Plant Physiology Preview
Published on November 3, 2006; 10.1104/pp.106.091223
OPEN ACCESS ARTICLE
Received October 11, 2006
Accepted October 22, 2006
Dissection of the AtNRT2.1:AtNRT2.2 Inducible High-Affinity Nitrate Transporter Gene Cluster
Wenbin Li , Ye Wang , Mamoru Okamoto , Nigel M. Crawford , M. Yaeesh Siddiqi , and Anthony D.M. Glass *
Department of Botany, University of British Columbia, Vancouver, V6T1Z4, Canada
University of California, department of Biology 0116 9500 Gilman Drive La Jolla, CA 92093-0116, USA
* Corresponding author; email: aglass{at}interchange.ubc.ca.
Using a new Arabidopsis thaliana mutant (Atnrt2.1-nrt2.2) we confirm that concomitant disruption of NRT2.1 and NRT2.2 reduces inducible high-affinity nitrate influx (IHATS) by up to 80%, while the constitutive high-affinity influx (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%, while 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 A.thaliana. Disruption of NRT2.2 in Atnrt2.2 reduced IHATS by 19%, and this reduction was statistically significant only at 6h 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 inducible high-affinity nitrate influx. Nevertheless, when maintained on agar containing 0.25 mM KNO3 as 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.
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