The role of nutrient uptake, signaling, and sensing for ammonium nutrition in plants
Quantitatively, nitrogen is the most important nutrient. In agriculture, nitrogen derives from mainly fertilizer application, (100-250 kg ha-1 a-1). Fertilizer production is costly, energy-consuming, and causes significant run-off with dramatic negative environmental and health impact. A better understanding of nitrogen acquisition in plants may help to engineer plants with improved nitrogen efficiency or optimize fertilization practice. Nutrient acquisition requires a fine balance between maximal nitrogen uptake and minimization of toxicity. The two dominant nitrogen forms are ammonium and nitrate. Ammonium can cause toxicity, thus requiring tight control over uptake and conversion efficacy inside cells. Recently the researchers identified the founding members of the ammonium transporter family (AMT/Mep/Rh). Plant AMTs helped identifying the long sought-for bacterial and human counterparts (Rhesus factors). Bacterial and fungal AMTs have function as transceptors, dual function proteins mediating transport and sensing. AMTs integrate information on ammonium levels, cellular energy supply, and availability of precursors for assimilation of ammonium. AMTs be further demonstrated form trimeric complexes and are subject to a novel allosteric regulatory mechanism involving the cytosolic C-terminus as a trans-regulatory domain. The unique trans-regulation in a complex of three similar/identical proteins is regulated by extracellular ammonium (and potentially other factors), and thus may be key to protecting against ammonium toxicity by fine-tuning ammonium accumulation. Given the role of the bacterial AMT counterparts in signaling, it is conceivable that plant AMTs are involved in sensing and signal integration as well. The objective of this project will be to unravel the regulatory mechanisms that control ammonium uptake, its integration with carbon- and energy status, and identify mechanisms that help protecting against ammonium toxicity. We have identified novel regulators for plant responses to ammonium exposure. And we’ve been studied the role of the regulatory AMT1 C-terminus in sensing and regulation by novel regulators. We’ve identified the phosphorylation sites on AMT1s and protein-protein interactions between CIPKs and AMT1 family in vitro and in vivo. cipks mutants shown more ammonium sensitivity phonotypes in primary root and shoot growth indicating the novel regulators play as negative regulators in plant under high ammonium toxicity.
