GENE-EXPRESSION PATTERNS AND LEVELS OF JASMONIC ACID IN RICE TREATED WITH THE RESISTANCE INDUCER 2,6-DICHLOROISONICOTINIC ACID

Acquired disease resistance can be induced in rice (Oryza sativa) by a number of synthetic or natural compounds, but the molecular mechanism s behind the phenomenon are poorly understood. One of the synthetic in ducers of resistance, 2,6-dichloroisonicotinic acid (INA), efficiently protected rice leaves from infection by the rice blast fungus Magnapo rthe grisea (Hebert) Barr. A comparison of gene-expression patterns in plants treated with INA versus plants inoculated with the compatible pathogen M. grisea or the incompatible pathogen Pseudomonas syringae p v syringae revealed only a marginal overlap: 6 gene products, includin g pathogenesis-related proteins (PR1-PR9), accumulated in both INA-tre ated and pathogen-attacked leaves, whereas 26 other gene products accu mulated only in INA-treated or only in pathogen-attacked leaves. Lipox ygenase enzyme activity and levels of nonconjugated jasmonic acid (JA) were enhanced in leaves of plants treated with a high dose of INA (10 0 ppm). Exogenously applied JA enhanced the gene induction and plant p rotection caused by lower doses of INA (0.1 to 10 ppm) that by themsel ves did not give rise to enhanced levels of endogenous (-)-JA. These d ata suggest that INA, aside from activating a pathogen-induced signali ng pathway, also induces events that are not related to pathogenesis. JA acts as an enhancer of both types of INA-induced reactions in rice.