Dissection of the host range of the fungal plant pathogen Alternaria alternata by modification of secondary metabolism

Kaoru Ito, Takayoshi Tanaka, Rieko Hatta, Mikihiro Yamamoto, Kazuya Akimitsu, Takashi Tsuge

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Abstract

The filamentous fungus Alternaria alternata contains seven pathogenic variants (pathotypes), which produce different host-specific toxins and cause diseases on different plants. The strawberry pathotype produces host-specific AF-toxin and causes Alternaria black spot of strawberry. This pathotype is also pathogenic to Japanese pear cultivars susceptible to the Japanese pear pathotype that produces AK-toxin. The strawberry pathotype produces two related molecular species, AF-toxins I and II: toxin I is toxic to both strawberry and pear, and toxin II is toxic only to pear. Previously, we isolated a cosmid clone pcAFT-1 from the strawberry pathotype that contains three genes involved in AF-toxin biosynthesis. Here, we have identified a new gene, designated AFTS1, from pcAFT-1. AFTS1 encodes a protein with similarity to enzymes of the aldo-ketoreductase superfamily. Targeted mutation of AFTS1 diminished the host range of the strawberry pathotype: ΔaftS1 mutants were pathogenic to pear, but not to strawberry, as is the Japanese pear pathotype. These mutants were found to produce AF-toxin II, but not AF-toxin I. These data represent a novel example of how the host range of a plant pathogenic fungus can be restricted by modification of secondary metabolism.

Original languageEnglish
Pages (from-to)399-411
Number of pages13
JournalMolecular Microbiology
Volume52
Issue number2
DOIs
Publication statusPublished - Apr 2004

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ASJC Scopus subject areas

  • Molecular Biology
  • Microbiology

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