Functional characterization of an ammonium transporter gene from Lotus japonicus

NH4+ is the main product of symbiotic nitrogen fixation and the external co ncentration of combined nitrogen plays a key regulatory role in all the dif ferent step of plant-rhizobia interaction. We report the cloning and charac terization of the first member of the ammonium transporter family, LjAMT1:1 from a leguminous plant, Lotus japonicus. Sequence analysis reveals a clos e relationship to plant transporters of the AMT1 family. The wild type and two mutated versions of LjAMT1:1 were expressed and functionally characteri zed in yeast. LjAMT1:1 is transcribed in roots, leaves and nodules of L. ja ponicus plants grown under low nitrogen conditions. consistent with a role in uptake of NH4+ by the plant cells. (C) 2001 Elsevier Science B.V. All ri ghts reserved.