The Aspartate Kinase GmAK1 Controls Low-Phosphate Tolerance and Seed Oil Content in Soybean

Global soybean production is severely limited by phosphorus (P) deficiency, yet the underlying genetic factors linking low-phosphorus adaptation to seed composition traits have not been elucidated. In this study, transcriptomic analysis revealed that Aspartate Kinase 1 (GmAK1) expression is upregulated in leaves under phosphorus-deficient conditions, with the phosphorus-inefficient variety Tiefeng 3 (K5) exhibiting higher mRNA levels than the phosphorus-efficient variety Liaodou 13 (K4). Phenotypic analysis indicated that, under phosphorus-limiting conditions, overexpression (OE) lines exhibited lower total root length, surface area and volume compared to the wild-type control, whilst root phosphorus uptake efficiency was reduced and individual plant yield also decreased significantly. In contrast, the ak1s were able to maintain root volume and yield per plant during phosphorus deficiency, suggesting that GmAK1 overexpression alters key processes involved in root structural reorganisation and impairs the ability to efficiently absorb phosphorus. Furthermore, haplotype analysis of 581 soybean lines identified two major haplotypes, with Hap1 exhibiting higher seed oil content compared to Hap2. This association was functionally supported by the observation that OE seeds contained significantly lower oil content than the wild-type. In summary, our findings indicate that GmAK1 is a multifunctional regulatory factor and a promising candidate gene for breeding programs aimed at enhancing soybean resistance to phosphorus starvation and nutritional value.