ABSTRACT
Nitrogen (N) is a critical factor for crop growth and yield. Improving N use efficiency (NUE) in agricultural systems is crucial for sustainable food production. However, the underlying regulation of N uptake and utilization in crops is not well known. Here, we identified OsSNAC1 (stress-responsive NAC 1) as an upstream regulator of OsNRT2.1 (nitrate transporter 2.1) in rice (Oryza sativa) by yeast 1-hybridization screening. OsSNAC1 was mainly expressed in roots and shoots and induced by N deficiency. We observed similar expression patterns of OsSNAC1, OsNRT2.1/2.2, and OsNRT1.1A/B in response to NO3- supply. Overexpression of OsSNAC1 resulted in increased concentrations of free NO3- in roots and shoots, as well as higher N uptake, higher NUE, and N use index (NUI) in rice plants, which conferred increased plant biomass and grain yield. On the contrary, mutations in OsSNAC1 resulted in decreased N uptake and lower NUI, which inhibited plant growth and yield. OsSNAC1 overexpression significantly upregulated OsNRT2.1/2.2 and OsNRT1.1A/B expression, while the mutation in OsSNAC1 significantly downregulated OsNRT2.1/2.2 and OsNRT1.1A/B expression. Y1H, transient co-expression, and ChIP assays showed OsSNAC1 directly binds to the upstream promoter regions of OsNRT2.1/2.2 and OsNRT1.1A/1.1B. In conclusion, we identified a NAC transcription factor in rice, OsSNAC1, with a positive role in regulating NO3- uptake through direct binding to the upstream promoter regions of OsNRT2.1/2.2 and OsNRT1.1A/1.1B and activating their expression. Our results provide a potential genetic approach for improving crop NUE in agriculture.
