Isolation and Expression of Gene Family for Ammonium Transporters Gene from Rice Plant

Abstract

The major form of nitrogen in paddy fields is NH₄⁺, requiring ammonium transporter (AMT) in roots. Also, in plant metabolisms AMTs are required in several processes. To characterize AMTs in rice, two cDNAs with high homology to MEP/AMT2-type AMTs, OsAMT2;1 and OsAMT3;1, were isolated. Expression of OsAMT2;1 in an ammonium-uptake defective yeast mutant showed that this gene encodes functional AMT. OsAMT2;1 was constitutively expressed in both roots and shoots irrespective of the supply of inorganic nitrogen to medium, whereas OsAMT3;1 expression was relatively weak. Database search with amino acid sequence of OsAMT2;1 showed that there are ten putative OsAMT genes, i.e. 3 each for OsAMT1, OsAMT2 and OsAMT3, respectively, and 1 for OsAMT4. Except OsAMT4;1, these genes were expressed in roots and leaf blades. NH₄⁺-inducible accumulation of OsAMT2;2 mRNA was seen in roots, while OsAMT3;3 was expressed following leaf senescence. Expression analyses are now in progress.