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Lipid droplet-peroxisome connections in plants

Esnay Nicolas, John Dyer M., Robert Mullen T., Kent Chapman D., Kent Chapman
Contact 2020 v.3 no. pp. 1-14
ABC transporters, carboxylic ester hydrolases, droplets, eukaryotic cells, fatty acids, hydrolysis, lipophilicity, mammals, metabolism, peroxisomes, phenylalanine, proteome, seed germination, triacylglycerols, yeasts
Lipid droplets (LDs) are the principal subcellular sites for the storage of triacylglycerols (TAGs), and in plants, TAG degradation requires metabolism in peroxisomes. This metabolic cooperation includes TAG hydrolysis by the sugar-dependent 1 (SDP1) lipase located on the LD surface and the transfer of fatty acids into the peroxisome matrix by the peroxisomal membrane ABC transporter, PXA1. During seed germination this process fuels heterotrophic growth and involves the retromer-dependent formation of peroxisomal membrane extensions called ‘peroxules’ that interact with LDs. Similar changes in membrane architecture are observed also during interactions of peroxisomes and LDs in yeast and mammalian cells, despite differences in the molecular components required for their connections. Proteins directly involved in LD- peroxisome membrane contact site formation in plants have not yet been identified, but the connection between these two organelles is dependent upon PXA1, which contains a cytoplasmic exposed FFAT (phenylalanine – acidic tract) motif capable of interacting with vesicle-associated membrane protein (VAMP)-associated proteins (VAPs). The identification of several VAPs in plant LD proteomes suggests that a VAP-PXA1 connection might be part of functional tethering complex that connects these two organelles and allows for efficient transfer of lipophilic substrates from LDs to the peroxisome matrix in plant cells, similar to how VAPs participate in lipid transfer reactions between other subcellular compartments in eukaryotic systems.