Identification of a new class of lipid droplet-associated proteins in plants

Authors: HORN, PATRICK - University Of North Texas; JAMES, CHRISTOPHER - University Of North Texas; GIDDA, SATINDER - University Of Guelph; KILARU, ARUNA - East Tennessee State University; Dyer, John; MULLEN, ROBERT - University Of Guelph; OHLROGGE, JOHN - Michigan State University; CHAPMAN, KENT - University Of North Texas

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2013
Publication Date: 8/1/2013
Citation: Horn, P.J., James, C.N., Gidda, S.K., Kilaru, A., Dyer, J.M., Mullen, R.T., Ohlrogge, J.B., Chapman, K.D. 2013. Identification of a new class of lipid droplet-associated proteins in plants. Plant Physiology. 162:1926-1936.

Interpretive Summary: The seed oils of plants, also known as vegetable oils, are important for human nutrition and culinary purposes and the demand for these oils is increasing not only from increasing human population, but also from a burgeoning biofuels and renewable chemicals industry. In general, the demand for plant oils far outweighs what agriculture can typically deliver, and novel methods for dramatically increasing oil production in plants are widely sought. One avenue of research that is being aggressively pursued is to engineer plants to produce oil in the leaves and stems, in addition to seeds, since the majority of plant biomass is dominated by the former plant structures. Production of even modest amounts of oil in plant leaves and stems could significantly increase the amount of oil recovered from a given area of land. Rational engineering of plant biomass, however, requires a better understanding of the molecular factors involved in production, regulation, and turnover of oils in plant leaves. In a collaborative effort between scientists at the USDA-ARS lab in Maricopa Arizona, the University of Guelph, East Tennessee State University, Michigan State University, and the University of North Texas, a new class of proteins associated with oil production in plant leaves was identified. Somewhat surprisingly, these proteins were similar to proteins known to be involved in the production of rubber in certain rubber-accumulating plants such as Hevea brasiliensis and guayule. Taken together, these results define a larger class of proteins that may be important for producing both oils and rubber in the vegetative parts of plants, and may open new avenues of research for producing higher amounts of renewable fuels and chemicals in plants.

Technical Abstract: Lipid droplets in plants (also known as oil bodies, lipid bodies or oleosomes) are well characterized in seeds, and oleosins, the major proteins associated with their surface, were shown to be important for stabilizing lipid droplets during seed desiccation and rehydration. However, lipid droplets occur in essentially all plant cell types, many of which may not require oleosin-mediated stabilization. The proteins associated with the surface of non-seed lipid droplets, which are likely to influence the formation, stability and turnover of this compartment, remain to be elucidated. Here, we have combined lipidomic, proteomic and transcriptomic studies of avocado (Persea americana L.) mesocarp to identify two new lipid droplet-associated proteins, which we named lipid droplet-associated protein 1 and 2 (LDAP1 and LDAP2). These proteins are highly similar to each other and also to the small rubber particle proteins (SRPPs) that accumulate in rubber-producing plants. An Arabidopsis homolog to LDAP1 and LDAP2, At3g05500, was localized to the surface of lipid droplets after transient expression in tobacco cells that were induced to accumulate triacylglycerols. We propose that SRPP-like proteins are involved in the general process of binding and perhaps the stabilization of lipid-rich particles in the cytosol of plant cells and that the avocado and Arabidopsis protein members reveal a new aspect of cellular machinery that is involved in the packaging of triacylglycerols in plant tissues.