|KIM, WONYONG - Washington State University
|PARK, JEONG-JI - Washington State University
|GANG, DAVID - Washington State University
|PEEVER, TOBIN - Washington State University
Submitted to: Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2017
Publication Date: 1/21/2017
Citation: Kim, W., Park, J., Dugan, F.M., Gang, D., Vandemark, G.J., Peever, T., Chen, W. 2017. Production of the antibiotic secondary metabolite solanapyrone A by the fungal plant pathogen Ascochyta rabiei during fruiting body formation in saprobic growth. Environmental Microbiology. 19(5):1822-1835. https://doi.org/10.1111/1462-2920.13673.
Interpretive Summary: The plant pathogen Ascochyta rabiei causes the destructive disease Ascochyta blight of chickpea and also produces secondary metabolites solanapyrones that are toxic to plants and other microorganisms. Early on scientists assumed that the toxins are virulence factors in causing Ascochyta blight. However, our recent studies have shown that the solanapyrone toxins are not required for pathogenicity. Results obtained in this study have shown that wild type A. rabiei effectively suppressed the growth of other competing fungi usually found on chickpea straw. The toxin solanapyrone A was directly detected in the inhibitory zone, and showed significant antifungal activities. These results suggest that solanapyrone A plays an important role for competition and presumably the survival of the fungus during the overwintering period, allowing it to successfully compete with other saprophytic microorganisms and survive in natural habitats.
Technical Abstract: Fungi are noted for production of a diverse array of secondary metabolites, many of which are of pharmacological importance. However, the biological roles of these molecules during the fungal life cycle in nature remain elusive. Solanapyrones are polyketide-derived secondary metabolites produced by diverse fungal species including the chickpea blight pathogen, Ascochyta rabiei. Chemical profiling and gene expression studies showed that solanapyrone A was specifically produced during its saprobic growth, but not during the parasitic growth of A. rabiei. Expression of the gene encoding the last step enzyme for solanapyrone biosynthesis was specifically associated with development of the asexual fruiting bodies. In confrontation assays with saprobic fungi that were commonly found in chickpea debris left in fields, A. rabiei effectively suppressed the growth of the competing fungi. Solanapyrone A was directly detected in the inhibitory zone, and showed significant antifungal activities. These results suggest that solanapyrone A plays an important role for competition and presumably the survival of the fungus during the overwintering period.