title: Mitogen-activated protein kinase 4 is a salicylic acid-independent regulator of growth but not of photosynthesis in Arabidopsis.
abstract: Mitogen-activated protein kinase (MAPK) pathways regulate signal transduction from different cellular compartments and from the extracellular environment to the nucleus in all eukaryotes. One of the best-characterized MAPKs in Arabidopsis thaliana is MPK4, which was shown to be a negative regulator of systemic-acquired resistance. The mpk4 mutant accumulates salicylic acid (SA), possesses constitutive expression of pathogenesis-related (PR) genes, and has an extremely dwarf phenotype. We show that suppression of SA and phylloquinone synthesis in chloroplasts by knocking down the ICS1 gene (by crossing it with the ics1 mutant) in the mpk4 mutant background did not revert mpk4-impaired growth. However, it did cause changes in the photosynthetic apparatus and severely impaired the quantum yield of photosystem II. Transmission microscopy analysis revealed that the chloroplasts' structure was strongly altered in the mpk4 and mpk4/ics1 double mutant. Analysis of reactive oxygen species (ROS)-scavenging enzymes expression showed that suppression of SA and phylloquinone synthesis in the chloroplasts of the mpk4 mutant caused imbalances in ROS homeostasis which were more pronounced in mpk4/ics1 than in mpk4. Taken together, the presented results strongly suggest that MPK4 is an ROS/hormonal rheostat hub that negatively, in an SA-dependent manner, regulates immune defenses, but at the same time positively regulates photosynthesis, ROS metabolism, and growth. Therefore, we concluded that MPK4 is a complex regulator of chloroplastic retrograde signaling for photosynthesis, growth, and immune defenses in Arabidopsis.
authors.affiliation: Department of Plant Genetics, Breeding and Biotechnology, Faculty of Horticulture and Landscape Architecture, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, Warsaw, 02-776, Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Gawroński
authors.affiliation: Department of Plant Genetics, Breeding and Biotechnology, Faculty of Horticulture and Landscape Architecture, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, Warsaw, 02-776, Poland.
authors.forename: Damian
authors.initials: D
authors.lastname: Witoń
authors.affiliation: Department of Plant Genetics, Breeding and Biotechnology, Faculty of Horticulture and Landscape Architecture, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, Warsaw, 02-776, Poland.
authors.forename: Kateryna
authors.initials: K
authors.lastname: Vashutina
authors.affiliation: Department of Botany, Faculty of Agriculture and Biology, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, Warsaw, 02-776, Poland.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Bederska
authors.affiliation: Department of Plant Genetics, Breeding and Biotechnology, Faculty of Horticulture and Landscape Architecture, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, Warsaw, 02-776, Poland.
authors.forename: Błażej
authors.initials: B
authors.lastname: Betliński
authors.affiliation: Department of Plant Genetics, Breeding and Biotechnology, Faculty of Horticulture and Landscape Architecture, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, Warsaw, 02-776, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Rusaczonek
authors.affiliation: Department of Plant Genetics, Breeding and Biotechnology, Faculty of Horticulture and Landscape Architecture, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, Warsaw, 02-776, Poland stanislaw_karpinski@sggw.pl.
authors.forename: Stanisław
authors.initials: S
authors.lastname: Karpiński
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000201:enzymology* / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D018506:Gene Expression Regulation, Plant; D006706:Homeostasis; D019751:Intramolecular Transferases / Q000235:genetics / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010641:Phenotype; D010788:Photosynthesis; D017382:Reactive Oxygen Species / Q000378:metabolism; D020156:Salicylic Acid / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; D017382:Reactive Oxygen Species; C436292:AtMPK4 protein, Arabidopsis; D020928:Mitogen-Activated Protein Kinases; D019751:Intramolecular Transferases; C058486:isochorismate synthase; D020156:Salicylic Acid
keywords: chloroplast ultrastructure; growth and photosynthesis regulation; phylloquinone; reactive oxygen species (ROS); retrograde signaling and salicylic acid (SA).