A. Quesada et al., PCR-IDENTIFICATION OF A NICOTIANA-PLUMBAGINIFOLIA CDNA HOMOLOGOUS TO THE HIGH-AFFINITY NITRATE TRANSPORTERS OF THE CRNA FAMILY, Plant molecular biology, 34(2), 1997, pp. 265-274
A family of high-affinity nitrate transporters has been identified in
Aspergillus nidulans and Chlamydomonas reinhardtii, and recently homol
ogues of this family have been cloned from a higher plant (barley). Ba
sed on six of the peptide sequences most strongly conserved between th
e barley and C. reinhardtii polypeptides, a set of degenerate primers
was designed to permit amplification of the corresponding genes from o
ther plant species. The utility of these primers was demonstrated by R
T-PCR with cDNA made from poly(A)(+) RNA from barley, C. reinhardtii a
nd Nicotiana plumbaginifolia. A PCR fragment amplified from N. plumbag
inifolia was used as probe to isolate a full-length cDNA clone which e
ncodes a protein, NRT2;1Np, that is closely related to the previously
isolated crnA homologue from barley. Genomic Southern blots indicated
that there are only 1 or 2 members of the Nrt2 gene family in N. plumb
aginifolia. Northern blotting showed that the Nrt2 transcripts are mos
t strongly expressed in roots. The effects of external treatments with
different N sources showed that the regulation of the Nrt2 gene(s) is
very similar to that reported for nitrate reductase and nitrite reduc
tase genes: their expression was strongly induced by nitrate but was r
epressed when reduced forms of N were supplied to the roots.