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 calmodulin in plant defense responses has been developed. We have used a dominant-acting calmodulin mutant (VU-3, Lys to Arg115) to investigate the oxidative burst and nicotinamide co-enzyme fluxes after various stimuli (cellulase, harpin, incompatible bacteria, osmotic and mechanical) that elicit plant defense responses in transgenic tobacco cell cultures. VU-3 calmodulin differs from endogenous plant calmodulin in that it cannot be methylated post-translationally, and as a result it hyperactivates calmodulin-dependent NAD kinase. Cells expressing VU-3 calmodulin 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 coincided both in timing and magnitude with development of the active oxygen species (AOS) burst. These data show that calmodulin is a target of calcium fluxes in response to elicitor or environmental stress, and provide the first evidence that plant NAD kinase may be a downstream target which potentiates AOS production by altering NAD(H)/NADP(H) homeostasis.
Harding
S A
SA
Department of Biochemistry, Cellular and Molecular Biology and Center for Legume Research, University of Tennessee, Knoxville 37996, USA.
Oh
S H
SH
Roberts
D M
DM
D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000235:genetics*; D004789:Enzyme Activation; D015870:Gene Expression; D009249:NADP / Q000378:metabolism; D009536:Niacinamide / Q000378:metabolism; D010101:Oxygen Consumption; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D010812:Physical Stimulation; D030821:Plants, Genetically Modified; D010947:Plants, Toxic; D017354:Point Mutation; D017382:Reactive Oxygen Species / Q000378:metabolism*; D016897:Respiratory Burst; D014026:Nicotiana / Q000235:genetics* / Q000378:metabolism*
D002147:Calmodulin; D017382:Reactive Oxygen Species; D009536:Niacinamide; D009249:NADP; D017853:Phosphotransferases (Alcohol Group Acceptor); C021844:NAD kinase; D002118:Calcium