title: Knockdown of a rice stelar nitrate transporter alters long-distance translocation but not root influx.
abstract: Root nitrate uptake is well known to adjust to the plant's nitrogen demand for growth. Long-distance transport and/or root storage pools are thought to provide negative feedback signals regulating root uptake. We have characterized a vascular specific nitrate transporter belonging to the high-affinity Nitrate Transporter2 (NRT2) family, OsNRT2.3a, in rice (Oryza sativa ssp. japonica 'Nipponbare'). Localization analyses using protoplast expression, in planta promoter-β-glucuronidase assay, and in situ hybridization showed that OsNRT2.3a was located in the plasma membrane and mainly expressed in xylem parenchyma cells of the stele of nitrate-supplied roots. Knockdown expression of OsNRT2.3a by RNA interference (RNAi) had impaired xylem loading of nitrate and decreased plant growth at low (0.5 mm) nitrate supply. In comparison with the wild type, the RNAi lines contained both nitrate and total nitrogen significantly higher in the roots and lower in the shoots. The short-term [(15)N]NO(3)(-) influx (5 min) in entire roots and NO(3)(-) fluxes in root surfaces showed that the knockdown of OsNRT2.3a in comparison with the wild type did not affect nitrate uptake by roots. The RNAi plants showed no significant changes in the expression of some root nitrate transporters (OsNRT2.3b, OsNRT2.4, and OsNAR2.1), but transcripts for nia1 (nitrate reductase) had increased and OsNRT2.1 and OsNRT2.2 had decreased when the plants were supplied with nitrate. Taken together, the data demonstrate that OsNRT2.3a plays a key role in long-distance nitrate transport from root to shoot at low nitrate supply level in rice.
authors.affiliation: State Key Laboratory of Crop Genetics and Germplasm Enhancement and Key Laboratory of Plant Nutrition and Fertilization in Low-Middle Reaches of the Yangtze River, Ministry of Agriculture, Nanjing Agricultural University, Nanjing 210095, China.
authors.forename: Zhong
authors.initials: Z
authors.lastname: Tang
authors.forename: Xiaorong
authors.initials: X
authors.lastname: Fan
authors.forename: Qing
authors.initials: Q
authors.lastname: Li
authors.forename: Huimin
authors.initials: H
authors.lastname: Feng
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Miller
authors.forename: Qirong
authors.initials: Q
authors.lastname: Shen
authors.forename: Guohua
authors.initials: G
authors.lastname: Xu
mesh_terms: D027321:Anion Transport Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D055785:Gene Knockdown Techniques; D050901:Nitrate Reductase / Q000235:genetics / Q000378:metabolism; D000091285:Nitrate Transporters; D009566:Nitrates / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D009587:Nitrogen Isotopes; D012275:Oryza / Q000166:cytology / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D018520:Plant Shoots / Q000378:metabolism; D021381:Protein Transport; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D052584:Xylem / Q000378:metabolism*
chemical_list: D027321:Anion Transport Proteins; D000091285:Nitrate Transporters; D009566:Nitrates; D009573:Nitrites; D009587:Nitrogen Isotopes; D010940:Plant Proteins; D000644:Quaternary Ammonium Compounds; D012333:RNA, Messenger; D050901:Nitrate Reductase