U. S. -Japan joint research on the molecular pathology of host-specific-toxin-depending fungal infection to plants

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l. Occurrence of AM-toxin an ACT-toxin producing Alternaria Alternata in North America : The pathogen for new alternariosis on Delicious lines in North Carolina apple orchards was found to produce AM-toxin I by bioassay and HPLC analysis, and to fall into the apple pathotype of Alternaria alternate.2. Biochemical analysis revealed that although AK-, ACT-, AM-, ACR- and HMT-toxins have different primary targets in susceptibility genotypes, they exert in common an ability to induce host-specifically the accessibility to invader by nullifying dynamic defense mechanisms in plant cells.3. Pyricularia oryzae causing rice blast produced an infection-inducing factor on germination, which may involve in establishment of the basic compatability between rice plants and the fungus.4. Detection and isolation of toxin receptors : (1) Covalent binding sites of victorin (HV-toxin) in oat leaf tissues were detected by polyclonal, antibodies : in vivo binding of victorin to proteins of 100 and 45 Kd was … More observed in both susceptible and resistanit cultivars of oats, and also, in vitro binding to 100, 55 and 45 Kd in both genotypes. (2) AK-toxin was found to bind to plasma membranes purified from susceptible cultivar, but not those from resistant, of Japanese pear. To confirm, polyclonal anti-AK-toxin antibodies are raising in rabbits.5. Cochliobolus carbonum race 1 possesses two multifunctional enzymes required for HC-toxin cyclic peptide synthesis, HTS-1 & HTS-2, which activate-certain member amino acids by ATP/PPI exchange. A partial CDNA clone, encoding HTS-1 (220 kd) was identified using a specific polyclonal anti-HTS-1 antibody and by hybridization, to a synthetic oligonucleotide corresponding to the amino acid sequence of a tryptic peptide of the enzyme. The gene for HTS-1 is part of a contiguous 22 kb of DNA that is present in isolates of the fungus that make HC-toxin and is lacking in those that do not.6. An efficient integrative transformation system (PDH25rla) for Alternaria alternata was established by using a plasmid vector PDH25 and a highly repetitive ribosomalRNA gene cluster (rDNA) of A. alternata. The transformation occurred by homologous recombination as a single crossover between the plasmid-borne RDNA segment and its homologue in the chromosome.7. HC-toxin reductase that inactivates HC-toxin at the essential carbonyl group, is detectable only in extracts of maize that are resistant to C. carbonium race 1 (genotype Hm/Hm or Hm/hm). Less