The expression of genes encoding novel Sesame oleosin variants facilitates enhanced triacylglycerol accumulation in Arabidopsis leaves and seeds

Triacylglycerols (TAG), accumulate within lipid droplets (LD), predominantly surrounded by OLEOSINs (OLE), that protect TAG from hydrolysis. We tested the hypothesis that identifying and removing degradation signals from OLE would promote its abundance, preventing TAG degradation and enhancing TAG accumulation. We tested whether mutating potential ubiquitin-conjugation sites in a previously reported improved Sesamum indicum OLE (SiO) variant, o3-3 Cys-OLE (SiCO herein), would stabilize it and increase its lipogenic potential. SiCOv1 was created by replacing all five lysines in SiCO with arginines. Separately, six cysteine residues within SiCO were deleted to create SiCOv2. SiCOv1 and SiCOv2 mutations were combined to create SiCOv3. Transient expression of SiCOv3 in Nicotiana benthamiana increased TAG by two-fold relative to SiCO. Constitutive expression of SiCOv3 or SiCOv5, containing the five predominant TAG-increasing mutations from SiCOv3, in Arabidopsis along with mouse DGAT2 (mD) increased TAG accumulation by 54% in leaves and 13% in seeds compared with control lines coexpressing SiCO and mD. Lipid synthesis rates increased, consistent with an increase in lipid sink strength that sequesters newly synthesized TAG, thereby relieving the constitutive BADC-dependent inhibition of ACCase reported for WT Arabidopsis. These OLE variants represent novel factors for potentially increasing TAG accumulation in a variety of oil crops.