A two-component high-affinity nitrate uptake system in barley

Authors

  • Yiping Tong,

    1. Crop Performance and Improvement Division, Harpenden, Hertfordshire, AL5 2JQ, UK
    2. The National Centre for Plant Gene Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
    Search for more papers by this author
  • Jing-Jiang Zhou,

    1. Biological Chemistry Division, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK
    Search for more papers by this author
  • Zhensheng Li,

    1. The National Centre for Plant Gene Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
    Search for more papers by this author
  • Anthony J. Miller

    Corresponding author
    1. Crop Performance and Improvement Division, Harpenden, Hertfordshire, AL5 2JQ, UK
      (fax +44 0 1582 763010; e-mail tony.miller@bbsrc.ac.uk).
    Search for more papers by this author

(fax +44 0 1582 763010; e-mail tony.miller@bbsrc.ac.uk).

Summary

The analysis of genome databases for many different plants has identified a group of genes that are related to one part of a two-component nitrate transport system found in algae. Earlier work using mutants and heterologous expression has shown that a high-affinity nitrate transport system from the unicellular green algae, Chlamydomonas reinhardtii required two gene products for function. One gene encoded a typical carrier-type structure with 12 putative trans-membrane (TM) domains and the other gene, nar2 encoded a much smaller protein that had only one TM domain. As both gene families occur in plants we investigated whether this transport model has more general relevance among plants. The screening for nitrate transporter activity was greatly helped by a novel assay using 15N-enriched nitrate uptake into Xenopus oocytes expressing the proteins. This assay enables many oocytes to be rapidly screened for nitrate transport activity. The functional activity of a barley nitrate transporter, HvNRT2.1, in oocytes required co-injection of a second mRNA. Although three very closely related nar2-like genes were cloned from barley, only one of these was able to give functional nitrate transport when co-injected into oocytes. The nitrate transport performed by this two-gene system was inhibited at more acidic external pH and by acidification of the cytoplasm. This specific requirement for two-gene products to give nitrate transport function has important implications for attempts to genetically manipulate this fundamental process in plants.

Ancillary