title: Calcium-dependent protein kinases regulate polarized tip growth in pollen tubes.
abstract: Calcium signals are critical for the regulation of polarized growth in many eukaryotic cells, including pollen tubes and neurons. In plants, the regulatory pathways that code and decode Ca(2+) signals are poorly understood. In Arabidopsis thaliana, genetic evidence presented here indicates that pollen tube tip growth involves the redundant activity of two Ca(2+)-dependent protein kinases (CPKs), isoforms CPK17 and -34. Both isoforms appear to target to the plasma membrane, as shown by imaging of CPK17-yellow fluorescent protein (YFP) and CPK34-YFP in growing pollen tubes. Segregation analyses from two independent sets of T-DNA insertion mutants indicate that a double disruption of CPK17 and -34 results in an approximately 350-fold reduction in pollen transmission efficiency. The near sterile phenotype of homozygous double mutants could be rescued through pollen expression of a CPK34-YFP fusion. In contrast, a transgene rescue was blocked by mutations engineered to disrupt the Ca(2+)-activation mechanism of CPK34 (CPK34-YFP-E465A,E500A), providing in vivo evidence linking Ca(2+) activation to a biological function of a CPK. While double mutant pollen tubes displayed normal morphology, relative growth rates for the most rapidly growing tubes were reduced by more than three-fold compared with wild type. In addition, while most mutant tubes appeared to grow far enough to reach ovules, the vast majority (>90%) still failed to locate and fertilize ovules. Together, these results provide genetic evidence that CPKs are essential to pollen fitness, and support a mechanistic model in which CPK17 and -34 transduce Ca(2+) signals to increase the rate of pollen tube tip growth and facilitate a response to tropism cues.
authors.affiliation: Biochemistry Department MS200, University of Nevada, Reno, NV 89557, USA.
authors.forename: Candace
authors.initials: C
authors.lastname: Myers
authors.forename: Shawn M
authors.initials: SM
authors.lastname: Romanowsky
authors.forename: Yoshimi D
authors.initials: YD
authors.lastname: Barron
authors.forename: Shilpi
authors.initials: S
authors.lastname: Garg
authors.forename: Corinn L
authors.initials: CL
authors.lastname: Azuse
authors.forename: Amy
authors.initials: A
authors.lastname: Curran
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Davis
authors.forename: Jasmine
authors.initials: J
authors.lastname: Hatton
authors.forename: Alice C
authors.initials: AC
authors.lastname: Harmon
authors.forename: Jeffrey F
authors.initials: JF
authors.lastname: Harper
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D004269:DNA, Bacterial; D018744:DNA, Plant / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D051479:Plant Infertility; D053205:Pollen Tube / Q000201:enzymology / Q000254:growth & development*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D017871:Calcium-Calmodulin-Dependent Protein Kinases
chemical_list: D029681:Arabidopsis Proteins; D002118:Calcium; D004269:DNA, Bacterial; D018744:DNA, Plant; D020033:Protein Isoforms; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C036483:T-DNA