JASMONATE-INDUCIBLE GENES ARE ACTIVATED IN RICE BY PATHOGEN ATTACK WITHOUT A CONCOMITANT INCREASE IN ENDOGENOUS JASMONIC ACID LEVELS

The possible role of the octadecanoid signaling pathway with jasmonic acid (JA) as the central component in defense-gene regulation of patho gen-attacked rice was studied. Rice (Oryza sativa L.) seedlings were t reated with JA or inoculated with the rice blast fungus Magnaporthe gr isea (Hebert) Parr., and gene-expression patterns were compared betwee n the two treatments. IA application induced the accumulation of a num ber of pathogenesis-related (PR) gene products at the mRNA and protein levels, but pathogen attack did not enhance the levels of (-)-JA duri ng the time required for PR gene expression. Pathogen-induced accumula tion of PR1-like proteins was reduced in plants treated with tetcyclac is, a novel inhibitor of jasmonate biosynthesis. There was an additive and negative interaction between JA and an elicitor from M. grisea wi th respect to induction of PR1-like proteins and of an abundant JA- an d wound-induced protein of 26 kD, respectively. Finally, activation of the octadecanoid signaling pathway and induction of a number of PR ge nes by exogenous application of JA did not confer local acquired resis tance to rice. The data suggest that accumulation of nonconjugated (-) -JA is not necessary for induction of PR genes and that JA does not or chestrate localized defense responses in pathogen-attacked rice. Inste ad, IA appears to be embedded in a signaling network with another path ogen-induced pathway(s) and may be required at a certain minimal level for induction of some PR genes.