| Co-Investigator(Kenkyū-buntansha) |
KOBAYASHI Hirokazu SHIZUOKA PREFEC.UNIV., FAC.OF FOOD AND NUTRITION SCIENCE, ASSIST.PROF., 食品栄養科学部, 助教授 (80170348)
TSUGE Takshi NAGOYA UNIV., FAC. OF AGRIC., ASSIST.PROF., 農学部, 助教授 (30192644)
NAKATSUKA Shinichi GIFU UNIV., FAC. OF AGRIC., ASSIST.PROF., 農学部, 助教授 (30109318)
ARASE Sakae SHIMANE UNIV., FAC. OF AGRIC., ASSIST.PROF., 農学部, 助教授 (40127478)
OTANI Hiroshi TOTTORI UNIV., FAC. OF AGRIC., PROFESSOR, 農学部, 教授 (50032305)
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| Research Abstract |
An interdisiplinary project for 3 years was conducted to elucidate the molecular basis of plant infection by toxigenic fungal pathogens with host-specific toxins (HST). A proposed scheme for disease establishment that an HST released during spore germination binds a putative toxin-binding site (receptor) in potential host plant, where the HST-signal induces the state of accessibility to the invader, and then the producing fungus is eventually able to colonize the plant, was developed as follows:
1) ACT-, BZR-, AT- and Pyricularia oryzae-toxins were isolated from germination fluids of the pathogens, and structures of the former two toxins were elucidated. ACT-toxin shared in structure a decatrtienoic acid with AK- and AF-toxins, while BZR-toxin composed of homologs of cyclic depsipeptides that were bioactive only when they co-exisited at least two members (co-toxin). On the other hand, a structure-activity corelation study revealed that there is coincidence between the host ranges of the
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Japanese pear, strawberry and tangerine pathotypes of Alternaria alternata and the plant ranges sensitive to AK-, AF- and ACT-toxins they produced, suggesting that host-specificity of the fungus is precisely determined at the molecular level.
2) Biosynthetic pathways of AK-, AF- and ACT-toxins were proposed, depending on structural analysis of intermediate metabolites and tracer experiments. Enzymatic basis for AM-toxin synthesis also examined.
3) Cascade-like signal transduction processes of HSTs actions were dissected by means of physiological, biochemical and ultrastructural approaches.
4) A highly efficient integrative transformation system was estalished for Alternaria alternata: the vector pDH25rla was constructed by inserting a highly repetitive ribosomal RNA gene cluster (rDNA) sequence into a unique Xbal site of pDH25. Using this, 3 genes for fungal melanin biosynthesis (ALM, BRM1, BRM2) were isolated as a model for cloning pathogenicity genes.
5) For HST-receptor studies, anti-HST anibodies were generated. A possible receptor protein was detected in the plasma membrane fraction of susceptible pear calli but not of resistant cell line derived from the same susceptible calli. Less
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