Fubt, a Putative MFS Transporter, Promotes Secretion of Fusaric Acid in the Cotton Pathogen Fusarium oxysporum f. Sp. Vasinfectum

Fusaric acid (FA) is a key component in virulence and symptom development in cotton during infection by Fusarium oxysporum. A putative MFS transporter gene was identified upstream of the polyketide synthase gene responsible for the biosynthesis of FA. Disruption of the transporter gene, designated FUBT, resulted in loss of FA secretion, decrease in FA production, and a decrease in resistance to high concentrations of FA. Uptake of exogenous FA was unaffected in the disruption transformants, suggesting that FA enters the cell in Fusarium by an independent mechanism. Thus, FUBT is involved both in the extracellular transport of FA and in resistance of F. oxysporum to this non-specific toxin. A potential secondary resistance mechanism, the production of FA derivatives, was observed in FUBT deletion mutants. Molecular analysis of key biochemical processes in the production of FA may lead to future host-plant resistance to Fusarium pathogens.