Function of calcium‐dependent protein kinase CPK28 of Arabidopsis thaliana in plant stem elongation and vascular development

Abstract

SUMMARYAfter a period of vegetative growth, plants undergo a developmental switch to the reproductive phase, inducing the transition to bolting, elongation of the inflorescence and flowering. We have identified calcium-dependent protein kinase CPK28 from Arabidopsis thaliana as a regulatory component that controls stem elongation and vascular development. In two independent mutant alleles of cpk28, a reduction of stem elongation, accompanied by shorter leaf petioles and enhanced anthocyanin levels, is observed upon the transition to the generative phase. Anatomical analysis revealed an altered vascular pattern characterised by fewer xylem tracheary elements but at the same time increased lignification and secondary growth. Coincident with these morphological changes, cpk28 mutants showed altered expression of NAC transcriptional regulators NST1 and NST3 as well as of GA3ox1, a key regulator of gibberellic acid homeostasis. In vitro protein kinase activity of CPK28 is strictly calcium-dependent. Furthermore, CPK28 is phosphorylated in vivo at several sites. Site-specific amino acid substitutions at these phosphorylation sites resulted in reduced in vitro activity. However, when introduced into a cpk28 mutant background, wild-type and phosphorylation site variants, but not kinase-inactive variants of CPK28 complemented the morphological and developmental defects. Our data identify CPK28 as a developmentally controlled regulator for coordinated stem elongation and secondary growth.

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

“…Furthermore, CPK12 serves as a negative ABA-signaling regulator in seed germination and postgermination growth, which is different from the function of its homologs, CPK4 and CPK11 (Zhao et al, 2011). In addition to abiotic stress, some Arabidopsis CDPKs have been reported to be involved in the plant innate immune response (CPKs 4, 5, 6, and 11 [Boudsocq et al, 2010], CPK1 [Coca and San Segundo, 2010], and CPK5 [Dubiella et al, 2013]), herbivoryinduced signaling network (CPK3 and CPK13; Kanchiswamy et al, 2010), regulation of pollen tube growth (CPK17 and CPK34 [Myers et al, 2009], CPK11 and CPK24 , CPK2 and CPK20 [Gutermuth et al, 2013], and CPK32 [Zhou et al, 2014]), and stem elongation and vascular development (CPK28; Matschi et al, 2013).…”

Reduced Biosynthesis of Digalactosyldiacylglycerol, a Major Chloroplast Membrane Lipid, Leads to Oxylipin Overproduction and Phloem Cap Lignification in Arabidopsis

“…Since ectopic lignification in phloem cap cells has been observed in other mutants, including deetiolated3 (det3, encoding V-ATPase subunit C; Newman et al, 2004), ectopic lignification1 (eli1, encoding cellulose synthase CESA3; Caño-Delgado et al, 2003), broomhead (encoding eukaryotic release factor eRF1; Petsch et al, 2005), cpk28 (encoding a calcium-dependent protein kinase; Matschi et al, 2013), ectopic deposition of lignin in pith1 (elp1, encoding a chitinase; Zhong et al, 2000), and wrky12 (encoding a WRKY transcription factor; Wang et al, 2010), we analyzed the expression of these genes in the dgd1-1 mutant and found no reduction in expression of any of these genes compared with the wild type (Supplemental Figure 2). …”

Plant Purine Nucleoside Catabolism Employs a Guanosine Deaminase Required for the Generation of Xanthosine in Arabidopsis

“…The product was inserted into pI2-pCPK28-GUS-mcs2 (Matschi et al, 2013), releasing the promoter of CPK28 (pCPK28) and generating the construct pI2-pGSDA-GUS-mcs2.…”

“…Acquired images were processed using the Leica Microsystems Leica Application Suite Advanced Fluorescence software and Adobe Photoshop CS6. Staining for GUS activity was performed according to Matschi et al (2013).…”