here - First Legume Society Conference (LSC1)

Book of Abstracts First Legume Society Conference 2013: A Legume Odyssey Novi Sad, Serbia, 9-11 May 2013
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Investigating the role of solanapyrone toxins in Ascochyta blight using toxin-deficient
mutants of Ascochyta rabiei
W Kim 1 , HO Akamatsu 1 , TL Peever 1 , GJ Vandemark 1,2 , W Chen 1,2
1 Department of Plant Pathology, Washington State University, Pullman, USA
2 USDA-ARS, Grain Legume Genetic and Physiology Research Unit, Washington State University, Pullman,
USA
Ascochyta rabiei, the causal agent of Ascochyta blight of chickpea, produces solanapyrone toxins
(solanapyrone A, B and C). However, very little is known about the genetics of toxin production
and the role of the toxins in pathogenesis. Generating mutants deficient in the toxin biosynthesis
would provide information on the role of the toxins during infection processes. Partial genomic
sequences of the solanapyrone biosynthesis gene cluster in A.rabiei were identified, based on the
homologous sol gene cluster (sol1 - sol6) in Alternaria solani, which also produces the same toxins.
The sol5 and sol4 genes which encode solanapyrone synthase and a fungal specific transcription
factor, respectively, were targeted to generate toxin-deficient mutants. Deletion of either the sol4
or the sol5 gene abolished production of solanopayrone toxins. The sol5-deletion mutants
produced no solanapyrone toxxins and accumulated the precursor prosolanapyrone II, whereas
thesol4-deletion mutants did not produce either solanapyrone toxins or the prosolanapyrone II.
Solanopyrone toxins, but not the prosolanopyrone II precursor, showed toxicity to chickpea.
Both the mutants showed normal growth patterns and conidiation in culture. Virulence of the
toxin-deficient mutants was examined in pathogenicity assay using two-week old chickpea
seedlings. Both sol4 and sol5 mutants showed no reduction in virulence, producing disease similar
to the disease levels produced by wild-type strain. These findings indicate that sol4 gene is a
positive regulator for solanapyrone biosynthesis, and that solanapyrone is not essential for the
chickpea seedling infection.
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