Oleosin di-or tri-meric fusions with GFP undergo correct targeting and provide advantages for recombinant protein production

Plant oleosins are small proteins embedded within the phospholipid monolayer separating the triacylglycerol storage site of embryo-located oilbodies from the cytoplasm of oilseed cells. The potential of oleosins to act as carriers for recombinant proteins foreign to plant cells has been well established. Using this approach, the recombinant polypeptide is accumulated in oilbodies as a fusion with oleosin. DNA constructs having tandemly arranged oleosins followed by GFP or flanked by oleosins were used to transform Arabidopsis plants. In all cases the green fluorescence revealed that the fusion polypeptide had a native conformation and the recombinant proteins were correctly targeted to seed oilbodies. Mobilization of lipids was not retarded when using homo-dimer or -trimer oleosin fusions, since seed production, germination rates and seedling establishment were similar among all constructs, and comparable to wild-type Arabidopsis plants. Plant physiology and growth of recombinant lines were similar to wild-type plants. The construct specifying two oleosins flanking the GFP polypeptide revealed interesting properties regarding both the accumulation and the relative stability of the oilbody protein assembly. Although expression levels varied among transgenic lines, those transgenes accumulated significantly higher levels of fusion proteins as compared to previously reported values obtained by a single-oleosin configuration, reaching up to 2.3% of the total embryo proteins. These results shows that the expression cassettes comprising three oleosin molecules in frame to the GFP molecule or two oleosins flanking the GFP could be advantageous over the single-oleosin configuration for higher production and better commercialization of this plant biotechnological platform without jeopardizing plant vigour and physiology or oilbody stability.

Research highlights
► Here we report that multiple-oleosin configurations resulted in high productivity rates of the fusion transgenic proteins and correct compartmentalization.
► The transgenic oilbodies were very stable even under strong detergents. Our results showed that the physiology and yield of the transgenic plants is normal since seed production, germination rates, seedling establishment and plant growth were similar among all constructs and comparable to wild-type Arabidopsis.
► The “foreign” (GFP in this case) polypeptide took the correct conformation as this was evidenced under microscope and fluorescence directly in SDS gels.