title: Closely related receptor complexes differ in their ABA selectivity and sensitivity.
abstract: The recent discovery of a variety of receptors has led to new models for hormone perception in plants. In the case of the hormone abscisic acid (ABA), which regulates plant responses to abiotic stress, perception seems to occur both at the plasma membrane and in the cytosol. The cytosolic receptors for ABA have recently been identified as complexes between protein phosphatases 2C (PP2C) and regulatory components (RCAR/PYR/PYL) that bind ABA. Binding of ABA to the receptor complexes inactivates the PP2Cs, thereby activating the large variety of physiological processes regulated by ABA. The Arabidopsis genome encodes 13 homologues of RCAR1 and approximately 80 PP2Cs, of which six in clade A have been identified as negative regulators of ABA responses. In this study we characterize a novel member of the RCAR family, RCAR3. RCAR3 was identified in a screen for interactors of the PP2Cs ABI1 and ABI2, which are key regulators of ABA responses. RCAR3 was shown to repress ABI1 and ABI2 in vitro, and to stimulate ABA signalling in protoplast cells. RCAR3 conferred greater ABA sensitivity to the PP2C regulation than RCAR1, whereas stereo-selectivity for (S)-ABA was less stringent with RCAR3 as compared with RCAR1. In addition, regulation of the protein phosphatase activity by RCAR1 and RCAR3 was more sensitive to ABA for ABI1 than for ABI2. Based on the differences we have observed in transcriptional regulation and biochemical properties, we propose a model whereby differential expression of the co-receptors and combinatorial assembly of the receptor complexes act in concert to modulate and fine-tune ABA responses.
authors.affiliation: Lehrstuhl für Botanik, Technische Universität München, Am Hochanger 4, D-85354 Freising, Germany.
authors.forename: Izabela
authors.initials: I
authors.lastname: Szostkiewicz
authors.forename: Klaus
authors.initials: K
authors.lastname: Richter
authors.forename: Michal
authors.initials: M
authors.lastname: Kepka
authors.forename: Simone
authors.initials: S
authors.lastname: Demmel
authors.forename: Yue
authors.initials: Y
authors.lastname: Ma
authors.forename: Arthur
authors.initials: A
authors.lastname: Korte
authors.forename: Farhah F
authors.initials: FF
authors.lastname: Assaad
authors.forename: Alexander
authors.initials: A
authors.lastname: Christmann
authors.forename: Erwin
authors.initials: E
authors.lastname: Grill
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism / Q000502:physiology*; D002151:Calorimetry; D002352:Carrier Proteins; D002942:Circular Dichroism; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology; D047908:Intracellular Signaling Peptides and Proteins; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D000071636:Protein Phosphatase 2C; D011523:Protoplasts / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction; D020798:Two-Hybrid System Techniques
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; C540972:RCAR1 protein, Arabidopsis; D000040:Abscisic Acid; C087434:ABI1 protein, Arabidopsis; C106443:ABI2 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases; D000071636:Protein Phosphatase 2C