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Multiple copies of AMT2 are prerequisite for the apple pathotype of Alternaria alternata to produce enough AM-toxin for expressing pathogenicity

  • Fungal Diseases
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Abstract

The apple pathotype of Alternaria alternata produces the cyclic depsipeptide AM-toxin and causes Alternaria blotch of apple. Previously, we cloned AMT2 from the apple pathotype as an orthologue of AFTS1, which is required for biosynthesis of the decatrienoic acid ester AF-toxin I of the strawberry pathotype. These genes were predicted to encode aldo-keto reductases involved in biosynthesis of a common precursor, 2-hydroxy-isovaleric acid, of AF-toxin I and AM-toxin. In this study, we analyzed the function of AMT2 in AM-toxin biosynthesis in the apple pathotype. DNA gel blot analysis of the apple pathotype strain IFO8984 with five restriction enzymes suggested that this strain has a single copy of AMT2 in the genome. However, gene disruption experiments showed that IFO8984 probably has three copies of AMT2. We made mutants having one or two copies of AMT2 disrupted. The single-copy mutants produced less AM-toxin than did the wild type and were still as pathogenic as the wild type. The two-copy mutants produced trace or undetectable amounts of AM-toxin and were markedly reduced in pathogenicity. Thus, AMT2 was verified to be required for AM-toxin biosynthesis and hence pathogenicity. The fact that the two-copy mutants have a remaining copy of AMT2 suggests that multiple copies of AMT2 are prerequisite for the pathogen to produce enough AM-toxin for full pathogenicity.

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Acknowledgments

We are grateful to Kazuya Akimitsu, Hirofumi Yoshioka, Kazuhito Kawakita, and Noriyuki Doke for valuable suggestions. This work was supported by Special Coordination Funds for Promoting Sciences from the Ministry of Education, Science, Sports, Culture and Technology of Japan and grants-in-aids from Japanese Society for Promotion of Sciences.

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Authors and Affiliations

  1. Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya, 464-8601, Japan

    Yoshiaki Harimoto, Takayoshi Tanaka & Takashi Tsuge

  2. Faculty of Agriculture, Tottori University, Tottori, 680-8553, Japan

    Motoichiro Kodama & Hiroshi Otani

  3. College of Agriculture, Okayama University, Okayama, 700-8530, Japan

    Mikihiro Yamamoto

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  1. Yoshiaki Harimoto
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  2. Takayoshi Tanaka
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  3. Motoichiro Kodama
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  4. Mikihiro Yamamoto
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  5. Hiroshi Otani
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  6. Takashi Tsuge
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Correspondence to Takashi Tsuge.

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Harimoto, Y., Tanaka, T., Kodama, M. et al. Multiple copies of AMT2 are prerequisite for the apple pathotype of Alternaria alternata to produce enough AM-toxin for expressing pathogenicity. J Gen Plant Pathol 74, 222–229 (2008). https://doi.org/10.1007/s10327-008-0089-1

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