Review: Ammonium as a signal for physiological and morphological responses ($)

Ammonium is one of the major forms in which nitrogen is assimilated. Besides being a nutrient, it also acts as signal that affects gene expression and root system architecture. Some ammonium-induced genes are also induced by low pH (ammonium acidifies the apoplast), whereas others are specifically induced by ammonium or its assimilation products (e.g., glutamine). Liu and von Wirén review the molecular components of ammonium signaling, which include the AMT ammonium transporters/transceptors. Although many components have been identified, many gaps in our understanding remain and are discussed. J Exp. Bot. 10.1093/jxb/erx086