title: The Arabidopsis mitogen-activated protein kinase phosphatase PP2C5 affects seed germination, stomatal aperture, and abscisic acid-inducible gene expression.
abstract: Abscisic acid (ABA) is an important phytohormone regulating various cellular processes in plants, including stomatal opening and seed germination. Although protein phosphorylation via mitogen-activated protein kinases (MAPKs) has been suggested to be important in ABA signaling, the corresponding phosphatases are largely unknown. Here, we show that a member of the Protein Phosphatase 2C (PP2C) family in Arabidopsis (Arabidopsis thaliana), PP2C5, is acting as a MAPK phosphatase. The PP2C5 protein colocalizes and directly interacts with stress-induced MPK3, MPK4, and MPK6, predominantly in the nucleus. Importantly, altered PP2C5 levels affect MAPK activation. Whereas Arabidopsis plants depleted of PP2C5 show an enhanced ABA-induced activation of MPK3 and MPK6, ectopic expression of PP2C5 in tobacco (Nicotiana benthamiana) resulted in the opposite effect, with the two MAPKs salicylic acid-induced protein kinase and wound-induced protein kinase not being activated any longer after ABA treatment. Moreover, depletion of PP2C5, whose gene expression itself is affected by ABA treatment, resulted in altered ABA responses. Loss-of-function mutation in PP2C5 or AP2C1, a close PP2C5 homolog, resulted in an increased stomatal aperture under normal growth conditions and a partial ABA-insensitive phenotype in seed germination that was most prominent in the pp2c5 ap2c1 double mutant line. In addition, the response of ABA-inducible genes such as ABI1, ABI2, RD29A, and Erd10 was reduced in the mutant plants. Thus, we suggest that PP2C5 acts as a MAPK phosphatase that positively regulates seed germination, stomatal closure, and ABA-inducible gene expression.
authors.affiliation: Center for Plant Molecular Biology, Plant Biochemistry, Eberhard Karls University of Tübingen, 72076 Tuebingen, Germany.
authors.forename: Anita K
authors.initials: AK
authors.lastname: Brock
authors.forename: Roland
authors.initials: R
authors.lastname: Willmann
authors.forename: Dagmar
authors.initials: D
authors.lastname: Kolb
authors.forename: Laure
authors.initials: L
authors.lastname: Grefen
authors.forename: Heini M
authors.initials: HM
authors.lastname: Lajunen
authors.forename: Gerit
authors.initials: G
authors.lastname: Bethke
authors.forename: Justin
authors.initials: J
authors.lastname: Lee
authors.forename: Thorsten
authors.initials: T
authors.lastname: Nürnberger
authors.forename: Andrea A
authors.initials: AA
authors.lastname: Gust
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000187:drug effects / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D055786:Gene Knockout Techniques; D018525:Germination / Q000187:drug effects*; D054639:Mitogen-Activated Protein Kinase Phosphatases / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D054046:Plant Stomata / Q000033:anatomy & histology* / Q000187:drug effects / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D012639:Seeds / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000254:growth & development*; D013312:Stress, Physiological / Q000187:drug effects / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D000040:Abscisic Acid; C552542:PP2C5 protein, Arabidopsis; D054639:Mitogen-Activated Protein Kinase Phosphatases