Lipid droplet-associated proteins (LDAPs) are required for the dynamic regulation of neutral lipid compartmentation in plant cells

Authors: GIDDA, SATINDER - University Of Guelph; PARK, SUNJUNG - University Of North Texas; PYC, MICHAL - University Of Guelph; Yurchenko, Olga; CAI, YINGQI - University Of North Texas; WU, PENG - University Of Toronto; ANDREWS, DAVID - University Of Toronto; CHAPMAN, KENT - University Of North Texas; Dyer, John; MULLEN, ROBERT - University Of Guelph

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2016
Publication Date: 2/19/2016
Publication URL: http://handle.nal.usda.gov/10113/62290
Citation: Gidda, S.K., Park, S., Pyc, M., Yurchenko, O., Cai, Y., Wu, P., Andrews, D.W., Chapman, K.D., Dyer, J.M., Mullen, R.T. 2016. Lipid droplet-associated proteins (LDAPs) are required for the dynamic regulation of neutral lipid compartmentation in plant cells. Plant Physiology. 170:2052-2071.

Interpretive Summary: Plant oils are important agricultural commodities that are commonly used for food and culinary purposes, and there is increasing demand for using these oils as feedstocks for biofuel production. Given that the demand for biofuels is far greater than what agriculture can typically deliver, there is great interest in understanding how plants produce and accumulate oils in order to develop knowledge-based approaches for elevating oil content. Most of our information regarding oil production in plants comes from studies of seeds, which can synthesize and accumulate large amounts of oil. All plant cell types, however, produce small amounts of oil. Thus, one potential avenue for increasing oil content is to enhance oil accumulation in leaves and stems (which have far greater biomass in comparison to seeds). In this study, scientists from the ARS lab in Maricopa, AZ, in collaboration with scientists at the University of North Texas and University of Guelph, characterized subcellular compartments called “lipid droplets” that store oil within all plant cells. While these organelles are highly abundant in plant seeds, they are dynamically regulated in vegetative cell types, showing strong diurnal changes in abundance that correlated with light and dark cycles. They also rapidly increased during heat or cold stress, revealing previously unappreciated roles for the organelles during abiotic stress responses. Characterization of proteins located on the surface of these organelles in plant leaves identified specific proteins required for both diurnal regulation and proliferation during stress responses. Furthermore, over-expression of these proteins elevated oil content in vegetative biomass. Taken together, these studies provide new insight to the function of these organelles in plants and will be of interest to scientists studying plant stress response, carbon/energy balance, and the engineering of bioenergy crops for enhanced biofuel production.

Technical Abstract: Eukaryotic cells compartmentalize neutral lipids into organelles called lipid droplets (LDs), and while much is known about the role of LDs in storing triacylglycerols (TAGs) in seeds, their biogenesis and function in non-seed tissues is poorly understood. Recently, we identified a class of plant-specific, LD-associated proteins (LDAPs) that are abundant components of LDs in non-seed cell types. Here, we characterized the three LDAPs in Arabidopsis thaliana to gain insight to their targeting, assembly and influence on LD function and dynamics. While all three LDAPs targeted with high specificity to the LD surface, truncation analysis of LDAP3 revealed that essentially the entire protein was required for LD localization. The association of LDAP3 with LDs was detergent-sensitive, but the protein bound with similar affinity to synthetic liposomes of various phospholipid compositions, suggesting that other factors contributed to targeting specificity. Investigation of LD dynamics in leaves revealed that LD abundance was modulated during the diurnal cycle, and characterization of LDAP mis-expression mutants indicated that all three LDAPs were important for this process. LD abundance was significantly increased during abiotic stress, and characterization of mutant lines revealed that LDAP3 was required for induction of LDs during cold temperature stress, while LDAP1 was required for heat stress. Furthermore, LDAP1 was required for proper neutral lipid compartmentalization and TAG mobilization during post-germinative growth. Taken together, these studies reveal that LDAPs are required for the maintenance and regulation of LDs in plant cells and perform non-redundant functions in various physiological contexts, including stress response and post-germinative growth.