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First published online December 7, 2007; 10.1104/pp.107.109587 Plant Physiology 146:762-771 (2008) © 2008 American Society of Plant Biologists OPEN ACCESS ARTICLE
Altered Profile of Secondary Metabolites in the Root Exudates of Arabidopsis ATP-Binding Cassette Transporter Mutants1,[C],[W],[OA]Center for Rhizosphere Biology (D.V.B., V.M.L.-V., C.D.B., C.D.-l.-P., J.M.V.), and Department of Chemistry (F.S.), Colorado State University, Fort Collins, Colorado 80523; Unidad de Bioquimica y Biologia Molecular de Plantas, Centro de Investigacion Cientifica de Yucatan, Col. Chuburna de Hidalgo, 97000 Merida, Yucatan, Mexico (V.M.L.-V.); Zurich-Basel Plant Science Center, Institute of Plant Biology, Molecular Plant Physiology, University of Zurich, CH–8008 Zurich, Switzerland (M.J., D.S., E.M.); Institute of Bioorganic Chemistry, Polish Academy of Sciences, 61–704, Poznan, Poland (M.J.); Samuel Roberts Noble Foundation, Plant Biology Division, Ardmore, Oklahoma 73401 (L.W.S.); and Department of Biology, Williams College, Williamstown, Massachusetts 01267 (L.M.B.)
Following recent indirect evidence suggesting a role for ATP-binding cassette (ABC) transporters in root exudation of phytochemicals, we identified 25 ABC transporter genes highly expressed in the root cells most likely to be involved in secretion processes. Of these 25 genes, we also selected six full-length ABC transporters and a half-size transporter for in-depth molecular and biochemical analyses. We compared the exuded root phytochemical profiles of these seven ABC transporter mutants to those of the wild type. There were three nonpolar phytochemicals missing in various ABC transporter mutants compared to the wild type when the samples were analyzed by high-performance liquid chromatography-mass spectrometry. These data suggest that more than one ABC transporter can be involved in the secretion of a given phytochemical and that a transporter can be involved in the secretion of more than one secondary metabolite. The primary and secondary metabolites present in the root exudates of the mutants were also analyzed by gas chromatography-mass spectrometry, which allowed for the identification of groups of compounds differentially found in some of the mutants compared to the wild type. For instance, the mutant Atpdr6 secreted a lower level of organic acids and Atmrp2 secreted a higher level of amino acids as compared to the wild type. We conclude that the release of phytochemicals by roots is partially controlled by ABC transporters.
1 This work was supported by the National Science Foundation (grant nos. MCB–0542642 to J.M.V. and F.R.S. and MCB0416471 to L.M.B.), and by the Swiss National Foundation within the National Centres of Competence in Research "Plant Survival" and the European Union Project Plant Transporters (grant no. HPRN–CT–2002–00269 to E.M.). 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: J.M. Vivanco (j.vivanco{at}colostate.edu). [C] Some figures in this article are displayed in color online but in black and white in the print edition. [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.107.109587 * Corresponding author; e-mail j.vivanco{at}colostate.edu. Received September 23, 2007; accepted November 27, 2007; published December 7, 2007. Related articles in Plant Physiol.:
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