title: Spontaneous loss of a conditionally dispensable chromosome from the Alternaria alternata apple pathotype leads to loss of toxin production and pathogenicity.
abstract: The Alternaria alternata apple pathotype causes Alternaria blotch of susceptible apple cultivars through the production of a cyclic peptide, host-specific toxin, AM-toxin. We recently cloned a cyclic peptide synthetase gene, AMT, whose product catalyzes the production of AM-toxin and showed that it resides on chromosomes of 1.8 Mb or less, depending on the A. alternata apple pathotype strain. Reverse transcriptase (RT)-PCR, using primers specific to AMT, on laboratory sub-cultured strains previously shown to produce AM-toxin, identified one isolate that did not express the gene. A leaf necrosis bioassay confirmed an AM-toxin-minus phenotype. However, an original isolate of this strain which had not undergone sub-culture gave a positive result by both RTPCR and bioassay. Contour-clamped homogeneous electric field electrophoresis and Southern hybridization demonstrated the loss of a 1.1-Mb chromosome in the non-toxin-producing isolate. Since this chromosome can be entirely lost without affecting growth, but is necessary for pathogenicity, we propose it is a conditionally dispensable chromosome.
authors.affiliation: Laboratory of Plant Pathology, Faculty of Agriculture, Tottori University, Japan.
authors.forename: L J
authors.initials: LJ
authors.lastname: Johnson
authors.forename: R D
authors.initials: RD
authors.lastname: Johnson
authors.forename: H
authors.initials: H
authors.lastname: Akamatsu
authors.forename: A
authors.initials: A
authors.lastname: Salamiah
authors.forename: H
authors.initials: H
authors.lastname: Otani
authors.forename: K
authors.initials: K
authors.lastname: Kohmoto
authors.forename: M
authors.initials: M
authors.lastname: Kodama
mesh_terms: D000528:Alternaria / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity; D001483:Base Sequence; D001681:Biological Assay; D015139:Blotting, Southern; D015825:Chromosomes, Fungal / Q000235:genetics*; D004271:DNA, Fungal / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D027845:Malus / Q000382:microbiology; D009183:Mycotoxins / Q000096:biosynthesis / Q000235:genetics; D010453:Peptide Synthases / Q000235:genetics / Q000378:metabolism; D010456:Peptides, Cyclic / Q000096:biosynthesis / Q000235:genetics; D019105:Random Amplified Polymorphic DNA Technique; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014774:Virulence / Q000235:genetics
chemical_list: D004271:DNA, Fungal; D009183:Mycotoxins; D010456:Peptides, Cyclic; C414537:AM-toxin synthetase; D010453:Peptide Synthases