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Beta-Cyanoalanine Synthase as a Molecular Marker for Induced Resistance by Fungal Glycoprotein Elicitor and Commercial Plant Activators

First, second, third, and fourth authors: Department of Life Science, Graduate School of Agricultural Science, Tohoku University, Sendai 981-8555, Japan; fifth author: Department of Plant Pathology, National Agricultural Research Center, Tsukuba 305-8666, Japan; sixth, and seventh authors: Laboratory of Plant Pathology, Faculty of Agriculture, Tokyo University of Agriculture and Technology (TUAT), Tokyo 183-8509, Japan; eighth author: Agricultural & Veterinary Research Labs., Meiji Seika Kaisha, Ltd., Yokohama 222-8567, Japan; ninth author: Chiba Prefectural Agriculture Research Center, Chiba 266-0006, Japan; tenth author: Kazusa DNA Research Institute, Kisarazu 292-0812, Japan; and eleventh author: Department of Upland Agriculture, National Agricultural Research Center for Hokkaido Region, Hokkaido 082-0071, Japan

The biocontrol agent Pythium oligandrum produces glycoprotein elicitor in the cell wall fraction, designated CWP, and induces resistance to a broad range of pathogens. To understand the mechanism of CWP-induced resistance to pathogens, gene expression at the early stage of CWP treatment in tomato roots was analyzed using a cDNA array. At 4 h after CWP treatment, 144 genes were up-regulated and 99 genes were down-regulated. In the 144 up-regulated genes, nine genes exhibited about eightfold increased expression. Analysis of the response of these nine genes to three commercial plant activators indicated that a high level of one gene, beta-cyanoalanine synthase gene (LeCAS) encoding hydrogen cyanide (HCN) detoxification enzyme, was stably induced in tomato roots by such treatment. However, expression of LeCAS was not significantly induced in tomato roots at 4 h by abiotic stresses, whereas only a very low level of induction of such expression by cold stress was observed. This LeCAS expression was also induced after exogenous treatment with a low level of 1-amino-cyclopropane-1-carboxylate as the precursor of ethylene, but not with either salicylic acid or methyl jas-monate. The induction of LeCAS expression in CWP-treated and plant activator-treated roots is likely to be caused by the detoxification of HCN during ethylene production. Transient activation of LeCAS expression caused by ethylene production in tomato roots may be a general phenomenon in fungal elicitor-induced and synthetic plant activator-induced resistance. LeCAS seems to be useful for screening possible novel plant activators for plant protection against pathogens.

Additional keywords: elicitin-like protein, global gene expression.