Abstract

Ammonium transporters (AMTs) are responsible for ammonium absorption and utilization in plants. As a high-nitrogen-demand crop and a legume, soybean can also obtain ammonium from symbiotic root nodules in which nitrogen-fixing rhizobia convert atmospheric nitrogen (N2) into ammonium. Although increasing evidence implicates vital roles of ammonium transport in soybean, no systematic analyses of AMTs in soybean (named GmAMTs) or functional analyses of GmAMTs are available. In this study, we aimed to identify all GmAMT family genes and gain a better understanding of the characteristics ofGmAMTgenes in soybean. Here, due to the improved genome assembly and annotation of soybean, we tried to generate a phylogenetic tree of 16GmAMTsbased on new information. Consistent with reported data, GmAMT family members can be divided into two subfamilies ofGmAMT1(6 genes) andGmAMT2(10 genes). Interestingly, unlikeArabidopsis, which has only oneAMT2, soybean has substantially increased the number ofGmAMT2s, suggesting enhanced demand for ammonium transport. These genes were distributed on nine chromosomes, of whichGmAMT1.3, GmAMT1.4, andGmAMT1.5were three tandem repeat genes. The gene structures and conserved protein motifs of the GmAMT1 and GmAMT2 subfamilies were different. All the GmAMTs were membrane proteins with varying numbers of transmembrane domains ranging from 4 to 11. Promoter analysis found that theseGmAMTgenes have phytohormone-, circadian control-, and organ expression-relatedcis-elements in their promoters, and notably, there were nodulation-specific and nitrogen-responsive elements in the promoters of theGmAMT1andGmAMT2genes. Further expression data showed that these GmAMT family genes exhibited different spatiotemporal expression patterns across tissues and organs. In addition,GmAMT1.1, GmAMT1.2, GmAMT2.2, andGmAMT2.3were responsive to nitrogen treatment, whileGmAMT1.