The Ca2+-dependent protein kinase CPK3 is required for MAPK-independent salt-stress acclimation in Arabidopsis

Abstract

Plants use different signalling pathways to respond to external stimuli. Intracellular signalling via calcium-dependent protein kinases (CDPKs) or mitogen-activated protein kinases (MAPKs) present two major pathways that are widely used to react to a changing environment. Both CDPK and MAPK pathways are known to be involved in the signalling of abiotic and biotic stresses in animal, yeast and plant cells. Here, we show the essential function of the CDPK CPK3 (At4g23650) for salt stress acclimation in Arabidopsis thaliana, and test crosstalk between CPK3 and the major salt-stress activated MAPKs MPK4 and MPK6 in the salt stress response. CPK3 kinase activity was induced by salt and other stresses after transient overexpression in Arabidopsis protoplasts, but endogenous CPK3 appeared to be constitutively active in roots and leaves in a strictly Ca2+-dependent manner. cpk3 mutants show a salt-sensitive phenotype comparable with mutants in MAPK pathways. In contrast to animal cells, where crosstalk between Ca2+ and MAPK signalling is well established, CPK3 seems to act independently of those pathways. Salt-induced transcriptional induction of known salt stress-regulated and MAPK-dependent marker genes was not altered, whereas post-translational protein phosphorylation patterns from roots of wild type and cpk3 plants revealed clear differences. A significant portion of CPK3 was found to be associated with the plasma membrane and the vacuole, both depending on its N-terminal myristoylation. An initial proteomic study led to the identification of 28 potential CPK3 targets, predominantly membrane-associated proteins.

Arabidopsis CALCIUM-DEPENDENT PROTEIN KINASE8 and CATALASE3 Function in Abscisic Acid-Mediated Signaling and H2O2 Homeostasis in Stomatal Guard Cells under Drought Stress

“…Arabidopsis CPK32 has been characterized as an ABA signaling component that regulates ABA-responsive gene expression via ABF4 (Choi et al, 2005). Arabidopsis CPK3 and CPK6 function as positive transducers in plant ion channel regulation and stomatal ABA signaling (Mori et al, 2006), as well as salt and/or drought stress(es) (Mehlmer et al, 2010;Xu et al, 2010). Arabidopsis CPK4 and CPK11 have been identified as important positive regulators in CDPK/calcium-mediated ABA signaling .…”

Molecular Characterization ofHbCDPK1, an Ethephon-Induced Calcium-Dependent Protein Kinase Gene ofHevea brasiliensis

“…25,40) Presently, a CDPK/CPK3 required for MAPK-independent salt-stress acclimation in Arabidopsis has also been demonstrated. 41) Nevertheless, whether and how HbCDPK1 mediates multiple signal transduction pathways and maintains the specificity of its substrate remains to be elucidated. …”

Reactive Oxygen in Abiotic Stress Perception - From Genes to Proteins

“…Other Ca 2+ signalling proteins seem to be involved in the acclimation to abiotic stresses as well. The Ca 2+ -DEPENDENT PROTEIN KINASE 3 (CPK3) provides a parallel pathway to MITOGEN-ACTIVATED PROTEIN KINASE (MAPK) signalling in Arabidopsis thaliana (Mehlmer et al, 2010;Wurzinger et al, 2011). In these cases, just as in the example of SOS1, the importance of Ca 2+ signalling is recognized, but the components that induce Ca 2+ signalling in response to the initial stress remain unknown.…”

“…Protein kinases are important components of the signal transduction cascade that links abiotic stress perception to signal integration and transcriptional reprogramming of the cell (de la Fuente van Bentem et al, 2008;Nakagami et al, 2010;Sugiyama et al, 2008). MAPKs and phosphatases alongside with CPKs are prominent participants in the abiotic stress signalling network (Ichimura et al, 2000;Jonak et al, 2004;Mehlmer et al, 2010;Miller et al, 2008;Mizoguchi et al, 1997;Takahashi et al, 2011;Wurzinger et al, 2011;Yuasa et al, 2001).…”