Overexpressing of OsAMT1-3, a High Affinity Ammonium Transporter Gene, Modifies Rice Growth and Carbon-Nitrogen Metabolic Status

Abstract

AMT1-3 encodes the high affinity NH4+ transporter in rice roots and is predominantly expressed under nitrogen starvation. In order to evaluate the effect of AMT1-3 gene on rice growth, nitrogen absorption and metabolism, we generated AMT1-3-overexpressing plants and analyzed the growth phenotype, yield, carbon and nitrogen metabolic status, and gene expression profiles. Although AMT1-3 mRNA accumulated in transgenic plants, these plants displayed significant decreases in growth when compared to the wild-type plants. The nitrogen uptake assay using a 15N tracer revealed poor nitrogen uptake ability in AMT1-3-overexpressing plants. We found significant decreases in AMT1-3-overexpressing plant leaf carbon and nitrogen content accompanied with a higher leaf C/N ratio. Significant changes in soluble proteins and carbohydrates were also observed in AMT1-3-overexpressing plants. In addition, metabolite profile analysis demonstrated significant changes in individual sugars, organic acids and free amino acids. Gene expression analysis revealed distinct expression patterns of genes that participate in carbon and nitrogen metabolism. Additionally, the correlation between the metabolites and gene expression patterns was consistent in AMT1-3-overexpressing plants under both low and high nitrogen growth conditions. Therefore, we hypothesized that the carbon and nitrogen metabolic imbalance caused by AMT1-3 overexpressing attributed to the poor growth and yield of transgenic plants.

Nitrogen Use Efficiency in Rice

“…Root-specific and nitrogen-derepressible expression for OsAMT1;3 may function as a nitrogen sensor [49,53]. Overexpression OsAMT1;3 displayed significant decreases in growth but with poor nitrogen uptake ability, accompanied with a higher leaf C/N ratio [54]. OsAMT2;1 showed constitutive expression in both roots and shoots, and OsAMT3;1 showed very weak expression in roots and shoots [46].…”

Expression of the Maize Dof1 Transcription Factor in Wheat and Sorghum

“…A number of transgenic approaches have been explored to enhance NUE in plants through the overexpression or knockout mutations of genes involved in nitrogen uptake, nitrate reduction, N assimilation, remobilization, recycling, amino acid biosynthesis, regulation of carbon/nitrogen metabolism, and signaling (Good et al, 2004; McAllister et al, 2012; Xu et al, 2012). Ectopic expression of Arabidopsis nitrogen transporter AtNRT1 .1 gene resulted in increased nitrate uptake in Arabidopsis (Liu et al, 1999), and the ammonium transporter, OsAMT1-1 , in rice enhanced ammonium uptake, which led to the increase in content of chlorophyll, starch, sugars, and grain yield in transgenic rice (Bao et al, 2015). In contrast, overexpression of the OsAMT1-3 induced carbon/nitrogen imbalances in transgenic rice, resulting in poor growth, and low yield (Bao et al, 2015).…”

“…Ectopic expression of Arabidopsis nitrogen transporter AtNRT1 .1 gene resulted in increased nitrate uptake in Arabidopsis (Liu et al, 1999), and the ammonium transporter, OsAMT1-1 , in rice enhanced ammonium uptake, which led to the increase in content of chlorophyll, starch, sugars, and grain yield in transgenic rice (Bao et al, 2015). In contrast, overexpression of the OsAMT1-3 induced carbon/nitrogen imbalances in transgenic rice, resulting in poor growth, and low yield (Bao et al, 2015). Moreover, manipulation of glutamine synthetase (GS)/glutamate synthase (GOGAT) cycle genes have been shown to enhance growth rate, yield, and biomass in tobacco, poplar, wheat, rice, and maize (Habash et al, 2001; Martin et al, 2006; Cai et al, 2009; Brauer et al, 2011; Molina-Rueda and Kirby, 2015; Seger et al, 2015).…”

Involvement of nitrogen in storage root growth and related gene expression in sweet potato (Ipomoea batatas)

“…Nitrate transporters NRT1 (low‐affinity nitrate transporter family) and NRT2 (high‐affinity nitrate transporter family) have been identified in the sensing and uptake of nitrate (Remans et al ., ; Lezhneva et al ., ; Mounier et al ., ; Sun & Zheng, ). Ammonium transporters (AMT) are effective in ammonium uptake (Ranathunge et al ., ; Bao et al ., ; Li et al ., ). Glutamine synthetase (GS) and NR (nitrate reductase) are key regulators of N metabolism and sensing (Yanagisawa, ; Avila‐Ospina et al ., ; Kalimuthu et al ., ).…”