Fusarium oxysporum Adh1 has dual fermentative and oxidative functions and is involved in fungal virulence in tomato plants

► An alcohol dehydrogenase gene, adh1, was identified in the fungus Fusarium oxysporum. ► adh1 is highly expressed in mycelia grown in PDB medium under hypoxic conditions. ► Allyl alcohol-resistant mutants showed alterations in adh1 leading to Adh1 deficiency. ► Adh1 has fermentative and oxidative functions, depending on culture conditions. ► Adh1 is required for the development of full fungal virulence. An alcohol dehydrogenase gene, adh1, has been identified in the vascular wilt fungus Fusarium oxysporum f. sp. lycopersici. Reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that adh1 is highly expressed in mycelia grown in potato dextrose liquid medium (PDB) under hypoxic conditions, as compared to mycelia grown under aerobic conditions. One spontaneous allyl alcohol-resistant (Ally R) mutant exhibited insertion of an incomplete F. oxysporum transposable element, while another mutant contained a short (13 nucleotide) deletion, in both cases interrupting the coding region of the adh1 gene. These mutations caused deficiency in Adh activity due to loss of the main constitutive isoform of Adh1, as well as alteration of different physiological parameters related to carbon and energy metabolism, including the ability to use ethanol as a carbon source under aerobic conditions; impaired growth under hypoxic conditions with glucose as the carbon source; and diminished production of ethanol in glucose-containing medium. Interestingly, the adh1 mutations resulted in a significant delay in fungal disease development in tomato plants. Complementation with the wild-type adh1 allele repaired all defects caused by mutation, indicating that the product of the adh1 gene has dual enzymatic functions (fermentative and oxidative), depending on culture conditions, and is also required for full fungal virulence.