The jojoba lipid droplet protein LDAP1 facilitates the packaging of wax esters into lipid dropletsy

Jojoba (Simmondsia chinensis) is a desert shrub with an unusual capacity to store liquid wax esters (WEs) in its seeds instead of triacylglycerols (TAGs) like most oilseed crops. To examine the factors that are important for WE compartmentalization in jojoba, we reconstituted WE biosynthesis and packaging in the leaves of Nicotiana benthamiana. Using this system, we screened jojoba proteins for their ability to support lipid droplet (LD) formation. A specific LIPID DROPLET-ASSOCIATED PROTEIN (LDAP) isoform, ScLDAP1, was identified as a key factor in the efficient compartmentalization of WEs in plant cells. LDAP1 isoforms from other plants (e.g. Arabidopsis thaliana [AtLDAP1]) did not support WE partitioning from the endoplasmic reticulum into LDs, although both AtLDAP1 and ScLDAP1 were targeted specifically to LD monolayer surfaces. ScLDAP1-mediated selective, efficient WE partitioning was facilitated by an amphipathic α-helix near its C-terminus, and mutational analysis identified 1 amino acid residue within this helix that was both necessary and sufficient for proper WE packaging into cytoplasmic LDs. Taken together, our results provide a mechanistic link between the biosynthesis and storage of WEs in plant cells, and will inform future biotechnology strategies for the efficient packaging of various neutral lipid types as demonstrated here for WEs in transgenic seeds.