Functional Analysis of an Arabidopsis T-DNA "Knockout" of the High-Affinity NH₄⁺ Transporter AtAMT1;1

• Published in: Plant physiology (Bethesda) 2002-11, Vol.130 (3), p.1263-1275
• Main Authors: Kaiser, Brent N., Suman R. Rawat, Siddiqi, M. Yaeesh, Josette Masle, Anthony D. M. Glass
• Format: Article
• Language: English
• Subjects: Ammonium Sulfate - pharmacology; Arabidopsis - drug effects; Arabidopsis - genetics; Arabidopsis - growth & development; Biological Transport - physiology; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cation Transport Proteins; Cell Biology and Signal Transduction; DNA; DNA, Bacterial - genetics; DNA, Bacterial - isolation & purification; Gene Expression Profiling; Gene expression regulation; Messenger RNA; Mutation; Nitrates; Nitrates - pharmacology; Nitrogen - metabolism; Nutrient solutions; Plant Proteins - genetics; Plant Proteins - metabolism; Plant roots; Plant Roots - drug effects; Plant Roots - physiology; Plant Shoots - drug effects; Plant Shoots - physiology; Plants; Polymerase chain reaction; Potassium Compounds - pharmacology; Quaternary ammonium compounds; Reverse Transcriptase Polymerase Chain Reaction; RNA; RNA, Messenger - genetics; RNA, Messenger - metabolism
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.102.010843

NH4 + acquisition by plant roots is thought to involve members of the NH4 + transporter family (AMT) found in plants, yeast, bacteria, and mammals. In Arabidopsis, there are six AMT genes of which AtAMT1;1 demonstrates the highest affinity for NH4 +. Ammonium influx into roots and AtAMT1;1 mRNA expression levels are highly correlated diurnally and when plant nitrogen (N) status is varied. To further investigate the involvement of AtAMT1;1 in high-affinity NH4 + influx, we identified a homozygous T-DNA mutant with disrupted AtAMT1;1 activity. Contrary to expectation, high-affinity ^{13}\text{NH}{}_{4}^{+}$ influx in the amt1;1:T-DNA mutant was similar to the wild type when grown with adequate N. Removal of N to increase AtAMT1;1 expression decreased high-affinity ^{13}\text{NH}{}_{4}^{+}$ influx in the mutant by 30% compared with wild-type plants, whereas low-affinity ^{13}\text{NH}{}_{4}^{+}$ influx (250 μM-10 mM NH4 +) exceeded that of wild-type plants. In these N-deprived plants, mRNA copy numbers of root AtAMT1;3 and AtAMT2;1 mRNA were significantly more increased in the mutant than in wild-type plants. Under most growth conditions, amt1;1:T-DNA plants were indistinguishable from the wild type, however, leaf morphology was altered. However, when grown with NH4 + and sucrose, the mutant grew poorly and died. Our results are the first in planta evidence that AtAMT1;1 is a root NH4 + transporter and that redundancies within the AMT family may allow compensation for the loss of AtAMT1;1.