ARS | Publication request: Hydrophobic-domain-dependent protein-protein interactions mediate the localization of GPAT enzymes to ER subdomains

Submitted to: Traffic
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 5, 2011
Publication Date: February 8, 2011
Citation: Gidda, S.K., Shockey, J.M., Rothstein, S.J., Dyer, J.M., Mullen, R.T. 2011. Hydrophobic-domain-dependent protein-protein interactions mediate the localization of GPAT enzymes to ER subdomains. Traffic. 12:452-472.

Interpretive Summary: Vegetable oils such as soybean and cottonseed oil are major agricultural commodities that are used for both food and industrial applications. Novel oils produced in new crops may also have special fatty acid compositions that are ideal for specific food or industrial end-uses. The value and utility of a plant oil, in general, is determined by the fatty acid composition, and thus, there is significant interest in modifying or optimizing the fatty acid composition of plant oils by using breeding or biotechnology approaches. However, our understanding of the molecular and genetic details that underpin oil production in plants is limited, and having this knowledge would enhance both breeding and biotechnology approaches. In collaboration with scientists at the University of Guelph, ARS scientists have gained significant insight to the cellular aspects of oil production in plant seeds, and showed that there are distinct regions within plant cells that are dedicated to oil production. This study describes the organization of these oil-producing “biofactories” and describes how they are put together and maintained. This information will be of immediate benefit to other scientists interested in understanding the basic aspects of oil production in plants, and will facilitate additional studies aimed at further increasing our understanding of this process in plants.

Technical Abstract: The endoplasmic reticulum (ER) is a dynamic network that consists of numerous regions or subdomains with discrete morphological features and functional properties, including those involved in protein and oil-body formation, anterograde transport of secretory proteins, the exchange of macromolecules with plastids and mitochondria, and lipid biosynthesis. While it is generally accepted that these subdomains differ in their protein and perhaps lipid compositions, a clear understanding of how they are established and maintained or how they are related to each other in terms of the overall organization of the ER has not been well established. Here we show that two tung (Vernicia fordii) membrane-bound glycerol-3-phosphate acyltransferase (GPAT) enzymes, GPAT8 and GPAT9, a newly-identified putative GPAT with homology to mammalian GPAT3, localize in tobacco suspension-cultured cells to the same ER subdomain that contains tung type 2 diacylglycerol acyltransferase (DGAT2), but is distinct from the ER subdomains containing DGAT1 or ER export sites. We also show using split-ubiquitin membrane yeast-two hybrid assays that GPAT8 interacts with itself, GPAT9 and DGAT2, but not with DGAT1. Furthermore, mutational analysis of GPAT8 indicates that the protein’s first predicted hydrophobic region, which contains an amphipathic helix-like motif known to be involved in the interactions and assembly of various other membrane-bound proteins, mediates ER subdomain localization. Taken together, these results suggest that the regulation and organization of ER subdomains involved in lipid biosynthesis in plant cells is mediated at least in part by higher-ordered, hydrophobic-domain-dependent homo- and hetero-oligomeric protein-protein interactions.