P. Hassa et al., Syringolin-mediated activation of the Pir7b esterase gene in rice cells issuppressed by phosphatase inhibitors, MOL PL MICR, 13(3), 2000, pp. 342-346
Inoculation of rice plants (Oryza sativa) with the nonhost pathogen Pseudom
onas syringae pv, syringae leads to the activation of defense-related genes
and ultimately to induced resistance against the rice blast fungus Pyricul
aria oryzae, One of the molecular determinants of P. syringae pv, syringae
that is recognized by the plant cells and evokes these defense responses is
syringolin A, an elicitor that is secreted by the bacteria under appropria
te conditions. In order to investigate signal transduction events elicited
by syringolin A, the response of cultured rice cells to syringolin A applic
ation was analyzed. Cultured rice cells were able to sense syringolin A at
concentrations in the nanomolar range as observed by the transient accumula
tion of Pir7b esterase transcripts. Syringolin A-mediated Pir7b transcript
accumulation was inhibited by cyclohexamide, indicating that de novo protei
n synthesis was required. Calyculin and okadaic acid, two protein phosphata
se inhibitors, blocked Pir7b gene induction, whereas the serine/threonine p
rotein kinase inhibitors staurosporine and K-252a had no effect on Pir7b tr
anscript levels. Actin transcript levels were essentially not affected by i
nhibitor treatments over the experimental time span. These results imply th
at dephosphorylation of a phosphoprotein is an important step in the syring
olin A-triggered signal transduction pathway.