P. Schweizer et al., JASMONATE-INDUCIBLE GENES ARE ACTIVATED IN RICE BY PATHOGEN ATTACK WITHOUT A CONCOMITANT INCREASE IN ENDOGENOUS JASMONIC ACID LEVELS, Plant physiology, 114(1), 1997, pp. 79-88
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.