Suchergebnisse

SnRK2 kinases, PP2C phosphatases and the PYR/PYL/RCAR receptors constitute the core abscisic acid (ABA) signaling module that is thought to contain all of the intrinsic properties to self-regulate the hormone signal output. Here we identify Casein Kinase (CK)2 as a novel negative regulator of SnRK2. CK2 phosphorylates a cluster of conserved serines at the ABA box of SnRK2, increasing its binding to PP2C and triggering protein degradation. Consequently, CK2 action has implications on SnRK2 protein levels, as well as kinase activity and its response to abiotic stimuli. ; This work was supported by MCYT, Spain (Consolider-Ingenio 2010CSD2007-00036, BIO2009-13044); Comissionat per Universitats i Recerca de la Generalitat de Catalunya (CIRIT2009SGR626); Fundação para a Ciência e Tecnologia (PhD grant SFRH/BD/62070/2009); and European Union Marie-Curie (Early Stage Training Fellowships MEST-CT-2005-020232-2 ADONIS). ; Peer reviewed

9 pages, 7 figures.-- PMID: 16766669 [PubMed].-- PMCID: PMC1533959.-- Printed version Aug 2006. ; Rumex palustris (polygonceae) responds to complete submergence with enhanced elongation of its youngest petioles. This process requires the presence of gibberellin (GA) and is associated with an increase in the concentration of GA1 in elongating petioles.We have examined how GAbiosynthesis was regulated in submerged plants. Therefore, cDNAs encoding GA-biosynthetic enzymes GA20-oxidase andGA3-oxidase, and the GA-deactivating enzymeGA2-oxidase were cloned from R. palustris and the kinetics of transcription of the corresponding genes was determined during a 24 h submergence period. The submergence-induced elongation response could be separated into several phases: (1) during the first phase of 4 h, petiole elongation was insensitive to GA; (2) from 4 to 6 h onward growth was limited by GA; and (3) from 15 h onward underwater elongation was dependent, but not limited by GA. Submergence induced an increase of GA1 concentration, as well as enhanced transcript levels of RpGA3ox1. Exogenous abscisic acid repressed the transcript levels of RpGA20ox1 and RpGA3ox1 and thus inhibited the submergence-induced increase in GA1. Abscisic acid had no effect on the tissue responsiveness to GA. ; This work was supported by the Dutch Science Foundation (PIONIER grant no. 800.84.470) and by a grant from the European Union (HPRM–CT–RTN1–2000–00090). ; Peer reviewed

[EN] Abscisic acid (ABA) is an essential hormone for plant development and stress responses. ABA signaling is suppressed by clade A PP2C phosphatases, which function as key repressors of this pathway through inhibiting ABA-activated SnRK2s (SNF1-related protein kinases). Upon ABA perception, the PYR/PYL/RCAR ABA receptors bind to PP2Cs with high affinity and biochemically inhibit their activity. While thismechanismhas been extensively studied, how PP2Cs are regulated at the protein level is only starting to be explored. Arabidopsis thaliana RING DOMAIN LIGASE5 (RGLG5) belongs to a five-member E3 ubiquitin ligase family whose target proteins remain unknown. We report that RGLG5, together with RGLG1, releases the PP2C blockade of ABA signaling by mediating PP2CA protein degradation. ABA promotes the interaction of PP2CA with both E3 ligases, which mediate ubiquitination of PP2CA and are required for ABA-dependent PP2CA turnover. Downregulation of RGLG1 and RGLG5 stabilizes endogenous PP2CA and diminishes ABA-mediated responses. Moreover, the reduced response to ABA in germination assays is suppressed in the rglg1 amiR (artificial microRNA)-rglg5 pp2ca-1 triple mutant, supporting a functional link among these loci. Overall, our data indicate that RGLG1 and RGLG5 are important modulators of ABA signaling, and they unveil amechanismfor activation of the ABA pathway by controlling PP2C half-life. ; We thank Andreas Bachmair for the rglg1 mutant, Sean R. Cutler for the pyr1 pyl1 pyl2 pyl4 seeds, Dapeng Zhang for the transgenic material harboring ABI2, Hongwei Guo and Jianmin Zhou for the pCAMBIA1300-Nluc and pCAMBIA1300-Cluc vectors, and John Olson for assistance in English editing. Work in C.A.'s laboratory was supported by grants from the National Key Basic Science "973" Program (Grant 2012CB114006), the National Natural Science Foundation (Grants 31272023, 31170231, and 90817001) of the Chinese government, and by the State Key Laboratory of Protein and Plant Gene Research, Peking University. Work in P.L.R.'s ...