Heterologous Expression of Nitrate Assimilation Related-Protein DsNAR2.1/NRT3.1 Affects Uptake of Nitrate and Ammonium in Nitrogen-Starved Arabidopsis.

Nitrogen (N) is an essential macronutrient for plant growth. Plants absorb and utilize N mainly in the form of nitrate (NO3-) or ammonium (NH4+). In this study, the nitrate transporter DsNRT3.1 (also known as the nitrate assimilation-related protein DsNAR2.1) was characterized from Dianthus spiculifolius. A quantitative PCR (qPCR) analysis showed that the DsNRT3.1 expression was induced by NO3-. Under N-starvation conditions, the transformed Arabidopsis seedlings expressing DsNRT3.1 had longer roots and a greater fresh weight than the wild type. Subcellular localization showed that DsNRT3.1 was mainly localized to the plasma membrane in Arabidopsis root hair cells. Non-invasive micro-test (NMT) monitoring showed that the root hairs of N-starved transformed Arabidopsis seedlings had a stronger NO3- and NH4+ influx than the wild-type seedlings, using with NO3- or NH4+ as the sole N source; contrastingly, transformed seedlings only had a stronger NO3- influx when NO3- and NH4+ were present simultaneously. In addition, the qPCR analysis showed that the expression of AtNRT2 genes (AtNRT2.1-2.6), and particularly of AtNRT2.5, in the transformed Arabidopsis differed from that in the wild type. Overall, our results suggest that the heterologous expression of DsNRT3.1 affects seedlings' growth by enhancing the NO3- and NH4+ uptake in N-starved Arabidopsis. This may be related to the differential expression of AtNRT2 genes.