In vivo assessment of the significance of phosphorylation of the Arabidopsis chloroplast protein import receptor, atToc33.
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.
Aronsson
Henrik
H
Department of Plant and Environmental Sciences, Göteborg University, Box 461, SE-405 30 Göteborg, Sweden.
Combe
Jonathan
J
Patel
Ramesh
R
Jarvis
Paul
P
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
D029681:Arabidopsis Proteins; D008565:Membrane Proteins; C114786:Toc33 protein, Arabidopsis