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ACTTS3 Encoding a Polyketide Synthase Is Essential for the Biosynthesis of ACT-Toxin and Pathogenicity in the Tangerine Pathotype of Alternaria alternata

April 2010 , Volume 23 , Number  4
Pages  406 - 414

Y. Miyamoto,1 A. Masunaka,1 T. Tsuge,2 M. Yamamoto,3 K. Ohtani,1 T. Fukumoto,1 K. Gomi,1 T. L. Peever,4 Y. Tada,1 K. Ichimura,1 and K. Akimitsu1

1Faculty of Agriculture and Gene Research Center, Kagawa University, Miki, Kagawa 761-0795, Japan; 2Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan; 3Faculty of Agriculture, Okayama University, Okayama 700-8530, Japan; 4Department of Plant Pathology, Washington State University, Pullman 99164-6430, U.S.A.

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Accepted 30 November 2009.

The tangerine pathotype of Alternaria alternata produces host-selective ACT-toxin and causes Alternaria brown spot disease of tangerine and tangerine hybrids. Sequence analysis of a genomic BAC clone identified part of the ACT-toxin TOX (ACTT) gene cluster, and knockout experiments have implicated several open reading frames (ORF) contained within the cluster in the biosynthesis of ACT-toxin. One of the ORF, designated ACTTS3, encoding a putative polyketide synthase, was isolated by rapid amplification of cDNA ends and genomic/reverse transcription-polymerase chain reactions using the specific primers designed from the BAC sequences. The 7,374-bp ORF encodes a polyketide synthase with putative β-ketoacyl synthase, acyltransferase, methyltransferase, β-ketoacyl reductase, and phosphopantetheine attachment site domains. Genomic Southern blots demonstrated that ACTTS3 is present on the smallest chromosome in the tangerine pathotype of A. alternata, and the presence of ACTTS3 is highly correlated with ACT-toxin production and pathogenicity. Targeted gene disruption of two copies of ACTTS3 led to a complete loss of ACT-toxin production and pathogenicity. These results indicate that ACTTS3 is an essential gene for ACT-toxin biosynthesis in the tangerine pathotype of A. alternata and is required for pathogenicity of this fungus.

© 2010 The American Phytopathological Society