title: Quantitative phosphoproteomics identifies SnRK2 protein kinase substrates and reveals the effectors of abscisic acid action.
abstract: Sucrose nonfermenting 1 (SNF1)-related protein kinase 2s (SnRK2s) are central components of abscisic acid (ABA) signaling pathways. The snrk2.2/2.3/2.6 triple-mutant plants are nearly completely insensitive to ABA, suggesting that most of the molecular actions of ABA are triggered by the SnRK2s-mediated phosphorylation of substrate proteins. Only a few substrate proteins of the SnRK2s are known. To identify additional substrate proteins of the SnRK2s and provide insight into the molecular actions of ABA, we used quantitative phosphoproteomics to compare the global changes in phosphopeptides in WT and snrk2.2/2.3/2.6 triple mutant seedlings in response to ABA treatment. Among the 5,386 unique phosphorylated peptides identified in this study, we found that ABA can increase the phosphorylation of 166 peptides and decrease the phosphorylation of 117 peptides in WT seedlings. In the snrk2.2/2.3/2.6 triple mutant, 84 of the 166 peptides, representing 58 proteins, could not be phosphorylated, or phosphorylation was not increased under ABA treatment. In vitro kinase assays suggest that most of the 58 proteins can serve as substrates of the SnRK2s. The SnRK2 substrates include proteins involved in flowering time regulation, RNA and DNA binding, miRNA and epigenetic regulation, signal transduction, chloroplast function, and many other cellular processes. Consistent with the SnRK2 phosphorylation of flowering time regulators, the snrk2.2/2.3/2.6 triple mutant flowered significantly earlier than WT. These results shed new light on the role of the SnRK2 protein kinases and on the downstream effectors of ABA action, and improve our understanding of plant responses to adverse environments.
authors.affiliation: Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Pengcheng
authors.initials: P
authors.lastname: Wang
authors.forename: Liang
authors.initials: L
authors.lastname: Xue
authors.forename: Giorgia
authors.initials: G
authors.lastname: Batelli
authors.forename: Shinyoung
authors.initials: S
authors.lastname: Lee
authors.forename: Yueh-Ju
authors.initials: YJ
authors.lastname: Hou
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Van Oosten
authors.forename: Huiming
authors.initials: H
authors.lastname: Zhang
authors.forename: W Andy
authors.initials: WA
authors.lastname: Tao
authors.forename: Jian-Kang
authors.initials: JK
authors.lastname: Zhu
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism; D044127:Epigenesis, Genetic; D035264:Flowers / Q000254:growth & development / Q000378:metabolism; D017343:Genes, Plant; D009154:Mutation; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010937:Plant Growth Regulators / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D040901:Proteomics / Q000379:methods*; D015398:Signal Transduction / Q000235:genetics; D013379:Substrate Specificity / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D010750:Phosphoproteins; D010937:Plant Growth Regulators; C492978:SnRK2 protein, Arabidopsis; D000040:Abscisic Acid; D017346:Protein Serine-Threonine Kinases