Characterization of a T-DNA insertion mutant for the protein import receptor atToc33 from chloroplasts.
In Arabidopsis thaliana, the Toc34 receptor component of the chloroplast import machinery is encoded by two independent but highly homologous genes, atToc33 and atToc34. We have isolated a T-DNA insertion mutant of atToc33 which is characterized by a pale phenotype, due to reductions in the levels of photosynthetic pigments, and alterations in protein composition. The latter involve not only chloroplast proteins but also some cytosolic polypeptides, including 14-3-3 proteins which, among other functions, have been proposed to be cytosolic targeting factors for nucleus-encoded chloroplast proteins. Within the chloroplast, many, though not all, proteins of the photosynthetic apparatus, as well as proteins not directly involved in photosynthesis, are found in significantly reduced amounts in the mutant. However, the accumulation of other chloroplast proteins is unaffected. This suggests that the atToc33 receptor is responsible for the import of a specific subset of nucleus-encoded chloroplast proteins. Supporting evidence for this conclusion was obtained by antisense repression of the atToc34 gene in the atToc33 mutant, which results in an exacerbation of the phenotype.
Gutensohn
M
M
Institut für Pflanzenphysiologie, Martin-Luther-Universität Halle-Wittenberg, Weinbergweg 10, 06120 Halle, Germany. gutensohn@pflanzenphys.uni-halle.de
Pahnke
S
S
Kolukisaoglu
U
U
Schulz
B
B
Schierhorn
A
A
Voigt
A
A
Hust
B
B
Rollwitz
I
I
Stöckel
J
J
Geimer
S
S
Albrecht
V
V
Flügge
U I
UI
Klösgen
R B
RB
D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics*; D015152:Blotting, Northern; D015139:Blotting, Southern; D015153:Blotting, Western; D002338:Carotenoids / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000235:genetics* / Q000648:ultrastructure; D003001:Cloning, Molecular; D017931:DNA Primers; D004269:DNA, Bacterial / Q000235:genetics*; D005453:Fluorescence; D040461:Gene Components; D005822:Genetic Vectors; D013058:Mass Spectrometry; D008565:Membrane Proteins / Q000235:genetics*; D046529:Microscopy, Electron, Transmission; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D020133:Reverse Transcriptase Polymerase Chain Reaction
D029681:Arabidopsis Proteins; D017931:DNA Primers; D004269:DNA, Bacterial; D008565:Membrane Proteins; C036483:T-DNA; C114786:Toc33 protein, Arabidopsis; D002734:Chlorophyll; D002338:Carotenoids