Most of the Indian safflower (Carthamus tinctorius L.) varieties produce oil rich in linoleic acid (LA, similar to 75%) and low in oleic acid (OA, similar to 15%). In the fatty acid biosynthetic pathway, the fatty acid desaturase 2 (FAD2) enzyme converts OA to LA. Safflower is reported to have 12-20 FAD2 genes. Gene expression analysis of four FAD2 genes during seed development in a high LA variety, PBNS-12, revealed high expression of FAD2-1 at 21 days after flowering (DAF), correlating with high LA accumulation. Fatty acid profiling of 448 Indian safflower germplasm accessions revealed four lines to have high (58%-77%) OA content, with NASF-39 having the highest OA content. Interestingly, all four high OA lines showed the same mutation in the FAD2-1 gene. The DNA sequence of FAD2-1 from the four high OA lines showed a deletion of C at the +606 position, resulting in a premature stop codon at the +733 position and a truncated protein of 244 amino acids. Hence, despite the high expression levels of FAD2-1 in NASF-39 at 18-21 DAF, it exhibited high OA (77%). The dysfunctional nature of the truncated FAD2-1 in NASF-39 was evident in molecular docking studies with 1-stearoyl-2-oleoyl phosphatidylcholine. We also sequenced FATB, a thioesterase responsible for releasing stearic acid from acyl carrier protein for further desaturation to oleic acid, where an A773G substitution was observed. This resulted in E258G substitution in NASF-39 FATB compared to that of PBNS-12. This probably made the acyl-binding pocket of NASF-39 FATB unstable, contributing to high OA accumulation. Thus, the outcomes of this study can help develop super and ultra-high oleic safflower varieties through various genetics and genomics approaches.

Foreign