Aquaporin homologues in plants and mammals transport ammonia

Abstract
Using functional complementation and a yeast mutant deficient in ammonium (NH4 +) transport (Δmep1–3), three wheat (Triticum aestivum) TIP2 aquaporin homologues were isolated that restored the ability of the mutant to grow when 2 mM NH4 + was supplied as the sole nitrogen source. When expressed in Xenopus oocytes, TaTIP2;1 increased the uptake of NH4 + analogues methylammonium and formamide. Furthermore, expression of TaTIP2;1 increased acidification of the oocyte‐bathing medium containing NH4 + in accordance with NH3 diffusion through the aquaporin. Homology modeling of TaTIP2;1 in combination with site directed mutagenesis suggested a new subgroup of NH3‐transporting aquaporins here called aquaammoniaporins. Mammalian AQP8 sharing the aquaammoniaporin signature also complemented NH4 + transport deficiency in yeast.