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First published online August 4, 2006; 10.1104/pp.106.084798 Plant Physiology 142:564-573 (2006) © 2006 American Society of Plant Biologists OPEN ACCESS ARTICLE
Adenosine Kinase Modulates Root Gravitropism and Cap Morphogenesis in Arabidopsis1,[W],[OA]Laboratory of Genetics (L.-S.Y., B.R.H., N.M.U.M., P.H.M.) and Plant Breeding and Plant Genetics Program (L.-S.Y.), University of Wisconsin, Madison, Wisconsin 53706; Department of Biology, University of Waterloo, Ontario, Canada N2L 3G1 (B.A.M.); and Biology Department, Pennsylvania State University, University Park, Pennsylvania 16802 (S.G.)
Adenosine kinase (ADK) is a key enzyme that regulates intra- and extracellular levels of adenosine, thereby modulating methyltransferase reactions, production of polyamines and secondary compounds, and cell signaling in animals. Unfortunately, little is known about ADK's contribution to the regulation of plant growth and development. Here, we show that ADK is a modulator of root cap morphogenesis and gravitropism. Upon gravistimulation, soluble ADK levels and activity increase in the root tip. Mutation in one of two Arabidopsis (Arabidopsis thaliana) ADK genes, ADK1, results in cap morphogenesis defects, along with alterations in root sensitivity to gravistimulation and slower kinetics of root gravitropic curvature. The kinetics defect can be partially rescued by adding spermine to the growth medium, whereas the defects in cap morphogenesis and gravitropic sensitivity cannot. The root morphogenesis and gravitropism defects of adk1-1 are accompanied by altered expression of the PIN3 auxin efflux facilitator in the cap and decreased expression of the auxin-responsive DR5-GUS reporter. Furthermore, PIN3 fails to relocalize to the bottom membrane of statocytes upon gravistimulation. Consequently, adk1-1 roots cannot develop a lateral auxin gradient across the cap, necessary for the curvature response. Interestingly, adk1-1 does not affect gravity-induced cytoplasmic alkalinization of the root statocytes, suggesting either that ADK1 functions between cytoplasmic alkalinization and PIN3 relocalization in a linear pathway or that the pH and PIN3-relocalization responses to gravistimulation belong to distinct branches of the pathway. Our data are consistent with a role for ADK and the S-adenosyl-L-methionine pathway in the control of root gravitropism and cap morphogenesis.
1 This work was supported by the National Science Foundation (to P.H.M. and S.G.), by the National Aeronautics and Space Administration (to P.H.M. and S.G.), by the University of Wisconsin-Madison Graduate School (Hatch funds and a grant-in-aid to P.H.M.), and by the Natural Sciences and Engineering Research Council of Canada (to B.A.M.). This is manuscript number 3630 of the Laboratory of Genetics. 2 Present address: Hung-Yang Bio-Tech, Taichung City, Taiwan. 3 Present address: Department of Biology, Colorado State University, Fort Collins, CO 80523. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Patrick H. Masson (phmasson{at}wisc.edu). [W] The online version of this article contains Web-only data. [OA] Open Access articles can be viewed online without a subscription. www.plantphysiol.org/cgi/doi/10.1104/pp.106.084798 * Corresponding author; e-mail phmasson{at}wisc.edu; fax 608–262–2976. Received June 7, 2006; accepted July 26, 2006; published August 4, 2006. This article has been cited by other articles:
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