Multiplex FAD2/FATB Editing Generates Ultra-High-Oleic, Low-Saturate Soybean With Increased Seed Fatty Acid Content

Oleic acid (18:1), saturated fatty acid (SFA), and polyunsaturated fatty acid (PUFA) levels are important traits for storage stability and edibility. In this study, we aimed to develop high-oleic soybean (Glycine max) by simultaneously targeting fatty acid desaturase 2 (FAD2) and fatty acyl-ACP thioesterase B (FATB) gene families using CRISPR/Cas9. Considering the paleopolyploid genome of soybean, multiple sgRNAs were designed to target GmFAD2-1, GmFAD2-2, and GmFATB genes expressed during seed development. Compared with targeting GmFAD2-1 alone (~83%), additional editing of GmFAD2-2B, GmFAD2-2C, and GmFATB1a increased the 18:1 fatty acid content to over 90%. Editing of GmFATB significantly reduced the SFA content by more than 40% compared with wild-type (WT). Reduced absolute SFA content was also observed in GmFAD2-only edited lines with decreased GmFATB expression. Notably, all evaluated high-oleic genotypes in the Williams82-background showed higher mean total fatty acid (TFA) content than the WT, both per unit seed mass and per seed. Correlation analysis of 805 individual seed profiles from Williams82-background lines further characterized the relationship between 18:1 fatty acid composition and TFA content per unit seed mass. Gene expression analysis revealed no consistent increase in triacylglycerol (TAG) synthesis genes, whereas the expression of sugar-dependent 1 (SDP1) was reduced. In contrast, genes involved in phosphatidic acid (PA) metabolism, including diacylglycerol kinase (DGK) and phospholipase D (PLD), were partially upregulated. These transcriptional changes support a hypothesis that altered lipid turnover may contribute to the higher TFA phenotype. Collectively, this study defines effective multiplex target combinations for ultra-high oleic, low-saturated soybean.