title: Regulatory subunit B'gamma of protein phosphatase 2A prevents unnecessary defense reactions under low light in Arabidopsis.
abstract: Light is an important environmental factor that modulates acclimation strategies and defense responses in plants. We explored the functional role of the regulatory subunit B'γ (B'γ) of protein phosphatase 2A (PP2A) in light-dependent stress responses of Arabidopsis (Arabidopsis thaliana). The predominant form of PP2A consists of catalytic subunit C, scaffold subunit A, and highly variable regulatory subunit B, which determines the substrate specificity of PP2A holoenzymes. Mutant leaves of knockdown pp2a-b'γ plants show disintegration of chloroplasts and premature yellowing conditionally under moderate light intensity. The cell-death phenotype is accompanied by the accumulation of hydrogen peroxide through a pathway that requires CONSTITUTIVE EXPRESSION OF PR GENES5 (CPR5). Moreover, the pp2a-b'γ cpr5 double mutant additionally displays growth suppression and malformed trichomes. Similar to cpr5, the pp2a-b'γ mutant shows constitutive activation of both salicylic acid- and jasmonic acid-dependent defense pathways. In contrast to cpr5, however, pp2a-b'γ leaves do not contain increased levels of salicylic acid or jasmonic acid. Rather, the constitutive defense response associates with hypomethylation of DNA and increased levels of methionine-salvage pathway components in pp2a-b'γ leaves. We suggest that the specific B'γ subunit of PP2A is functionally connected to CPR5 and operates in the basal repression of defense responses under low irradiance.
authors.affiliation: Department of Biochemistry and Food Chemistry, University of Turku, FI-20014 Turku, Finland.
authors.forename: Andrea
authors.initials: A
authors.lastname: Trotta
authors.forename: Michael
authors.initials: M
authors.lastname: Wrzaczek
authors.forename: Judith
authors.initials: J
authors.lastname: Scharte
authors.forename: Mikko
authors.initials: M
authors.lastname: Tikkanen
authors.forename: Grzegorz
authors.initials: G
authors.lastname: Konert
authors.forename: Moona
authors.initials: M
authors.lastname: Rahikainen
authors.forename: Maija
authors.initials: M
authors.lastname: Holmström
authors.forename: Hanna-Maija
authors.initials: HM
authors.lastname: Hiltunen
authors.forename: Stephan
authors.initials: S
authors.lastname: Rips
authors.forename: Nina
authors.initials: N
authors.lastname: Sipari
authors.forename: Paula
authors.initials: P
authors.lastname: Mulo
authors.forename: Engelbert
authors.initials: E
authors.lastname: Weis
authors.forename: Antje
authors.initials: A
authors.lastname: von Schaewen
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
authors.forename: Saijaliisa
authors.initials: S
authors.lastname: Kangasjärvi
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000276:immunology* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D015139:Blotting, Southern; D019175:DNA Methylation / Q000235:genetics / Q000528:radiation effects; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D055785:Gene Knockdown Techniques; D008027:Light; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D058503:Mesophyll Cells / Q000166:cytology / Q000528:radiation effects / Q000648:ultrastructure; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D010748:Phosphopeptides / Q000737:chemistry / Q000378:metabolism; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D040901:Proteomics; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C528008:CPR5 protein, Arabidopsis; D008565:Membrane Proteins; D010748:Phosphopeptides; D021122:Protein Subunits; D017382:Reactive Oxygen Species; D054648:Protein Phosphatase 2