The OsAMT1.1 gene functions in ammonium uptake and ammonium–potassium homeostasis over low and high ammonium concentration ranges

Abstract

Rice (Oryza sativa) grown in paddy fields is an ammonium (NH4+)-preferring crop; however, its AMT-type NH4+ transporters that mediate root N acquisition have not been well characterized yet. In this study, we analyzed the expression pattern and physiological function of the OsAMT1.1 gene of the AMT1 subfamily in rice. OsAMT1.1 is located in the plasma membrane and is mainly expressed in the root epidermis, stele and mesophyll cells. Disruption of the OsAMT1.1 gene decreased the uptake of NH4+, and the growth of roots and shoots under both low NH4+ and high NH4+ conditions. OsAMT1.1 contributed to the short-term (5 min) 15NH4+ influx rate by approximately one-quarter, irrespective of the NH4+ concentration. Knockout of OsAMT1.1 significantly decreased the total N transport from roots to shoots under low NH4+ conditions. Moreover, compared with the wild type, the osamt1.1 mutant showed an increase in the potassium (K) absorption rate under high NH4+ conditions and a decrease under low NH4+ conditions. The mutants contained a significantly high concentration of K in both the roots and shoots at a limited K (0.1 mmol/L) supply when NH4+ was replete. Taken together, the results indicated that OsAMT1.1 significantly contributes to the NH4+ uptake under both low and high NH4+ conditions and plays an important role in N–K homeostasis in rice.