Molecular insights into the oleic acid accumulation in safflower

Abstract

Most of the Indian safflower (Carthamus tinctorius L.) varieties produce oil rich in linoleic acid (LA, ~75%) and low in oleic acid (OA, ~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.