JXB Advance Access originally published online on November 13, 2007
Journal of Experimental Botany 2007 58(14):3905-3914; doi:10.1093/jxb/erm243
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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RESEARCH PAPER |
Phosphatidic acid binds to and inhibits the activity of Arabidopsis CTR1


1Section of Plant Physiology, Swammerdam Institute for Life Sciences, University of Amsterdam, Kruislaan 318, NL-1098 SM Amsterdam, The Netherlands
2Department of Biochemistry, University of California-Riverside, Riverside, California, CA 92521, USA
* To whom correspondence should be addressed. E-mail: testerink{at}science.uva.nl
Phosphatidic acid (PA) has only recently been identified as an important eukaryotic lipid-signalling molecule. In plants, PA formation is triggered by various biotic and abiotic stresses, including wounding, pathogen attack, drought, salinity, cold, and freezing. However, few molecular targets of PA have been identified so far. One of the best characterized is Raf-1, a mammalian MAPKKK. Arabidopsis thaliana CTR1 (constitutive triple response 1) is one of the plant homologues of Raf-1 and functions as a negative regulator of the ethylene signalling pathway. Here, it is shown that PA binds CTR1 and inhibits its kinase activity. Using different PA-binding assays, the kinase domain of CTR1 (CTR1-K) was found to bind PA directly. Addition of PA resulted in almost complete inhibition of CTR1 kinase activity and disrupted the intramolecular interaction between CTR1-K and the CTR1 N-terminal regulatory domain. Additionally, PA blocked the interaction of CTR1 with ETR1, one of the ethylene receptors. The basic amino acid motif shown to be required for PA binding in Raf-1 is conserved in CTR1-K. However, mutations in this motif did not affect either PA-binding or PA-dependent inhibition of CTR1 activity. Subsequent deletion analysis of CTR1s kinase domain revealed a novel PA-binding region at the C-terminus of the kinase.
Key words: Constitutive triple response 1, ethylene, lipid signalling, phosphatidic acid, plant stress signalling, protein kinase
These authors contributed equally to this work. Received 3 August 2007; Revised 13 September 2007 Accepted 14 September 2007