Alcohol oxidase is a novel pathogenicity factor for Cladosporium fulvum, but aldehyde dehydrogenase is dispensable

Cladosporium fulvum is a mitosporic ascomycete pathogen of tomato. A study of fungal genes expressed during carbon starvation in vitro identified seve ral genes that were up regulated during growth in planta, These included ge nes predicted to encode acetaldehyde dehydrogenase (Aldh1) and alcohol oxid ase (Aox1), An Aldh1 deletion mutant was constructed. This mutant lacked al l detectable ALDH activity, had lost the ability to grow with ethanol as a carbon source, but was unaffected in pathogenicity Abx1 expression was indu ced by carbon starvation and during the later stages of infection. The alco hol oxidase enzyme activity has broadly similar properties (K-m values, sub strate specificity, pH, and heat stability) to yeast enzymes, Antibodies ra ised to Hansenula polymorpha alcohol oxidase (AOX) detected antigens in Wes tern blots of starved C. fulvum mycelium and infected plant material. Antig en reacting with the antibodies was localized to organelles resembling pero xisomes in starved mycelium and infected plants. Disruption mutants of Aox1 lacked detectable AOX activity and had markedly reduced pathogenicity as a ssayed by two different measures of fungal growth. These results identify a lcohol oxidase as a novel pathogenicity factor and are discussed in relatio n to peroxisomal metabolism of fungal pathogens during growth in planta.