From plastids to lipid droplets: molecular transporters orchestrating triacylglycerol accumulation in oilseed crops

SUMMARYOilseed crops are vital to global agriculture, industry, and nutrition. While the major enzymatic routes of triacylglycerol (TAG) formation are well established, the molecular mechanisms governing fatty acid (FA) and TAG trafficking across organelles remain only partially understood, and this gap constrains efforts to improve oil yield and composition. This review synthesizes recent advances on the lipid transporters mediating intracellular lipid movement and lipid droplet (LD) biogenesis in oilseeds. We briefly consider sugar transport as an upstream component of this network, providing carbon substrates for FA and TAG biosynthesis, before focusing on FA export from plastids, the cytosolic acyl-CoA pool that channels acyl groups toward the ER, and TAG deposition in LDs. We highlight emerging roles of fatty acid exporters (FAX), long-chain acyl-CoA synthetases (LACS), acyl-CoA-binding proteins (ACBPs), ATP-binding cassette (ABC) transporters, LD-associated proteins (LDAPs), LDAP-interacting proteins (LDIPs), seipins, and VAP27-1, as well as membrane contact sites (MCSs), particularly ER–plastid and ER_LD interfaces, as hubs for lipid exchange. Although many LD-associated proteins have been identified in plants, their specific functions and interactions remain unclear. Defining these transport routes will be essential for the metabolic engineering of oil yield and quality in oilseed crops.