title: Comparative phosphoproteome profiling reveals a function of the STN8 kinase in fine-tuning of cyclic electron flow (CEF).
abstract: Important aspects of photosynthetic electron transport efficiency in chloroplasts are controlled by protein phosphorylation. Two thylakoid-associated kinases, STN7 and STN8, have distinct roles in short- and long-term photosynthetic acclimation to changes in light quality and quantity. Although some substrates of STN7 and STN8 are known, the complexity of this regulatory kinase system implies that currently unknown substrates connect photosynthetic performance with the regulation of metabolic and regulatory functions. We performed an unbiased phosphoproteome-wide screen with Arabidopsis WT and stn8 mutant plants to identify unique STN8 targets. The phosphorylation status of STN7 was not affected in stn8, indicating that kinases other than STN8 phosphorylate STN7 under standard growth conditions. Among several putative STN8 substrates, PGRL1-A is of particular importance because of its possible role in the modulation of cyclic electron transfer. The STN8 phosphorylation site on PGRL1-A is absent in both monocotyledonous plants and algae. In dicots, spectroscopic measurements with Arabidopsis WT, stn7, stn8, and stn7/stn8 double-mutant plants indicate a STN8-mediated slowing down of the transition from cyclic to linear electron flow at the onset of illumination. This finding suggests a possible link between protein phosphorylation by STN8 and fine-tuning of cyclic electron flow during this critical step of photosynthesis, when the carbon assimilation is not commensurate to the electron flow capacity of the chloroplast.
authors.affiliation: Department of Biology, Eidgenössische Technische Hochschule Zurich, 8092 Zurich, Switzerland.
authors.forename: Sonja
authors.initials: S
authors.lastname: Reiland
authors.forename: Giovanni
authors.initials: G
authors.lastname: Finazzi
authors.forename: Anne
authors.initials: A
authors.lastname: Endler
authors.forename: Adrian
authors.initials: A
authors.lastname: Willig
authors.forename: Katja
authors.initials: K
authors.lastname: Baerenfaller
authors.forename: Jonas
authors.initials: J
authors.lastname: Grossmann
authors.forename: Bertran
authors.initials: B
authors.lastname: Gerrits
authors.forename: Dorothea
authors.initials: D
authors.lastname: Rutishauser
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Gruissem
authors.forename: Jean-David
authors.initials: JD
authors.lastname: Rochaix
authors.forename: Sacha
authors.initials: S
authors.lastname: Baginsky
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D002852:Chromatography, Ion Exchange; D002853:Chromatography, Liquid; D004579:Electron Transport; D008027:Light; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010750:Phosphoproteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D010788:Photosynthesis / Q000235:genetics / Q000528:radiation effects; D045331:Photosystem I Protein Complex / Q000235:genetics / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D040901:Proteomics / Q000379:methods*; D017386:Sequence Homology, Amino Acid; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D029681:Arabidopsis Proteins; D008565:Membrane Proteins; C527375:PGRL1 protein, Arabidopsis; D010750:Phosphoproteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; C497212:STN7 protein, Arabidopsis; C504925:STN8 protein, Arabidopsis