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

TL;DR

This study identifies a spinach protein, SoNRT3, that improves plant growth under low-nitrogen conditions by enhancing nitrate uptake and root development.

Contribution

The novel contribution is the discovery of SoNRT3's role in low-nitrogen tolerance and its interaction with SoNRT2a in spinach.

Findings

SoNRT3 overexpression increases root growth and nitrate uptake under low-nitrate conditions.

SoNRT3 interacts with SoNRT2a to enhance low-nitrogen tolerance in spinach.

Transcriptome analysis suggests SoNRT3 promotes root development and nitrate assimilation.

Abstract

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 Arabidopsis thaliana, lines overexpressing SoNRT3 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. SoNRT3 silencing reduced taproot length, lateral root number, shoot/root biomass, and 15NO3− uptake in spinach grown under low-nitrate conditions. SoNRT3 partially compensated for 15NO3− uptake in atnrt2.1 and atnrt3.1 mutants. Transcriptome analysis showed that SoNRT3 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.

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