Involved in ammonium transport (By similarity). Required for arbuscular mycorrhizal (AM) symbiosis with AM fungi (e.g. Glomus versiforme and G.intraradices) in low nitrogen conditions (PubMed:25841038). Present on the periarbuscular membrane in cells containing arbuscules during arbuscular mycorrhizal (AM) symbiosis with AM fungi (e.g. Glomus versiforme). Mostly expressed in mycorrhizal roots (PubMed:25841038). Also observed in the cortex and endodermis of non-mycorrhizal roots (PubMed:25841038). Expressed in cortical cells containing arbuscules of mycorrhizal roots upon arbuscular mycorrhizal (AM) symbiosis with AM fungi (e.g. Glomus intraradices). Accumulates in roots during colonization by arbuscular mycorrhizal (AM) fungi (e.g. Glomus versiforme). Normal arbuscular mycorrhizal (AM) symbiosis with AM fungi (PubMed:25841038). Plants missing both PT4 and AMT2-3 fail to establish AM symbiosis with AM fungi in high nitrogen conditions, leading to premature arbuscule degeneration (PAD); these phenotypes are not suppressed in nitrogen-deprived conditions (PubMed:25841038). Belongs to the ammonia transporter channel (TC 1.A.11.2) family.