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Deletion of all Cochliobolus heterostrophus Monofunctional Catalase-Encoding Genes Reveals a Role for One in Sensitivity to Oxidative Stress but None with a Role in Virulence

November 2003 , Volume 16 , Number  11
Pages  1,013 - 1,021

Barbara Robbertse , 1 O. C. Yoder , 1 Anita Nguyen , 1 Conrad L. Schoch , 2 and B. Gillian Turgeon 2

1Former Torrey Mesa Research Institute, 3115 Merryfield Row, San Diego, CA 92122, U.S.A.; 2Department of Plant Pathology, Cornell University, Ithaca, NY 14853, U.S.A.

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Accepted 19 June 2003.

The genome of the maize pathogen Cochliobolus heterostrophus encodes three unlinked monofunctional catalase-encoding (CAT) genes that singly or in combination could offer protection against the harmful effects of oxidative stress. Phylogenetic analysis placed the CAT2 and CAT3 proteins in a cluster with large subunit catalases (CAT3 has a secretory signal sequence and was grouped with known secreted catalases), whereas CAT1 clustered with small subunit catalases. Single, double, and triple cat mutants were created and screened for sensitivity to hydrogen peroxide and altered virulence on maize. All mutants deficient in CAT3 had enhanced sensitivity to hydrogen peroxide, as compared with wild type or with mutants deficient in CAT1, CAT2, or both. All catalase-deficient mutants had normal virulence to maize. Thus, the secreted CAT3 protein protects the fungus from oxidative stress during vegetative growth, but members of this enzyme family, alone or in combination, are not essential for virulence.

Additional keywords: fungi, genome sequence, pathogenicity.

© 2003 The American Phytopathological Society