Characterization of RCI-1, a chloroplastic rice lipoxygenase whose synthesis is induced by chemical plant resistance activators

A full-length lipoxygenase cDNA (RCI-1) has been cloned from rice (Oryza sa tiva) whose corresponding transcripts accumulate in response to treatment o f the plants with chemical inducers of acquired resistance such as benzo(1, 2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH), 2,6-dichloroisonic otinic acid (INA), and probenazol. In contrast, RCI-1 transcript levels did not increase after inoculation with compatible and incompatible races of t he rice blast fungus Magnaporthe grisea and the nonhost pathogen Pseudomona s syringae pv. syringae. RCI-1 transcript levels also increased after exoge nous application of jasmonic acid, but not upon wounding. Dose-response and time course experiments revealed a similar pattern of transcript accumulat ion and lipoxygenase activity in BTH-treated rice leaves. Enzymatic analysi s of recombinant RCI-1 protein produced in Escherichia coli revealed that 1 3-hydroperoxy-octadecanoic acids were the predominant reaction products whe n either linoleic or linolenic acid used as a substrate. The RCI-1 sequence features a putative chloroplast targeting sequence at its N-terminus. Inde ed, a protein consisting of the putative chloroplast transit peptide fused to green fluorescent protein was exclusively localized in chloroplasts, ind icating that RCI-1 is a chloroplastic enzyme.