ARS | Publication request: Nonhost-specific phytotoxicity of the polyketide-derived toxin solanapyrone A produced by Ascochyta rabiei and Alternaria solani

Submitted to: Fungal Genetics Reports
Publication Type: Abstract Only
Publication Acceptance Date: February 25, 2013
Publication Date: March 11, 2013
Citation: Kim, W., Tymon, L., Johnson, D., Chen, W. 2013. Nonhost-specific phytotoxicity of the polyketide-derived toxin solanapyrone A produced by Ascochyta rabiei and Alternaria solani. Fungal Genetics Reports. 60 (Suppl): 615.

Technical Abstract: Solanapyrone A is a polyketide-derived metabolite produced by Ascochyta rabiei and Alternaria solani, which are the most destructive necrotrophic pathogens of chickpea and potato/tomato, respectively. They belong to the Order Pleosporales within the Class Dothideomycetes, but are phylogenetically distantly-related. All isolates of the two fungi tested so far are capable of producing solanapyrone A in synthetic media, which may imply that it is indispensable for their life cycle. However, very little is known about the genetics of solanapyrone A production and its role in pathogenesis and their life cycle. Recently, a solanapyrone biosynthesis gene cluster was identified in Al. solani. Six genes (Sol1 - Sol6) form the gene cluster, spaning about 20 kb of the genome. Among them, Sol5 gene encodes a Diel-Alderase which catalyzes the final step of solanapyrone biosynthesis pathway. Knockout of the Sol5 gene in both A. rabiei and Al.solani resulted in the production of three compounds, presumably solanapyrone precursors, instead of solanapyrone A. Colony of sol5 mutants showed expansive growth in agar medium until covering the entire plates, in contrast to restricted growth colony of their corresponding wild-type progenitors. The restricted growth of the wild type strains is likely due to solanapyrone toxicity. Phytotoxicity of solanapyrone A was examined with various plant species including their natural host plants. Solanapyrone A produced similar size of necrotic lesions on all plant species tested. On the other hand, one of the putative solanapyrone precursors with the same molecular weight of solanapyrone A caused much smaller lesions only around the wounds of application sites. These results indicate that solanapyrone A is a nonhost-specific phytotoxin because it caused a similar degree of lesions on host and nonhost species.