Both authors contributed equally.
Calcium-dependent protein kinases regulate polarized tip growth in pollen tubes
Article first published online: 18 MAY 2009
© 2009 The Authors. Journal compilation © 2009 Blackwell Publishing Ltd
The Plant Journal
Volume 59, Issue 4, pages 528–539, August 2009
How to Cite
Myers, C., Romanowsky, S. M., Barron, Y. D., Garg, S., Azuse, C. L., Curran, A., Davis, R. M., Hatton, J., Harmon, A. C. and Harper, J. F. (2009), Calcium-dependent protein kinases regulate polarized tip growth in pollen tubes. The Plant Journal, 59: 528–539. doi: 10.1111/j.1365-313X.2009.03894.x
- Issue published online: 11 AUG 2009
- Article first published online: 18 MAY 2009
- Received 17 October 2008; revised 6 January 2009; accepted 23 March 2009. published online 18 May 2009.
- male sterile;
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 Ca2+ signals are poorly understood. In Arabidopsis thaliana, genetic evidence presented here indicates that pollen tube tip growth involves the redundant activity of two Ca2+-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 Ca2+-activation mechanism of CPK34 (CPK34–YFP–E465A,E500A), providing in vivo evidence linking Ca2+ 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 Ca2+ signals to increase the rate of pollen tube tip growth and facilitate a response to tropism cues.