title: Release of GTP Exchange Factor Mediated Down-Regulation of Abscisic Acid Signal Transduction through ABA-Induced Rapid Degradation of RopGEFs.
abstract: The phytohormone abscisic acid (ABA) is critical to plant development and stress responses. Abiotic stress triggers an ABA signal transduction cascade, which is comprised of the core components PYL/RCAR ABA receptors, PP2C-type protein phosphatases, and protein kinases. Small GTPases of the ROP/RAC family act as negative regulators of ABA signal transduction. However, the mechanisms by which ABA controls the behavior of ROP/RACs have remained unclear. Here, we show that an Arabidopsis guanine nucleotide exchange factor protein RopGEF1 is rapidly sequestered to intracellular particles in response to ABA. GFP-RopGEF1 is sequestered via the endosome-prevacuolar compartment pathway and is degraded. RopGEF1 directly interacts with several clade A PP2C protein phosphatases, including ABI1. Interestingly, RopGEF1 undergoes constitutive degradation in pp2c quadruple abi1/abi2/hab1/pp2ca mutant plants, revealing that active PP2C protein phosphatases protect and stabilize RopGEF1 from ABA-mediated degradation. Interestingly, ABA-mediated degradation of RopGEF1 also plays an important role in ABA-mediated inhibition of lateral root growth. The presented findings point to a PP2C-RopGEF-ROP/RAC control loop model that is proposed to aid in shutting off ABA signal transduction, to counteract leaky ABA signal transduction caused by "monomeric" PYL/RCAR ABA receptors in the absence of stress, and facilitate signaling in response to ABA.
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, California, United States of America.|Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Zixing
authors.identifier: 0000-0002-2692-9008
authors.initials: Z
authors.lastname: Li
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, California, United States of America.
authors.forename: Rainer
authors.initials: R
authors.lastname: Waadt
authors.affiliation: Division of Biological Sciences, Cell and Developmental Biology Section, University of California San Diego, La Jolla, California, United States of America.
authors.forename: Julian I
authors.initials: JI
authors.lastname: Schroeder
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism* / Q000494:pharmacology; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002451:Cell Compartmentation / Q000187:drug effects; D004843:Epistasis, Genetic; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism; D030821:Plants, Genetically Modified; D021381:Protein Transport / Q000187:drug effects; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; D020662:Guanine Nucleotide Exchange Factors; C553927:RopGEF1 protein, Arabidopsis; D000040:Abscisic Acid; C087434:ABI1 protein, Arabidopsis; C106443:ABI2 protein, Arabidopsis; C463465:AHG3 protein, Arabidopsis; C514757:HAB1 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases