Differential regulation of three functional ammonium transporter genes by nitrogen in root hairs and by light in leaves of tomato.
To elucidate the role of NH4+ transporters in N nutrition of tomato, two new NH4+ transporter genes were isolated from cDNA libraries of root hairs or leaves of tomato. While LeAMT1;2 is closely related to LeAMT1;1 (75.6% amino acid identity), LeAMT1;3 is more distantly related (62.8% identity) and possesses two short upstream open reading frames in the 5' end of the mRNA and a particularly short N-terminus of the protein as unique features. When expressed in yeast mutants defective in NH4+ uptake, all three genes complemented NH4+ uptake. In roots of hydroponically grown plants, transcript levels of LeAMT1;2 increased after NH4+ or NO3- supply, while LeAMT1;1 was induced by N deficiency coinciding with low glutamine concentrations, and LeAMT1;3 was not detected. In aeroponic culture, expression of LeAMT1;1 and LeAMT1;2 was higher in root hairs than in the remaining root fraction. Growth of plants at elevated CO2 slightly decreased expression of LeAMT1;2 and LeAMT1;3 in leaves, but strongly repressed transcript levels of chloroplast glutamine synthetase and photorespiratory serine hydroxymethyl-transferase. Expression of LeAMT1;2 and LeAMT1;3 showed a reciprocal diurnal regulation with highest transcript levels of LeAMT1;3 in darkness and highest levels of LeAMT1;2 after onset of light. These results indicate that in tomato at least two high-affinity NH4+ transporters, LeAMT1;1 and LeAMT1;2, are differentially regulated by N and contribute to root hair-mediated NH4+ acquisition from the rhizosphere. In leaves, the reciprocally expressed transporters LeAMT1;2 and LeAMT1;3 are supposed to play different roles in N metabolism, NH4+ uptake and/or NH3 retrieval during photorespiration.
von Wirén
N
N
Zentrum für Molekularbiologie der Pflanzen Tübingen (ZMBP), Tübingen.
Lauter
F R
FR
Ninnemann
O
O
Gillissen
B
B
Walch-Liu
P
P
Engels
C
C
Jost
W
W
Frommer
W B
WB
D000595:Amino Acid Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D027682:Cation Transport Proteins; D002940:Circadian Rhythm; D018506:Gene Expression Regulation, Plant; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism; D008027:Light; D018551:Solanum lycopersicum / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D010940:Plant Proteins; D018517:Plant Roots / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D016415:Sequence Alignment
D002352:Carrier Proteins; D027682:Cation Transport Proteins; D010940:Plant Proteins; D000644:Quaternary Ammonium Compounds; C088952:ammonium transporters, plant; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen