An RK/ST C-terminal motif is required for targeting of OEP7.2 and a subset of other Arabidopsis tail-anchored proteins to the plastid outer envelope membrane

Authors: TERESINSKI, HOWARD - University Of Guelph; GIDDA, SATINDER - University Of Guelph; NHUYEN, THUY - University Of Guelph; HOWARD, MARTY - University Of Guelph; PORTER, BRITTANY - Wilfrid Laurier University; GRIMBERG, NICHOLAS - Wilfrid Laurier University; SMITH, MATTHEW - Wilfrid Laurier University; ANDREWS, DAVID - University Of Toronto; Dyer, John; MULLEN, ROBERT - University Of Guelph

Submitted to: Plant and Cell Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2018
Publication Date: 12/5/2018
Citation: Teresinski, H.J., Gidda, S.K., Nhuyen, T.N., Howard, M., Porter, B.K., Grimberg, N., Smith, M.D., Andrews, D.W., Dyer, J.M., Mullen, R.T. 2018. An RK/ST C-terminal motif is required for targeting of OEP7.2 and a subset of other Arabidopsis tail-anchored proteins to the plastid outer envelope membrane. Plant and Cell Physiology. 60:516-537. https://doi.org/10.1093/pcp/pcy234.
DOI: https://doi.org/10.1093/pcp/pcy234

Interpretive Summary: The cells of all living organisms are in a constant state of renewal, continuously replacing parts that have broken down or building new structures to perform needed biological functions. One of the greatest challenges of modern cell biology is to figure out how the various organelles in a cell are put together. Much like the construction jobs in modern cities, the necessary building materials must first be transported to the correct job site where they are subsequently assembled into the final form. In the current manuscript, scientists at the ARS lab in Maricopa, the University of Guelph, Wilfrid Laurier University, and the University of Toronto describe a polypeptide sequence that serves as a “zip code” for delivery of proteins specifically to the outer surface of chloroplasts. Once the zip code sequence was defined, it was used to identify other, previously unknown proteins that also contained this sequence, and were also located on the chloroplast outer membrane. Collectively, these results define a new “targeting sequence” in plant cells required for the delivery of proteins to the chloroplast surface, and increase the number of proteins known to reside at that location. These results will be of greatest interest to other scientists interested in the fundamental mechanisms of chloroplast formation and function, activities that are essential for overall crop performance and yield.

Technical Abstract: Tail-anchored (TA) proteins are a unique class of integral membrane proteins that possess a single C-terminal transmembrane domain and target post-translationally to the specific organelles at which they function. While significant advances have been made in recent years in elucidating the mechanisms and molecular targeting signals involved in the proper sorting of TA proteins, particularly to the endoplasmic reticulum and mitochondria, relatively little is known about the targeting of TA proteins to the plastid outer envelope. Here we show that several known or predicted plastid TA outer envelope proteins (OEPs) in Arabidopsis possess a C-terminal RK/ST sequence motif that serves as a conserved element of their plastid targeting signal. Evidence for this conclusion comes primarily from experiments with OEP7.2, which is a member of the 7-kDa OEP family in Arabidopsis. We confirmed that OEP7.2 was localized to the plastid outer envelope and possesses a TA topology, and its C-terminal sequence (CTS), which includes the RK/ST motif, is essential for proper targeting to plastids. The CTS of OEP7.2 is functionally interchangeable with the CTSs of other TA OEPs that possess similar RK/ST motifs, but not with those that lack the motif. Further, a bioinformatics search based on a consensus sequence led to the identification of several new OEP TA proteins. Collectively, this study provides new insight to the mechanisms of TA protein sorting in plant cells, defines a new targeting signal for a subset of TA OEPs, and expands the number and repertoire of TA proteins at the plastid outer envelope.