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First published online June 12, 2003; 10.1104/pp.103.019943 Plant Physiology 132:1623-1630 (2003) © 2003 American Society of Plant Biologists PINOID-Mediated Signaling Involves Calcium-Binding ProteinsInstitute of Biology, Leiden University, Wassenaarseweg b4 2333 AL Leiden, The Netherlands (R.B., C.S.G.A., P.J.J.H., R.O.)
The plant hormone auxin is a central regulator of plant development. In Arabidopsis, the PINOID (PID) protein serine/threonine kinase is a key component in the signaling of this phytohormone. To further investigate the biological function of PID, we performed a screen for PID-interacting proteins using the yeast two-hybrid system. Here, we show that PID interacts with two calcium-binding proteins: TOUCH3 (TCH3), a calmodulin-related protein, and PID-BINDING PROTEIN 1 (PBP1), a previously uncharacterized protein containing putative EF-hand calcium-binding motifs. The interaction between PID and the calcium-binding proteins is significant because it is calcium dependent and requires an intact PID protein. Furthermore, the expression of all three genes (PID, TCH3, and PBP1) is up-regulated by auxin. TCH3 and PBP1 are not targets for phosphorylation by PID, suggesting that these proteins act upstream of PID. PBP1 was found to stimulate the autophosphorylation activity of PID, and calcium influx and calmodulin inhibitors where found to enhance the activity of PID in vivo. Our results indicate that TCH3 and PBP1 interact with the PID protein kinase and regulate the activity of this protein in response to changes in calcium levels. This work provides the first molecular evidence for the involvement of calcium in auxin-regulated plant development.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.103.019943. 1 Present address: Center of Applied Genetics, University of Agricultural Sciences, Muthgasse 18, A1190 Vienna, Austria. * Corresponding author; e-mail offringa{at}rulbim.leidenuniv.nl; fax 31715274999. Received January 6, 2003; returned for revision February 4, 2003; accepted April 4, 2003. This article has been cited by other articles:
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