Sa. Harding et al., TRANSGENIC TOBACCO EXPRESSING A FOREIGN CALMODULIN GENE SHOWS AN ENHANCED PRODUCTION OF ACTIVE OXYGEN SPECIES, EMBO journal, 16(6), 1997, pp. 1137-1144
A strategy for elucidating specific molecular targets of calcium and c
almodulin in plant defense responses has been developed, We have used
a dominant-acting calmodulin mutant (VU-3, Lys to Arg115) to investiga
te the oxidative burst and nicotinamide co-enzyme fluxes after various
stimuli (cellulase, harpin, incompatible bacteria, osmotic and mechan
ical) that elicit plant defense responses in transgenic tobacco cell c
ultures, VU-3 calmodulin differs from endogenous plant calmodulin in t
hat it cannot be methylated post-translationally, and as a result it h
yperactivates calmodulin-dependent NAD kinase, Cells expressing VU-3 c
almodulin exhibited a stronger active oxygen burst that occurred more
rapidly than in normal control cells challenged with the same stimuli,
Increases in NADPH level were also greater in VU-3 cells and coincide
d both in timing and magnitude with development of the active oxygen s
pecies (AOS) burst, These data show that calmodulin is a target of cal
cium fluxes in response to elicitor or environmental stress, and provi
de the first evidence that plant NAD kinase may be a downstream target
which potentiates AOS production by altering NAD(H)/NADP(H) homeostas
is.