Calcium-dependent protein kinases regulate polarized tip growth in pollen tubes.
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.
Myers
Candace
C
Biochemistry Department MS200, University of Nevada, Reno, NV 89557, USA.
Romanowsky
Shawn M
SM
Barron
Yoshimi D
YD
Garg
Shilpi
S
Azuse
Corinn L
CL
Curran
Amy
A
Davis
Ryan M
RM
Hatton
Jasmine
J
Harmon
Alice C
AC
Harper
Jeffrey F
JF
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
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