title: Dissection of the host range of the fungal plant pathogen Alternaria alternata by modification of secondary metabolism.
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: Delta aftS1 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.
authors.affiliation: Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Ito
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Tanaka
authors.forename: Rieko
authors.initials: R
authors.lastname: Hatta
authors.forename: Mikihiro
authors.initials: M
authors.lastname: Yamamoto
authors.forename: Kazuya
authors.initials: K
authors.lastname: Akimitsu
authors.forename: Takashi
authors.initials: T
authors.lastname: Tsuge
mesh_terms: D000528:Alternaria / Q000235:genetics* / Q000472:pathogenicity*; D000595:Amino Acid Sequence; D015825:Chromosomes, Fungal; D003001:Cloning, Molecular; D003360:Cosmids; D031985:Fragaria / Q000382:microbiology*; D005638:Fruit / Q000382:microbiology*; D005656:Fungal Proteins / Q000235:genetics; D005800:Genes, Fungal; D007621:Karyotyping; D027845:Malus / Q000382:microbiology; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009183:Mycotoxins / Q000096:biosynthesis* / Q000235:genetics / Q000633:toxicity; D010935:Plant Diseases / Q000382:microbiology*; D010957:Plasmids; D031989:Pyrus / Q000382:microbiology; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014170:Transformation, Genetic
chemical_list: D005656:Fungal Proteins; D009183:Mycotoxins