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DEVELOPMENT AND HORMONE ACTION

Triple Loss of Function of Protein Phosphatases Type 2C Leads to Partial Constitutive Response to Endogenous Abscisic Acid^{1,[C],[W],[OA]}

Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia-Consejo Superior de Investigaciones Científicas, ES–46022 Valencia, Spain (S.R., A.R., A.S., J.S., P.L.R.); Cell and Developmental Biology Section, Division of Biological Sciences, and Center for Molecular Genetics, University of California, La Jolla, California 92093–0116 (M.B.D., T.-H.K., J.I.S.); and Department of Biology, Universitat de les Illes Balears, ES–07122 Palma de Mallorca, Spain (A.G., J.F.)

The phytohormone abscisic acid (ABA) is a key regulator of plant growth and development as well as plant responses to situations of decreased water availability. Protein phosphatases type 2C (PP2Cs) from group A, which includes the ABI1/HAB1 and PP2CA branches, are key negative regulators of ABA signaling. Specifically, HAB1, ABI1, ABI2, and PP2CA have been shown to affect both seed and vegetative responses to ABA. To further understand their contribution to ABA signaling and to unravel possible genetic interactions and functional redundancy among them, we have generated different combinations of double and triple mutants impaired in these PP2Cs. Interestingly, hab1-1pp2ca-1 and abi1-2pp2ca-1 double mutants showed reduced water loss and enhanced resistance to drought stress, which further supports the role of PP2CA in vegetative responses to ABA. Two triple hab1-1abi1-2abi2-2 and hab1-1abi1-2pp2ca-1 mutants were generated, which showed an extreme response to exogenous ABA, impaired growth, and partial constitutive response to endogenous ABA. Thus, transcriptomic analysis revealed a partial up-regulation/down-regulation of a subset of ABA-responsive genes in both triple mutants in the absence of exogenous ABA. Comparison of ABA responses in the different pp2c mutants showed that a progressive increase in ABA sensitivity could be obtained through combined inactivation of these PP2Cs. These results indicate that ABA response is finely tuned by the integrated action of these genes, which is required to prevent a constitutive response to endogenous ABA that might have a deleterious effect on growth and development in the absence of environmental stress.

² These authors contributed equally to the article.

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: Pedro L. Rodriguez (prodriguez{at}ibmcp.upv.es).

^[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.

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www.plantphysiol.org/cgi/doi/10.1104/pp.109.137174

^* Corresponding author; e-mail prodriguez{at}ibmcp.upv.es.

Received February 24, 2009; accepted May 15, 2009; published May 20, 2009.