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Constitutive expression of a putative high‐affinity nitrate transporter in Nicotiana plumbaginifolia : evidence for post‐transcriptional regulation by a reduced nitrogen source
Author(s) -
Fraisier Vincent,
Gojon Alain,
Tillard Pascal,
DanielVedele Françoise
Publication year - 2000
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.2000.00813.x
Subject(s) - transgene , biology , genetically modified crops , nicotiana , gene expression , gene , promoter , wild type , ammonium , nicotiana tabacum , coding region , microbiology and biotechnology , biochemistry , solanaceae , chemistry , mutant , organic chemistry
Summary The NpNRT2.1 gene encodes a putative inducible component of the high‐affinity nitrate (NO 3 – ) uptake system in Nicotiana plumbaginifolia . Here we report functional and physiological analyses of transgenic plants expressing the NpNRT2.1 coding sequence fused to the CaMV 35S or rolD promoters. Irrespective of the level of NO 3 – supplied, NO 3 – contents were found to be remarkably similar in wild‐type and transgenic plants. Under specific conditions (growth on 10 m m NO 3 – ), the steady‐state NpNRT2.1 mRNA level resulting from the deregulated transgene expression was accompanied by an increase in 15 NO 3 – influx measured in the low concentration range. This demonstrates for the first time that the NRT2.1 sequence codes a limiting element of the inducible high‐affinity transport system. Both 15 NO 3 – influx and mRNA levels decreased in the wild type after exposure to ammonium, in agreement with previous results from many species. Surprisingly, however, influx was also markedly decreased in transgenic plants, despite stable levels of transgene expression in independent transformants after ammonium addition. We conclude that the conditions associated with the supply of a reduced nitrogen source such as ammonium, or with the generation of a further downstream metabolite, probably exert a repressive effect on NO 3 – influx at both transcriptional and post‐transcriptional levels.