Studies on accumulation control and physiological functions of jasmonates

Abstract

Jasmonate （JA） regulates many physiological processes of plant stress responses as well as plant development.　We have studied physiological roles of JA in rice defense responses.　The cpm2 and hebiba are rice mutants defective in a gene encoding allene oxide cyclase, a key enzyme of JA biosynthesis.　As endogenous levels of JA were extremely low in both mutants, we treated the mutants with Pyricularia oryzae to investigate the function of JA in defense responses.　The inoculation assays revealed that JA is required for defense against P. oryzae.　We also demonstrated that JA mediates stress-induced accumulation of a flavonoid phytoalexin, sakuranetin.　Additionally, we identified rice naringenin 7-O-methyltransferase （OsNOMT） as a key enzyme of sakuranetin biosynthesis and demonstrated that the expression of OsNOMT was induced by JA.　Studies using osjar1 mutant defective in jasmonoyl-isoleucine （JA-Ile） biosynthesis suggested that JA-Ile is a major signaling molecule in the JA-mediated defense responses.　Additionally, we found that JA response was induced in narrow region around stressed area by using JA-inducible reporter system, suggesting that endogenous JA level is regulated very locally.　Here we summaries our studies focusing on physiological roles of JA in rice defense responses.