Regulation of a putative high‐affinity nitrate transporter (Nrt2;1At) in roots ofArabidopsis thaliana

Abstract

Putative high-affinity nitrate (NO₃^–) transporter genes, designated Nrt2;1At and Nrt2;2At , were isolated from Arabidopsis thaliana by RT–PCR using degenerate primers. The genes shared 86% and 89% identity at the amino acid and nucleotide levels, respectively, while their proteins shared 30–73% identities with other eukaryotic highaffinity NO₃^– transporters. Both genes were induced by NO₃^–, but Nrt2;1At gene expression was not apparent in 2- and 5-day-old plants. By 10 days, and thereafter, Nrt2;1At gene expression in roots was substantially higher than for the Nrt2;2At gene. Root Nrt2;1At expression levels were strongly correlated with inducible high-affinity ¹³NO₃^– influx into intact roots under several treatment conditions. The use of inhibitors of N assimilation indicated that downregulation of Nrt2;1At expression was mediated by NH₄⁺, gln and other amino acids.