Jasmonate-Inducible Genes Are Activated in Rice by Pathogen Attack without a Concomitant Increase in Endogenous Jasmonic Acid Levels

Abstract

Jersey 08903-0231 (P. Silverman, M.S., I.R.)The possible role of the octadecanoid signaling pathway with jasmonic acid (JA) as the central component i n defense-gene regulation of pathogen-attacked rice was studied. Rice (Oryza sativa 1.) seedlings were treated with JA or inoculated with the rice blast fungus Magnaporthe grisea (Hebert) Barr., and gene-expression patterns were compared between the two treatments. JA application induced the accumulation of a number of pathogenesis-related (PR) gene products at the mRNA and protein levels, but pathogen attack did not enhance the levels of (-)-JA during the time required for PR gene expression. Pathogen-induced accumulation of PR1 -like proteins was reduced in plants treated with tetcyclacis, a nove1 inhibitor of jasmonate biosynthesis. There was an additive and negative interaction between JA and an elicitor from M. grisea with respect to induction of PR1-like proteins and of an abundant JA-and wound-induced protein of 26 kD, respectively. Finally, activation of the octadecanoid signaling pathway and induction of a number of PR genes by exogenous application of JA did not confer local acquired resistance t o rice. The data suggest that accumulation of nonconjugated (-)-JA is not necessary for induction of PR genes and that JA does not orchestrate localized defense responses in pathogen-attacked rice. Instead, JA appears to be embedded in a signaling network with another pathogen-induced pathway(s) and may be required at a certain minimal leve1 for induction of some PR genes.The plant-growth regulator JA, first described as the methyl ester MeJA in the essential oils of Jasminum (Demole et al., 1962), has been attributed to a number of regulating functions in plant development (for review, see Sembdner and Parthier 119931). Only recently has attention been paid to jasmonates as the key molecules of the octadecanoid signaling pathway mediating the activation of defense responses in herbivore-or pathogen-attacked plants (for review, see Sembdner and Parthier [1993], Farmer [1994], and Creelman and Mullet [1995]). The wound and pathogen

Differential Expression of a Novel Gene in Response to Coronatine, Methyl Jasmonate, and Wounding in the Coi1Mutant of Arabidopsis1

“…This apparent paradox remains to be clarified, since MeJA is suggested to play a role in plant-defense responses (Coehn et al, 1993;Mueller et al, 1993;Reinbothe et al, 1994). Nevertheless, no correlation could be found between jasmonates and defense responses in plant-pathogen interactions (Schweizer et al, 1993;Kogel et al, 1995;Schweizer et al, 1997). How coronatine could function as a virulence factor by mimicking MeJA in a bacteria-plant interaction is an open question.…”

A Wheat Xylanase Inhibitor Gene,Xip-I, but NotTaxi-I, Is Significantly Induced by Biotic and Abiotic Signals That Trigger Plant Defense

“…9,10) Wounding causes a strong and transient accumulation of JA, followed by the induction of a number of pathogenesis-related (PR) genes, in the treated leaf. 11) Thus the expression profiles of Xip-I obtained in this study, viz., wound-, MeJA-, and pathogen-inducibility, indicate that Xip-I is a PR gene involved in plant defense.…”

Rhizobacteria-mediated induced systemic resistance (ISR) in Arabidopsis requires sensitivity to jasmonate and ethylene but is not accompanied by an increase in their production

“…In other plant systems similar phenomena have been reported. For instance, Schweizer et al [41] demonstrated that during infection of rice with the fungal pathogen Magnaporthe grisea, jasmonate-inducible genes are activated without an increase in endogenous JA levels. Moreover, Tsai et al [47] provided evidence that an increase in ethylene sensitivity rather than ethylene production is the initial event in triggering JA-enhanced senescence in detached rice leaves.…”