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PYR/PYL/RCAR family members are major in-vivo ABI1 protein phosphatase 2C-interacting proteins in Arabidopsis.

ABSTRACT: Abscisic acid (ABA) mediates resistance to abiotic stress and controls developmental processes in plants. The group-A PP2Cs, of which ABI1 is the prototypical member, are protein phosphatases that play critical roles as negative regulators very early in ABA signal transduction. Because redundancy is thought to limit the genetic dissection of early ABA signalling, to identify redundant and early ABA signalling proteins, we pursued a proteomics approach. We generated YFP-tagged ABI1 Arabidopsis expression lines and identified in vivo ABI1-interacting proteins by mass-spectrometric analyses of ABI1 complexes. Known ABA signalling components were isolated including SnRK2 protein kinases. We confirm previous studies in yeast and now show that ABI1 interacts with the ABA-signalling kinases OST1, SnRK2.2 and SnRK2.3 in plants. Interestingly, the most robust in planta ABI1-interacting proteins in all LC-MS/MS experiments were nine of the 14 PYR/PYL/RCAR proteins, which were recently reported as ABA-binding signal transduction proteins, providing evidence for in vivo PYR/PYL/RCAR interactions with ABI1 in Arabidopsis. ABI1-PYR1 interaction was stimulated within 5 min of ABA treatment in Arabidopsis. Interestingly, in contrast, PYR1 and SnRK2.3 co-immunoprecipitated equally well in the presence and absence of ABA. To investigate the biological relevance of the PYR/PYLs, we analysed pyr1/pyl1/pyl2/pyl4 quadruple mutant plants and found strong insensitivities in ABA-induced stomatal closure and ABA-inhibition of stomatal opening. These findings demonstrate that ABI1 can interact with several PYR/PYL/RCAR family members in Arabidopsis, that PYR1-ABI1 interaction is rapidly stimulated by ABA in Arabidopsis and indicate new SnRK2 kinase-PYR/PYL/RCAR interactions in an emerging model for PYR/PYL/RCAR-mediated ABA signalling.

SUBMITTER: Nishimura N

PROVIDER: S-EPMC2807913 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:ABA signaling relies on the perception of the hormone by 14 different members of the PYR/PYL/RCAR family of ABA receptors. Upon ABA binding, receptors become active in inhibiting a family of type 2C protein phosphatases that usually function as negative regulators on protein kinases of the SnRK2 family. Previous physiological and genetic data supporting a negative role exerted by nitric oxide (NO) on ABA signaling have been reported. Our preliminary data suggested that negative regulation exerted by NO on ABA signaling may involve direct effects of NO on ABA receptors. Here we explore whether the effects of NO on ABA signaling are due to post-translational modifications (PTMs) on ABA receptors. Two main PTMs are functionally related to NO, the S-nitrosylation of C residues and the nitration of Y residues and they have been studied in this work. Because our data suggest that NO can also modulate the stability of the receptor proteins, we have also analyzed another PTM, the ubiquitination of K residues. A double approach based on in vitro nitration of recombinant PYR/PYL/RCAR proteins as well as in planta expression of HA-tagged versions of the receptors, followed by immunopurification strategies based on anti-3-nitroY-coated magnetic beads, and LC-MS/MS analyses of the immunopurified proteins under non-reducing conditions allowed us to identify peptides containing nitroY (mass shifts of +45), S-nitrosylated C (mass shifts of +29), and K-GG tags resulting from the trypsin digestion of ubiquitin tails (mass shift of + 114). Our data suggest that S-nitrosylation of cysteines from PYR/PYL receptors occur in planta but has not effect on receptor function as tested in vitro. By contrast, the nitration of several Y residues of PYR/PYL receptors completely inactivates them, promotes also their polyubiquitination and marks them for subsequent proteasomal degradation, thus representing a rapid mechanism for lowering ABA sensitivity when required in the plant.

Project description:Abscisic acid (ABA) is a key hormone for plant growth, development and stress adaptation. Perception of ABA through four types of receptors has been reported. We show here that impairment of ABA perception through the PYR/PYL/RCAR branch reduces vegetative growth and seed production, and leads to a severely open stomata and dramatic ABA insensitive phenotype, even though other branches for ABA perception remain functional. Arabidopsis sextuple mutant impaired in 6 PYR/PYL receptors, namely PYR1, PYL1, PYL2, PYL4, PYL5 and PYL8, was able to germinate and grow even on 100 mM ABA. Whole-rosette stomatal conductance (Gst) measurements revealed that leaf transpiration in the sextuple pyr/pyl mutant was higher than in the ABA-deficient aba3-1 or ABA-insensitive snrk2.6 mutants. The gradually increasing Gst values of plants lacking three, four, five and six PYR/PYLs indicate quantitative regulation of stomatal aperture by this family of receptors. The sextuple mutant lacked ABA-mediated activation of SnRK2s and ABA-responsive gene expression was dramatically impaired as was reported in snrk2.2/2.3/2.6. In summary, these results show that ABA perception by PYR/PYLs plays a major role to regulate seed germination and establishment, basal ABA signaling required for vegetative and reproductive growth, stomatal aperture and transcriptional response to the hormone. Four biological replicates were generated for the 3 genotypes, pyr1pyl1pyl2pyl4pyl5pyl8 sextuple mutant, snrk2.2/2.3/2.6 triple mutant, and Col-0. All the samples were treated with ABA for 3 hours before harvesting. The four Col-0 samples were mix to create an unique reference Col-0 sample. Two comparasion were made, fisrt one, PYR/PYL sextuple mutant versus Col-0 reference sample and second one, SnRK2 triple mutant versus Col-0 reference sample. In each comparasion four biological replicates were made. Replicas number 1 and 2 were labeled with Cy5 for the mutant sample and Cy3 for the Col-0 reference sample, while the other two replicas,#3 and #4, were reversed-labeled.

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PYR/PYL/RCAR family members are major in-vivo ABI1 protein phosphatase 2C-interacting proteins in Arabidopsis.

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