Present address: Centre for Endocrinology, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry, London EC1M 6BQ, UK.
The subcellular distribution of the Arabidopsis histidine phosphotransfer proteins is independent of cytokinin signaling
Article first published online: 3 FEB 2010
© 2010 The Authors. Journal compilation © 2010 Blackwell Publishing Ltd
The Plant Journal
Volume 62, Issue 3, pages 473–482, May 2010
How to Cite
Punwani, J. A., Hutchison, C. E., Schaller, G. E. and Kieber, J. J. (2010), The subcellular distribution of the Arabidopsis histidine phosphotransfer proteins is independent of cytokinin signaling. The Plant Journal, 62: 473–482. doi: 10.1111/j.1365-313X.2010.04165.x
- Issue published online: 16 APR 2010
- Article first published online: 3 FEB 2010
- Received 22 October 2009; revised 18 December 2009; accepted 22 January 2010; published online 3 March 2010.
- nuclear–cytosolic movement;
- histidine phosphotransfer
Cytokinins are a class of mitogenic plant hormones that play an important role in most aspects of plant development, including shoot and root growth, vascular and photomorphogenic development and leaf senescence. A model for cytokinin perception and signaling has emerged that is similar to bacterial two-component phosphorelays. In this model, binding of cytokinin to the extracellular domain of the Arabidopsis histidine kinase (AHKs) receptors induces autophosphorylation within the intracellular histidine-kinase domain. The phosphoryl group is subsequently transferred to cytosolic Arabidopsis histidine phosphotransfer proteins (AHPs), which have been suggested to translocate to the nucleus in response to cytokinin treatment, where they then transfer the phosphoryl group to nuclear-localized response regulators (Type-A and Type-B ARRs). We examined the effects of cytokinin on AHP subcellular localization in Arabidopsis and, contrary to expectations, the AHPs maintained a constant nuclear/cytosolic distribution following cytokinin treatment. Furthermore, mutation of the conserved phosphoacceptor histidine residue of the AHP, as well as disruption of multiple cytokinin signaling elements, did not affect the subcellular localization of the AHP proteins. Finally, we present data indicating that AHPs maintain a nuclear/cytosolic distribution by balancing active transport into and out of the nucleus. Our findings suggest that the current models indicating relocalization of AHP protein into the nucleus in response to cytokinin are incorrect. Rather, AHPs actively maintain a consistent nuclear/cytosolic distribution regardless of the status of the cytokinin response pathway.