Structural and functional complexity of the genomic region controlling AK-toxin biosynthesis and pathogenicity in the Japanese pear pathotype of Alternaria alternata.
The Japanese pear pathotype of Alternaria alternata produces host-specific AK-toxin and causes black spot of Japanese pear. Previously, a cosmid clone, pcAKT-1, was isolated that contains two genes, AKT1 and AKT2, within a 5.0-kb region required for AK-toxin biosynthesis. The wild-type strain has multiple, nonfunctional copies of these genes. In the present study, two additional genes, AKTR-1 and AKT3-1, downstream of AKT2 were identified. Transformation of the wild type with AKTR-1- and AKT3-1-targeting vectors produced toxin-deficient (Tox-), nonpathogenic mutants. DNA gel blot analysis, however, demonstrated that the fragments targeted in Tox- mutants were different from those containing AKTR-1 and AKT3-1 on the transforming vectors. A cosmid clone, pcAKT-2, containing the targeted DNA was isolated and shown to carry two genes, AKTR-2 and AKT3-2, with high similarity to AKTR-1 and AKT3-1, respectively. Transcripts from not only AKTR-2 and AKT3-2 but also AKTR-1 and AKT3-1 were found in the wild type. DNA gel blot analysis with pulsed-field gel electrophoresis showed that AKT1, AKT2, AKT3, and AKTR and their homologues are on a single chromosome. These results indicate the structural and functional complexity of the genomic region controlling AK-toxin biosynthesis.
Tanaka
A
A
Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Japan.
Tsuge
T
T
D000528:Alternaria / Q000235:genetics / Q000472:pathogenicity*; D000595:Amino Acid Sequence; D001483:Base Sequence; D004271:DNA, Fungal; D005231:Fatty Acids, Unsaturated / Q000096:biosynthesis* / Q000502:physiology*; D018390:Gene Targeting; D008969:Molecular Sequence Data; D009154:Mutation; D016366:Open Reading Frames; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000096:biosynthesis* / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D014197:Trees / Q000382:microbiology*
D004271:DNA, Fungal; D005231:Fatty Acids, Unsaturated; D010649:Phenylalanine; C089064:AK-toxin II