Ca2+, cAMP, and transduction of non-self perception during plant immune responses.
Ca(2+) influx is an early signal initiating cytosolic immune responses to pathogen perception in plant cells; molecular components linking pathogen recognition to Ca(2+) influx are not delineated. Work presented here provides insights into this biological system of non-self recognition and response activation. We have recently identified a cyclic nucleotide-activated ion channel as facilitating the Ca(2+) flux that initiates immune signaling in the plant cell cytosol. Work in this report shows that elevation of cAMP is a key player in this signaling cascade. We show that cytosolic Ca(2+) elevation, nitric oxide (NO) and reactive oxygen species generation, as well as immune signaling, lead to a hypersensitive response upon application of pathogens and/or conserved molecules that are components of microbes and are all dependent on cAMP generation. Exogenous cAMP leads to Ca(2+) channel-dependent cytosolic Ca(2+) elevation, NO generation, and defense response gene expression in the absence of the non-self pathogen signal. Inoculation of leaves with a bacterial pathogen leads to cAMP elevation coordinated with Ca(2+) rise. cAMP acts as a secondary messenger in plants; however, no specific protein has been heretofore identified as activated by cAMP in a manner associated with a signaling cascade in plants, as we report here. Our linkage of cAMP elevation in pathogen-inoculated plant leaves to Ca(2+) channels and immune signaling downstream from cytosolic Ca(2+) elevation provides a model for how non-self detection can be transduced to initiate the cascade of events in the cell cytosol that orchestrate pathogen defense responses.
Ma
Wei
W
Agricultural Biotechnology Laboratory, Department of Plant Science, University of Connecticut, 1390 Storrs Road, Storrs, CT 06269-4163, USA.
Qi
Zhi
Z
Smigel
Andries
A
Walker
Robin K
RK
Verma
Rajeev
R
Berkowitz
Gerald A
GA
D000262:Adenylyl Cyclases / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects / Q000276:immunology* / Q000382:microbiology; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects / Q000276:immunology / Q000382:microbiology; D044224:Pseudomonas syringae / Q000187:drug effects / Q000276:immunology; D051192:Receptors, Pattern Recognition / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology*
D004791:Enzyme Inhibitors; D008070:Lipopolysaccharides; D051192:Receptors, Pattern Recognition; D009569:Nitric Oxide; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D002118:Calcium