NRT2.1 mediates the reciprocal regulation of nitrate and NO/SNO in seedling leaves of Fraxinus mandshurica and Betula platyphylla

Abstract

Nitric oxide (NO) and S-nitrosothiol (SNO) are signal molecules and the products of nitrogen metabolism. Nitrate (NO₃⁻) is the main nitrogen source, and nitrate transporters (NRTs) are responsible for NO₃⁻ absorption or transport. However, the interactive effect between NO₃⁻/NRT and NO/SNO in tree plants remains ambiguous. In the present study, 25 mmol L⁻¹ NO₃⁻ and 1 mmol L⁻¹ NO donor sodium nitroprusside (SNP) treatment that was conducted for 24 h enhanced NO/SNO and NO₃⁻ metabolism, whereas 2.5 mmol L⁻¹ NO₃⁻ and 80 μmol L⁻¹ N6022 (a compound that increases SNO content) treatment reduced them in seedling leaves of Fraxinus mandshurica and Betula platyphylla. Among the nine NRT family members examined, the gene expression level of NRT2.1 had a greater response to NO/SNO and NO₃⁻ treatment in the seedling leaves of F. mandshurica and B. platyphylla. Meanwhile, FmNRT2.1 mediated NO and SNO production in seedling leaves of F. mandshurica using Agrobacterium-mediated transient transformation. These findings shed light on the reciprocal regulation between NO₃⁻ and NO/SNO in seedlings of F. mandshurica and B. platyphylla, and NRT2.1 may act as a key regulatory hub.