Functional analysis of an Arabidopsis T-DNA "knockout" of the high-affinity NH4(+) transporter AtAMT1;1.
NH(4)(+) acquisition by plant roots is thought to involve members of the NH(4)(+) 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 NH(4)(+). 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 NH(4)(+) influx, we identified a homozygous T-DNA mutant with disrupted AtAMT1;1 activity. Contrary to expectation, high-affinity (13)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)NH(4)(+) influx in the mutant by 30% compared with wild-type plants, whereas low-affinity (13)NH(4)(+) influx (250 microM-10 mM NH(4)(+)) 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 NH(4)(+) and sucrose, the mutant grew poorly and died. Our results are the first in planta evidence that AtAMT1;1 is a root NH(4)(+) transporter and that redundancies within the AMT family may allow compensation for the loss of AtAMT1;1.
Kaiser
Brent N
BN
Department of Botany, University of British Columbia, Vancouver, Canada V6T 1Z4.
Rawat
Suman R
SR
Siddiqi
M Yaeesh
MY
Masle
Josette
J
Glass
Anthony D M
AD
D000645:Ammonium Sulfate / Q000494:pharmacology; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D001692:Biological Transport / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D027682:Cation Transport Proteins; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D020869:Gene Expression Profiling; D009154:Mutation; D009566:Nitrates / Q000494:pharmacology; D009584:Nitrogen / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000502:physiology; D018520:Plant Shoots / Q000187:drug effects / Q000502:physiology; D017680:Potassium Compounds / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D002352:Carrier Proteins; D027682:Cation Transport Proteins; D004269:DNA, Bacterial; D009566:Nitrates; D010940:Plant Proteins; D017680:Potassium Compounds; D012333:RNA, Messenger; C036483:T-DNA; C088952:ammonium transporters, plant; D009584:Nitrogen; C023844:potassium nitrate; D000645:Ammonium Sulfate