SnPKS19Encodes the Polyketide Synthase for Alternariol Mycotoxin Biosynthesis in the Wheat Pathogen Parastagonospora nodorum

Abstract

ABSTRACTAlternariol (AOH) is an important mycotoxin from theAlternariafungi. AOH was detected for the first time in the wheat pathogenParastagonospora nodorumin a recent study. Here, we exploited reverse genetics to demonstrate that SNOG_15829 (SnPKS19), a close homolog ofPenicillium aethiopicumnorlichexanthone (NLX) synthase genegsfA, is required for AOH production. We further validate thatSnPKS19is solely responsible for AOH production by heterologous expression inAspergillus nidulans. The expression profile ofSnPKS19based on previousP. nodorummicroarray data correlated with the presence of AOHin vitroand its absencein planta. Subsequent characterization of the ΔSnPKS19mutants showed thatSnPKS19and AOH are not involved in virulence and oxidative stress tolerance. Identification and characterization of theP. nodorumSnPKS19cast light on a possible alternative AOH synthase gene inAlternaria alternataand allowed us to survey the distribution of AOH synthase genes in other fungal genomes. We further demonstrate that phylogenetic analysis could be used to differentiate between AOH synthases and the closely related NLX synthases. This study provides the basis for studying the genetic regulation of AOH production and for development of molecular diagnostic methods for detecting AOH-producing fungi in the future.