Primary Metabolism in Plant Defense (Regulation of a Bean Malic Enzyme Gene Promoter in Transgenic Tobacco by Developmental and Environmental Cues).

NADP-dependent malic enzyme (NADP-ME, EC 1.1.1.40) catalyzes the oxidative decarboxylation of malate to pyruvate, producing CO2 and NADPH. We have examined regulatory properties of a 2.8-kb promoter-leader fragment of a bean (Phaseolus vulgaris L.) NADP-ME gene (PvME1) predicted to encode a cytosolic form of the enzyme by expression analysis of promoter-[beta]-glucuronidase fusions in transgenic tobacco plants. The PvME1 promoter directed strong expression in stems, which was confined to vascular and pith tissues, and was also active in floral and reproductive tissues. Wounding caused a marked induction of promoter activity, which was further strongly enhanced upon application of stimuli related to pathogen defense. Glutathione (reduced form) was the strongest inducer, but oxidized glutathione, fungal elicitor, cellulase, catalase, ascorbic acid, and NADPH were additional potent promoter-stimulating agents. Responsiveness to reduced glutathione was also shown at the level of PvME1 mRNA accumulation in bean plants. The putative contributions of NADP-ME gene expression to the plant defense response and possible mechanisms of defense gene regulation by conditions of oxidative stress as well as by H2O2 and antioxidant levels are discussed.