NAT2/AAP1 as a Prototypical Example of the AAP Amino Acid Transporter Gene Family: From Protein Topology to Regulation of Gene Expression

Abstract

A genomic clone of NAT2 was isolated and sequenced. The 5' -flanking region contains several consensus recognition sites for putative transcription factors. I have now shown that NAT2 expression is nitrate and light inducible, but not circadian-regulated. Since the nitrate assimilatory enzymes are also induced by nitrate, the nitrate-inducible expression of NAT2 provides the first evidence connecting nitrate assimilation and amino acid transport. This observation supports the notion that NAT2 may be involved in phloem loading of newly synthesized amino acids in leaves. In addition, carbohydrate is able to enhance NAT2 expression in dark-adapted plants, suggesting the light induction may be mediated by production of carbohydrate, at least in part. These results provide new insight of environmental regulation of plant amino acid transporters.