U.S.-Japan Joint Research on Molecular Biology of Host-specific Toxins as Pathogenicity

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1.Non-ribozomal, multi-function enzyme systems involved in biosynthesis of AM-and HC-toxins by each pathogen. TOX2 locus in H.carbonum has HTS1 gene (22 kb) encoding 570 kD protein which have 4 domains : Domain B had L-proline-activation and isomerization when expressed in recombinant baculovirus/insect cell culture.2.Function and chromosomal location of the Cochliobolus heterostrophus TOX1 locus were investigated by tagging by insertional mutagenesis & REMI procedure. Two essential TOX1 loci that encode a polyketide synthase are on different chromosomes of race T strains. They could not be resolved without molecular technology because in conventional genetic crosses between race T and race O they are linked to the break point of a reciprocal translocation.3.Attempts to clone a gene for AK-toxin biosynthesis in Alternaria alternata Japanese pear pathotype was made by using insertional mutagenesis. The sequences flanking the transfoming DNA were isolated from genomic DNA of a Tox^- transformant by means of plasmid rescue. Wild-type genomic sequences were cloned by screening a genomic DNA library of the wild-type strain with the sequences flanking the transforming DNA of the rescued plasmid. The selected genomic clones have been characterizing.4.A disease resistance gene Hm1 was found to code the enzyme which detoxify HC-toxin released from Chocliobolus carbonum race 1, cause of leaf spot of maize.5.Pathological roles of fungal melanin, beta-1,3-glucanase and cutinase were examined by technology of molecular genetics.6.Part of the results obtained in the project was published as a Proceedings of Tottori University International Symposium on Host-Specific toxin (1994).