Shipman, Rebecca , Inoue, Kentaro .
Plastidic type I signal peptidase 1 has a functional role in both the envelope and thylakoids of Arabidopsis chloroplasts.
Type I signal peptidases (SPases I) are responsible for processing transported proteins in various membranes of prokaryotic and eukaryotic cells. Recently, we showed that Plastidic SPase 1 (Plsp1) is important for plastid biogenesis. Arabidopsis mutant plants lacking Plsp1, plsp1-1, were seedling lethal and showed a severe disruption of thylakoid development. Remarkably, the mutant plants accumulated intermediate forms of an outer envelope protein Toc75 and a thylakoidal protein OE33 (PsbO), indicating that Plsp1 may have roles in both the envelope and thylakoids. To further define the function of Plsp1, we isolated plastids from the plsp1-1 plants and examined their proteome. A nanoLC-MS/MS analysis showed that the mutant plastids accumulated many thylakoidal proteins. By immunoblotting, we found that levels of these proteins varied with respect to those in wildtype plastids. Furthermore, our data suggest that in addition to OE33 and Toc75, two thylakoidal proteins OE23 (PsbP) and plastocyanin, but not OE17 (PsbQ), are Plsp1 substrates. To substantiate the hypothesis that Plsp1 has a role in the envelope and thylakoids, we raised an antibody against Plsp1 and used it for electron microscope immunolocalization. The location of Plsp1 changed with plastid development; in proplastids it was equally distributed between envelopes and prothylakoids, while in mature chloroplasts it was only detectable in thylakoids. Furthermore, immunoblotting of protease-treated thylakoids showed that the catalytic site of Plsp1 is located in the thylakoid lumen. In summary, Plsp1 is a dual-localized protein with identified substrates that is essential for thylakoid development. It may prove to be a useful tool for studying plastid biogenesis.
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1 - University of California, Davis, Plant Sciences, 222 Asmundson Hall, One Shields Ave., Davis, Ca, 95616, USA
2 - University of California, Davis, Plant Sciences
chloroplast protein transport
Presentation Type: ASPB Minisymposium
Location: Continental A/Hilton
Date: Wednesday, July 11th, 2007
Time: 8:55 AM