Evolution of protein transport to the chloroplast envelope membranes
- 748 Downloads
Chloroplasts are descendants of an ancient endosymbiotic cyanobacterium that lived inside a eukaryotic cell. They inherited the prokaryotic double membrane envelope from cyanobacteria. This envelope contains prokaryotic protein sorting machineries including a Sec translocase and relatives of the central component of the bacterial outer membrane β-barrel assembly module. As the endosymbiont was integrated with the rest of the cell, the synthesis of most of its proteins shifted from the stroma to the host cytosol. This included nearly all the envelope proteins identified so far. Consequently, the overall biogenesis of the chloroplast envelope must be distinct from cyanobacteria. Envelope proteins initially approach their functional locations from the exterior rather than the interior. In many cases, they have been shown to use components of the general import pathway that also serves the stroma and thylakoids. If the ancient prokaryotic protein sorting machineries are still used for chloroplast envelope proteins, their activities must have been modified or combined with the general import pathway. In this review, we analyze the current knowledge pertaining to chloroplast envelope biogenesis and compare this to bacteria.
KeywordsChloroplast Endosymbiosis Envelope Protein sorting Transmembrane
- Hsu SC, Nafati M, Inoue K (2012) OEP80, an essential protein paralogous to the chloroplast protein translocation channel Toc75, exists as a 70-kD protein in the Arabidopsis thaliana chloroplast outer envelope. Plant Mol Biol 78:147–158. https://doi.org/10.1007/s11103-011-9853-2 CrossRefPubMedGoogle Scholar
- Inoue K, Potter D (2004) The chloroplastic protein translocation channel Toc75 and its paralog OEP80 represent two distinct protein families and are targeted to the chloroplastic outer envelope by different mechanisms. Plant J 39:354–365. https://doi.org/10.1111/j.1365-313X.2004.02135.x CrossRefPubMedGoogle Scholar
- Osteryoung KW, Pyke KA (2014) Division and dynamic morphology of plastids. Annu Rev Plant Biol 65:443–472. https://doi.org/10.1146/annurev-arplant-050213-035748 CrossRefPubMedGoogle Scholar
- Tripp J, Inoue K, Keegstra K, Froehlich JE (2007) A novel serine/proline-rich domain in combination with a transmembrane domain is required for the insertion of AtTic40 into the inner envelope membrane of chloroplasts. Plant J 52:824–838. https://doi.org/10.1111/j.1365-313X.2007.03279.x CrossRefPubMedGoogle Scholar