TRANSGENIC TOBACCO EXPRESSING A FOREIGN CALMODULIN GENE SHOWS AN ENHANCED PRODUCTION OF ACTIVE OXYGEN SPECIES

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.