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

Gidda, Satinder K., Park, Sunjung, Pyc, Michal, Yurchenko, Olga, Cai, Yingqi, Wu, Peng, Andrews, David W., Chapman, Kent D., Dyer, John M., Mullen, Robert T.
Plant physiology 2016 v.170 no.4 pp. 2052-2071
Arabidopsis thaliana, biogenesis, cold stress, droplets, eukaryotic cells, germination, heat stress, leaves, mutants, organelles, phospholipids, plant growth, proteins, seeds, stress response, tissues, triacylglycerols
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.