植物免疫プライミング剤の単離と作用機序解明

　Plant disease resistance inducers, so-called plant activators, are agrochemicals that protect crops from pathogens. They confer long-lasting resistance against a broad range of diseases by activating their immune system. Since plant activators impinge on host plants, unlike commonly-used pesticides which directly target pathogens, no drug-resistant microbes for plant activators have been found so far in the field. They originated from probenazole (Oryzemate ) and have been widely used over 30 years for the protection of paddy-field rice from blast fungus and bacterial leaf blight in East Asia. In spite of the advantages of plant activators, their application is still limited. The lack of both knowledge about their modes of action and an appropriate high-throughput screening system restrict the isolation of novel compounds. We established a highthroughput chemical screening procedure to identify plant immune-priming compounds which increase but do not directly induce immune responses in Arabidopsis suspension cells upon infection of the bacterial pathogen, Pseudomonas syringae pv. tomato DC3000 avrRpm1. From the screening of a commercially available chemical library of 10,000 diverse small organic molecules, we identified seven compounds that prime the immune response and we designated them ‘imprimatins’ for immune-priming chemicals. The isolated compound, imprimatin C1 activates the expression of defense-related genes independent of pathogen and functions as a weak analog of salicylic acid (SA). Those originally-isolated three compounds and their four derivatives were classified into two groups with distinct molecular structures and they weve named imprimatins A and B. We found that they conferred disease resistance in plants by inhibiting both a known and a previously unknown SA glucosyltransferase (SAGT). Imprimatins and their targets are useful for the development of practical plant activators and also their modes of action might give a clue for novel crop protection technology.

研究紹介 (Research Report)