Dissection of the AtNRT2.1:AtNRT2.2 inducible high-affinity nitrate transporter gene cluster.
Using a new Arabidopsis (Arabidopsis thaliana) mutant (Atnrt2.1-nrt2.2) we confirm that concomitant disruption of NRT2.1 and NRT2.2 reduces inducible high-affinity transport system (IHATS) by up to 80%, whereas the constitutive high-affinity transport system (CHATS) was reduced by 30%. Nitrate influx via the low-affinity transport system (LATS) was unaffected. Shoot-to-root ratios were significantly reduced compared to wild-type plants, the major effect being upon shoot growth. In another mutant uniquely disrupted in NRT2.1 (Atnrt2.1), IHATS was reduced by up to 72%, whereas neither the CHATS nor the LATS fluxes were significantly reduced. Disruption of NRT2.1 in Atnrt2.1 caused a consistent and significant reduction of shoot-to-root ratios. IHATS influx and shoot-to-root ratios were restored to wild-type values when Atnrt2.1-nrt2.2 was transformed with a NRT2.1 cDNA isolated from Arabidopsis. Disruption of NRT2.2 in Atnrt2.2 reduced IHATS by 19% and this reduction was statistically significant only at 6 h after resupply of nitrate to nitrogen-deprived plants. Atnrt2.2 showed no significant reduction of CHATS, LATS, or shoot-to-root ratios. These results define NRT2.1 as the major contributor to IHATS. Nevertheless, when maintained on agar containing 0.25 mm KNO(3) as the sole nitrogen source, Atnrt2.1-nrt2.2 consistently exhibited greater stress and growth reduction than Atnrt2.1. Evidence from real-time PCR revealed that NRT2.2 transcript abundance was increased almost 3-fold in Atnrt2.1. These findings suggest that NRT2.2 normally makes only a small contribution to IHATS, but when NRT2.1 is lost, this contribution increases, resulting in a partial compensation.
Li
Wenbin
W
Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T1Z4.
Wang
Ye
Y
Okamoto
Mamoru
M
Crawford
Nigel M
NM
Siddiqi
M Yaeesh
MY
Glass
Anthony D M
AD
D000362:Agar; D027321:Anion Transport Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001692:Biological Transport / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D005810:Multigene Family; D016254:Mutagenesis, Insertional; D009154:Mutation; D009566:Nitrates / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018520:Plant Shoots / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism
D000362:Agar; D027321:Anion Transport Proteins; D029681:Arabidopsis Proteins; D009566:Nitrates; D012333:RNA, Messenger; C477335:NRT2.1 protein, Arabidopsis; C493954:NRT2.2 protein, Arabidopsis