Capacities and constraints of amino acid utilization in Arabidopsis

Summary•  Various amino acids, including both L‐ and D‐enantiomers, may be present in soils, and recent studies have indicated that plants may access such nitrogen (N) forms. Here, the capacity of Arabidopsis to utilize different L‐ and D‐amino acids is investigated and the constraints on this process are explored. •  Mutants defective in the lysine histidine transporter 1 (LHT1) and transgenic plants overexpressing LHT1 as well as plants expressing D‐amino acid‐metabolizing enzymes, were used in studies of uptake and growth on various N forms. •  Arabidopsis absorbed all tested N‐forms, but D‐enantiomers at lower rates than L‐forms. Several L‐ but no D‐forms were effective as N sources. Plants deficient in LHT1 displayed strong growth reductions and plants overexpressing LHT1 showed strong growth enhancement when N was supplied as amino acids, in particular when these were supplied at low concentrations. Several D‐ amino acids inhibited growth of wild‐type plants, while transgenic Arabidopsis ‐expressing genes encoding D‐amino acid‐metabolizing enzymes could efficiently utilize such compounds for growth. •  These results suggest that several amino acids, and in particular L‐Gln and L‐Asn, promote growth of Arabidopsis , and increased expression of specific amino acid transporters enhances growth on amino acids. The efficiency by which transgenic plants exploit D‐amino acids illustrates how plants can be engineered to utilize specific N sources otherwise inaccessible to them.