title: In vivo assessment of the significance of phosphorylation of the Arabidopsis chloroplast protein import receptor, atToc33.
abstract: atToc33 is a transit peptide receptor of the chloroplast outer envelope membrane, and possesses GTPase activity. In vitro, its transit peptide- and GTP-binding properties are abrogated by its phosphorylation at serine 181, which was proposed to represent an important regulatory mechanism. We mutated S181 to alanine (to prevent phosphorylation), and to aspartate and glutamate (to mimic the effects of phosphoserine), and expressed all three proteins in ppi1 (atToc33 knockout) plants using the native promoter. The mutants complemented ppi1 with equal efficiency in respect of all criteria tested, including protein import efficiency and light stress tolerance. The data suggest that atToc33 phosphorylation may not play an important role in vivo.
authors.affiliation: Department of Plant and Environmental Sciences, Göteborg University, Box 461, SE-405 30 Göteborg, Sweden.
authors.forename: Henrik
authors.initials: H
authors.lastname: Aronsson
authors.forename: Jonathan
authors.initials: J
authors.lastname: Combe
authors.forename: Ramesh
authors.initials: R
authors.lastname: Patel
authors.forename: Paul
authors.initials: P
authors.lastname: Jarvis
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism* / Q000648:ultrastructure; D005838:Genotype; D008027:Light; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010641:Phenotype; D010766:Phosphorylation; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic
chemical_list: D029681:Arabidopsis Proteins; D008565:Membrane Proteins; C114786:Toc33 protein, Arabidopsis