Localized Expression of Arbuscular Mycorrhiza-Inducible Ammonium Transporters in Soybean

The majority of land plants acquire soil nutrients, such as phosphorus and nitrogen, not only through the root surface but also through arbuscular mycorrhizal (AM) fungi. Soybean is the most important leguminous crop in the world. We found 16 ammonium transporter genes in the soybean genome, five of which are AM inducible. Among them, promoter–reporter analysis indicated that the most abundantly transcribed gene, GmAMT4.1, showed specific expression in arbusculated cortical cells. Moreover, the GmAMT4.1–green fluorescent protein fusion was localized on the branch domain of periarbuscular membranes but not on the trunk region, indicating that active ammonium transfer occurs around the arbuscule branches.