayed by Delta tps2 strains were fully restored to wild-type levels when complemented with the endogenous UmTPS2 gene, or a chimeric construct having the Saccharomyces cerevisiae TPS2 ORF. This report demonstrates the presence of a single biosynthetic pathway for trehalose, and its importance for virulence in this model Basidiomycota plant pathogen.