Title: Identification of solanapyrone biosynthesis genes and generation of solanapyrone-deficient mutants in Ascochyta rabiei Authors
Submitted to: International Ascochyta Workshop
Publication Type: Abstract Only
Publication Acceptance Date: March 4, 2012
Publication Date: April 20, 2012
Citation: Kim, W., Akamatsu, H.O., Peever, T., Vandemark, G.J., Chen, W. 2012. Identification of solanapyrone biosynthesis genes and generation of solanapyrone-deficient mutants in Ascochyta rabiei. International Ascochyta Workshop. Page 52. Technical Abstract: Ascochyta rabiei, the causal agent of Ascochyta blight of chickpea, produces solanapyrone toxins which are toxic to chickpea. However, very little is known about the genetics of toxin production and the role of the toxins in pathogenesis. In the present study, solanapyrone biosynthesis genes in A. rabiei were identified using PCR primers designed to solanapyrone biosynthesis genes from Alternaria solani, a fungus that produces the same toxins. Six genes (sol1 - sol6) form the solanapyrone biosynthesis gene cluster in A. solani. The sol5 gene, encoding solanapyrone synthase catalyzing the final step of solanapyrone biosynthesis, was targeted in A. rabiei to generate toxin-deficient mutants. Gene replacement mutants of four A. rabiei isolates, AR628, AR20, AR19, and GFP-expressing AR628 (AR628G), produced no solanapyrones in liquid culture. The precursor of solanapyrones, prosolanapyrone III, accumulated in culture media of the gene replacement mutants, but was not toxic to chickpea. The toxin-deficient mutants showed increased radial growth and reduced colony pigmentation relative to wild-type on solid agar media. Virulence of the toxin-deficient mutants was not significantly different from wild-type progenitor isolates in chickpea inoculation assays. Using the GFP-strain AR628G and its toxin-deficient mutant, colonization and reproduction of the fungus on chickpea plants was visualized under a fluorescent microscope. No significant differences in pre-penetration behavior, penetration and colonization ability were found between toxin-producing and toxin-deficient strains. These results demonstrate that solanapyrone is not essential for the infection processes such as penetration and colonization of host tissues.