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Role of the Host-Selective ACT-Toxin Synthesis Gene ACTTS2 Encoding an Enoyl-Reductase in Pathogenicity of the Tangerine Pathotype of Alternaria alternata

February 2010 , Volume 100 , Number  2
Pages  120 - 126

Naoya Ajiro, Yoko Miyamoto, Akira Masunaka, Takashi Tsuge, Mikihiro Yamamoto, Kouhei Ohtani, Takeshi Fukumoto, Kenji Gomi, Tobin L. Peever, Yuriko Izumi, Yasuomi Tada, and Kazuya Akimitsu

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

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Accepted for publication 7 October 2009.

The tangerine pathotype of Alternaria alternata produces host-selective ACT-toxin and causes Alternaria brown spot disease of tangerines and tangerine hybrids. Sequence analysis of a genomic BAC clone identified a previously uncharacterized portion of the ACT-toxin biosynthesis gene cluster (ACTT). A 1,034-bp gene encoding a putative enoyl-reductase was identified by using rapid amplification of cDNA ends and polymerase chain reaction and designated ACTTS2. Genomic Southern blots demonstrated that ACTTS2 is present only in ACT-toxin producers and is carried on a 1.9 Mb conditionally dispensable chromosome by the tangerine pathotype. Targeted gene disruption of ACTTS2 led to a reduction in ACT-toxin production and pathogenicity, and transcriptional knockdown of ACTTS2 using RNA silencing resulted in complete loss of ACT-toxin production and pathogenicity. These results indicate that ACTTS2 is an essential gene for ACT-toxin biosynthesis in the tangerine pathotype of A. alternata and is required for pathogenicity of this fungus.

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

© 2010 The American Phytopathological Society