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Function of Genes Encoding Acyl-CoA Synthetase and Enoyl-CoA Hydratase for Host-Selective ACT-Toxin Biosynthesis in the Tangerine Pathotype of Alternaria alternata

April 2009 , Volume 99 , Number  4
Pages  369 - 377

Y. Miyamoto, Y. Ishii, A. Honda, A. Masunaka, T. Tsuge, M. Yamamoto, K. Ohtani, T. Fukumoto, K. Gomi, T. L. Peever, and K. Akimitsu

First, second, third, fourth, seventh, eighth, ninth, and eleventh authors: United Graduate School and Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795 Japan; fifth author: Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601 Japan; sixth author: Faculty of Agriculture, Okayama University, Okayama 700-8530 Japan; and tenth author: Department of Plant Pathology, Washington State University, Pullman 99164-6430.

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Accepted for publication 13 October 2008.

The tangerine pathotype of Alternaria alternata produces host-selective ACT-toxin and causes Alternaria brown spot disease. Sequence analysis of a genomic cosmid clone identified a part of the ACTT gene cluster and implicated two genes, ACTT5 encoding an acyl-CoA synthetase and ACTT6 encoding an enoyl-CoA hydratase, in the biosynthesis of ACT-toxin. Genomic Southern blots demonstrated that both genes were present in tangerine pathotype isolates producing ACT-toxin and also in Japanese pear pathotype isolates producing AK-toxin and strawberry pathotype isolates producing AF-toxin. ACT-, AK-, and AF-toxins from these three pathotypes share a common 9,10-epoxy-8-hydroxy-9-methyl-decatrienoic acid moiety. Targeted gene disruption of two copies of ACTT5 significantly reduced ACT-toxin production and virulence. Targeted gene disruption of two copies of ACTT6 led to complete loss of ACT-toxin production and pathogenicity and a putative decatrienoic acid intermediate in ACT-toxin biosynthesis accumulated in mycelial mats. These results indicate that ACTT5 and ACTT6 are essential genes in ACT-toxin biosynthesis in the tangerine pathotype of A. alternata and both are required for full virulence of this fungus.

Additional keywords:citrus, host-specific toxin, toxin biosynthesis gene cluster.

© 2009 The American Phytopathological Society