The multifunctional beta-oxidation enzyme is required for full symptom development by the biotrophic maize pathogen Ustilago maydis

The transition from yeast-like to filamentous growth in the biotrophic fungal phytopathogen Ustilago maydis is a crucial event for pathogenesis. Previously, we showed that fatty acids induce filamentation in U. maydis and that the resulting hyphal cells resemble the infectious filaments observed in planta. To explore the potential metabolic role of lipids in the morphological transition and in pathogenic development in host tissue, we deleted the mfe2 gene encoding the multifunctional enzyme that catalyzes the second and third reactions in beta-oxidation of fatty acids in peroxisomes. The growth of the strains defective in mfe2 was attenuated on long-chain fatty acids and abolished on very-long-chain fatty acids. The mfe2 gene was not generally required for the production of filaments during mating in vitro, but loss of the gene blocked extensive proliferation of fungal filaments in planta. Consistent with this observation, mfe2 mutants exhibited significantly reduced virulence in that only 27% of infected seedlings produced tumors compared to 88% tumor production upon infection by wild-type strains. Similarly, a defect in virulence was observed in developing ears upon infection of mature maize plants. Specifically, the absence of the mfe2 gene delayed the development of teliospores within mature tumor tissue. Overall, these results indicate that the ability to utilize host lipids contributes to the pathogenic development of U. maydis.