A broadly conserved fungal alcohol oxidase (AOX) facilitates fungal invasion of plants

Alcohol oxidases (AOXs) are ecologically important enzymes that facilitate a number of plant-fungal interactions. Within Ascomycota they are primarily associated with methylotrophy, as a peroxisomal AOX catalysing the conversion of methanol to formaldehyde in methylotrophic yeast. In this study we demonstrate that AOX orthologues are phylogenetically conserved proteins that are common in the genomes of nonmethylotrophic, plant-associating fungi. Additionally, AOX orthologues are highly expressed during infection in a range of diverse pathosystems. To study the role of AOX in plant colonization, AOX knockout mutants were generated in the broad host range pathogen Sclerotinia sclerotiorum. Disease assays in soybean showed that these mutants had a significant virulence defect as evidenced by markedly reduced stem lesions and mortality rates. Chemical genomics suggested that SsAOX may function as an aromatic AOX, and growth assays demonstrated that Delta SsAOX is incapable of properly utilizing plant extract as a nutrient source. Profiling of known aromatic alcohols pointed towards the monolignol coniferyl alcohol (CA) as a possible substrate for SsAOX. As CA and other monolignols are ubiquitous among land plants, the presence of highly conserved AOX orthologues throughout Ascomycota implies that this is a broadly conserved protein used by ascomycete fungi during plant colonization.

Automated summary

Alcohol oxidases (AOXs) are ecologically important enzymes that play a significant role in plant-fungal interactions. This study found that AOX orthologues are commonly present in the genomes of nonmethylotrophic, plant-associating fungi and are highly expressed during infection. Knockout mutants of AOX in the pathogen Sclerotinia sclerotiorum showed reduced virulence in soybean. Chemical genomics suggested that SsAOX may function as an aromatic AOX and growth assays demonstrated its inability to properly utilize plant extract as a nutrient source.