GWAS-based identification of GmKASII and its interaction with GmFATA1B reveals their role in soybean oil composition and accumulation.
Soybean (Glycine max L.) is a major oilseed crop worldwide, and its seed oil quality is largely determined by fatty acid composition. Although the enzymatic framework of plant fatty acid biosynthesis has been extensively characterized, the molecular mechanisms that regulate fatty acid partitioning and seed oil accumulation are not fully understood. In this study, genome-wide association analysis of soybean seed oil content identified GmKASII as a candidate gene underlying natural variation in seed oil accumulation, which was further supported by expression analysis and functional SNP characterization. Genetic manipulation of GmKASII significantly altered soybean seed oil accumulation and fatty acid composition. GmKASII overexpression increased seed oil content and promoted the accumulation of specific C18 fatty acids, including stearic acid (C18:0) and linoleic acid (C18:2), whereas gmkasII knockout reduced seed oil content and resulted in increased palmitic acid (C16:0) and decreased C18:0 levels. Protein-protein interaction assays, including yeast two-hybrid, luciferase complementation, and co-immunoprecipitation analyses, demonstrated that GmKASII physically interacts with acyl-ACP thioesterase GmFATA1B, suggesting a potential functional connection between fatty acid chain elongation and acyl-ACP hydrolysis pathways. Transient expression analysis in tobacco further suggested that co-expression of GmKASII and GmFATA1B influences fatty acid composition in a heterologous system. Collectively, these findings demonstrate that GmKASII plays an important role in regulating plastidial fatty acid flux and seed oil biosynthesis, and reveal a potential regulatory connection between fatty acid elongation and acyl-ACP release pathways in soybean.