Spinach SoNRT3 Interacts with SoNRT2a to Improve Low-Nitrogen Tolerance via Nitrate Uptake and Root Growth.

High nitrogen use efficiency is crucial for enhancing spinach's tolerance to low nitrogen stress and minimizing nitrate accumulation. Here, we report that SoNRT3, a NAR2 family protein, modulates nitrate uptake and plant growth under low-nitrate conditions. SoNRT3 expression was induced by low nitrate availability in roots and prolonged nitrogen deficiency in shoots. Compared to wild-type , lines overexpressing exhibited higher root fresh weight, activities of nitrogen reduction/assimilation-related enzymes, tap root length, and total root diameter under low-nitrate (0.25 mM) conditions. silencing reduced taproot length, lateral root number, shoot/root biomass, and NO3- uptake in spinach grown under low-nitrate conditions. partially compensated for NO3- uptake in and mutants. Transcriptome analysis showed that may enhance nitrate uptake and root development by promoting the expression of high-affinity nitrate transporters, nitrogen assimilation, auxin signaling, and cell differentiation. Additionally, SoNRT3 can interact with a spinach NRT2 family protein (SoNRT2a), whose transcription level was also induced by low N and N deficiency. Together, this study clarifies the key roles and regulatory network of SoNRT3 in low-nitrate tolerance, which contributes to a novel understanding of nitrate utilization in spinach.