GmAux/IAA16 Exerts a Positive Regulatory Role in Enhancing Low-P Stress Tolerance in Plants

Background Soybean ( Glycine max (L.) Merr.), a globally significant crop, serves as a primary source of edible oil and protein. However, soil phosphorus (P) deficiency severely limits its productivity, reducing both yield and quality. Improving phosphorus-use efficiency to enhance low-P tolerance in soybean is therefore critical for sustainable cultivation. Results This study elucidates the molecular mechanism by which GmAux/IAA16 regulates root morphogenesis and coordinates low-phosphate responses in soybean. Bioinformatics analysis revealed that GmAux/IAA16 shares high sequence identity (92.43%) with its wild soybean ( Glycine soja L.) ortholog GsIAA16, and subcellular localization confirmed its nuclear-specific accumulation. Stable 35S:: GmAux/IAA16 transgenic tobacco lines, generated via Agrobacterium -mediated transformation, exhibited enhanced root development and maintained leaf physiological stability under phosphate deprivation. Physiological and biochemical analysis showed that the enzyme activities of IAAO (Indoleacetic acid oxidase), SOD (Superoxide dismutase), ACP (Acid phosphatase) and CAT (Catalase)in the root system of transgenic plants increased by 27.75%, 11.99%, 42.59% and 123.55% respectively, alongside elevated ATP levels, reduced MDA (Malondialdehyde) accumulation, and improved proline retention. Additionally, endogenous IAA (Indole-3-acetic acid), JA (Jasmonic acid), and SA (Salicylic acid) concentrations were significantly higher in both leaves and roots, suggesting a coordinated hormonal response that facilitates low-phosphate adaptation. Transcriptome data indicate that the overexpression of GmAux/IAA16 significantly reshapes the transcriptional map of tobacco roots under phosphorus stress. Conclusion The findings suggest that GmAux/IAA16 mediates low phosphorus tolerance through the cascade regulation of downstream phosphate-starvation response genes. This study provides novel insights into the regulatory role of the Aux/IAA gene family in soybean root development and phosphorus utilization efficiency. Furthermore, it identifies GmAux/IAA16 as a promising genetic target for molecular breeding of phosphorus-efficient soybean cultivars.