title: Functional Analyses of the Diels-Alderase Gene sol5 of Ascochyta rabiei and Alternaria solani Indicate that the Solanapyrone Phytotoxins Are Not Required for Pathogenicity.
abstract: Ascochyta rabiei and Alternaria solani, the causal agents of Ascochyta blight of chickpea (Cicer arietinum) and early blight of potato (Solanum tuberosum), respectively, produce a set of phytotoxic compounds including solanapyrones A, B, and C. Although both the phytotoxicity of solanapyrones and their universal production among field isolates have been documented, the role of solanapyrones in pathogenicity is not well understood. Here, we report the functional characterization of the sol5 gene, which encodes a Diels-Alderase that catalyzes the final step of solanapyrone biosynthesis. Deletion of sol5 in both Ascochyta rabiei and Alternaria solani completely prevented production of solanapyrones and led to accumulation of the immediate precursor compound, prosolanapyrone II-diol, which is not toxic to plants. Deletion of sol5 did not negatively affect growth rate or spore production in vitro, and led to overexpression of the other solanapyrone biosynthesis genes, suggesting a possible feedback regulation mechanism. Phytotoxicity tests showed that solanapyrone A is highly toxic to several legume species and Arabidopsis thaliana. Despite the apparent phytotoxicity of solanapyrone A, pathogenicity tests showed that solanapyrone-minus mutants of Ascochyta rabiei and Alternaria solani were equally virulent as their corresponding wild-type progenitors, suggesting that solanapyrones are not required for pathogenicity.
authors.affiliation: 1 Department of Plant Pathology.
authors.forename: Wonyong
authors.initials: W
authors.lastname: Kim
authors.affiliation: 2 Department of Chemistry, and.
authors.forename: Chung-Min
authors.initials: CM
authors.lastname: Park
authors.affiliation: 3 Institute of Biological Chemistry, Washington State University, Pullman 99164, U.S.A.; and.
authors.forename: Jeong-Jin
authors.initials: JJ
authors.lastname: Park
authors.affiliation: 1 Department of Plant Pathology.
authors.forename: Hajime O
authors.initials: HO
authors.lastname: Akamatsu
authors.affiliation: 1 Department of Plant Pathology.
authors.forename: Tobin L
authors.initials: TL
authors.lastname: Peever
authors.affiliation: 2 Department of Chemistry, and.
authors.forename: Ming
authors.initials: M
authors.lastname: Xian
authors.affiliation: 3 Institute of Biological Chemistry, Washington State University, Pullman 99164, U.S.A.; and.
authors.forename: David R
authors.initials: DR
authors.lastname: Gang
authors.affiliation: 1 Department of Plant Pathology.|4 United States Department of Agriculture-Agricultural Research Service, Grain Legume Genetics and Physiology Research Unit, Washington State University, Pullman.
authors.forename: George
authors.initials: G
authors.lastname: Vandemark
authors.affiliation: 1 Department of Plant Pathology.|4 United States Department of Agriculture-Agricultural Research Service, Grain Legume Genetics and Physiology Research Unit, Washington State University, Pullman.
authors.forename: Weidong
authors.initials: W
authors.lastname: Chen