Functional Specialization amongst the Arabidopsis Toc159 Family of Chloroplast Protein Import ReceptorsW⃞
AUTOR(ES)
Kubis, Sybille
FONTE
American Society of Plant Biologists
RESUMO
The initial stages of preprotein import into chloroplasts are mediated by the receptor GTPase Toc159. In Arabidopsis thaliana, Toc159 is encoded by a small gene family: atTOC159, atTOC132, atTOC120, and atTOC90. Phylogenetic analysis suggested that at least two distinct Toc159 subtypes, characterized by atToc159 and atToc132/atToc120, exist in plants. atTOC159 was strongly expressed in young, photosynthetic tissues, whereas atTOC132 and atTOC120 were expressed at a uniformly low level and so were relatively prominent in nonphotosynthetic tissues. Based on the albino phenotype of its knockout mutant, atToc159 was previously proposed to be a receptor with specificity for photosynthetic preproteins. To elucidate the roles of the other isoforms, we characterized Arabidopsis knockout mutants for each one. None of the single mutants had strong visible phenotypes, but toc132 toc120 double homozygotes appeared similar to toc159, indicating redundancy between atToc132 and atToc120. Transgenic complementation studies confirmed this redundancy but revealed little functional overlap between atToc132/atToc120 and atToc159 or atToc90. Unlike toc159, toc132 toc120 caused structural abnormalities in root plastids. Furthermore, when proteomics and transcriptomics were used to compare toc132 with ppi1 (a receptor mutant that is specifically defective in the expression, import, and accumulation of photosynthetic proteins), major differences were observed, suggesting that atToc132 (and atToc120) has specificity for nonphotosynthetic proteins. When both atToc159 and the major isoform of the other subtype, atToc132, were absent, an embryo-lethal phenotype resulted, demonstrating the essential role of Toc159 in the import mechanism.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=519198Documentos Relacionados
- Members of the Toc159 Import Receptor Family Represent Distinct Pathways for Protein Targeting to Plastids
- Initial Binding of Preproteins Involving the Toc159 Receptor Can Be Bypassed during Protein Import into Chloroplasts1
- Chloroplast Protein Translocon Components atToc159 and atToc33 Are Not Essential for Chloroplast Biogenesis in Guard Cells and Root Cells1
- The Yeast Saccharomyces cerevisiae Is Not an Efficient Tool for in Vivo Studies of Plant Vacuolar Sorting ReceptorsW⃞
- Import Pathways of Chloroplast Interior Proteins and the Outer-Membrane Protein OEP14 Converge at Toc75