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A Zinc-Finger-Family Transcription Factor, AbVf19, Is Required for the Induction of a Gene Subset Important for Virulence in Alternaria brassicicola

April 2012 , Volume 25 , Number  4
Pages  443 - 452

Akhil Srivastava,1 Robin A. Ohm,2 Lindsay Oxiles,1 Fred Brooks,1 Christopher B. Lawrence,3 Igor V. Grigoriev,2 and Yangrae Cho1

1Plant and Environmental Protection Sciences, University of Hawaii at Manoa, 3190 Maile Way, St. John 317, Honolulu 96822, U.S.A.; 2United States Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA 94598, U.S.A.; and 3Virginia Bioinformatics Institute and Department of Biological Sciences, Virginia Tech, Blacksburg 24061, U.S.A.

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Accepted 2 December 2011.

Alternaria brassicicola is a successful saprophyte and necrotrophic plant pathogen with a broad host range within the family Brassicaceae. It produces secondary metabolites that marginally affect virulence. Cell wall–degrading enzymes (CDWE) have been considered important for pathogenesis but none of them individually have been identified as significant virulence factors in A. brassicicola. In this study, knockout mutants of a gene, AbVf19, were created and produced considerably smaller lesions than the wild type on inoculated host plants. The presence of tandem zinc-finger domains in the predicted amino acid sequence and nuclear localization of AbVf19-reporter protein suggested that it was a transcription factor. Gene expression comparisons using RNA-seq identified 74 genes being downregulated in the mutant during a late stage of infection. Among the 74 downregulated genes, 28 were putative CWDE genes. These were hydrolytic enzyme genes that composed a small fraction of genes within each family of cellulases, pectinases, cutinases, and proteinases. The mutants grew slower than the wild type on an axenic medium with pectin as a major carbon source. This study demonstrated the existence and the importance of a transcription factor that regulates a suite of genes that are important for decomposing and utilizing plant material during the late stage of plant infection.

© 2012 The American Phytopathological Society