From Agronomy to Molecular Genetics and Proteomics in an Effort to Improve Nitrogen Use Efficiency in Crops - Crop Improvement: New Approaches and Modern Techniques - page 351

Table 11.2 List of transgenic effort towards improving N-use efficiency (NUE)
Gene Target plant Phenotype observed

Nrt1.1—high affinity nitrate
transporter

Arabidopsis Increase in constitutive nitrate

uptake but not induced

NR—nitrate reductase N. tabacum Three to four fold drop in NR

protein and activity, no change
in NR transcript

NiR—Nitrite reductase N. plumbaginifolia ,

Arabidopsis

NiR activity, no phenotypic
difference

GS2—chloroplastic glutamine
synthetase

N. tabacum Improved photorespiration capac-

ity, and increased resistance to
photo-oxidation

Fd-GOGAT—Fd dependent
glutamate synthase

N. tabacum Diurnal changes in NH3

assimilation

GS1—cytosolic glutamine
synthetase

N. tabacum, P. sativum Enhanced capacity to accumulate
nitrogen and enhanced growth
under N starvation higher
biomass and leaf proreins

NADH-GOGAT—NADH
dependent glutamate
synthase

O. sativa , N. tabacum Enhanced grain filling, increased
grain weight and higher total C
and N content, increased dry wt

GDH—glutamate
dehydrogenase

N. tabacum Increased biomass and dry weight

Dof1—transcription factor Arabidopsis Enhanced growth rate under

N-limited conditions, increase
in amino acid content

ANR1—MADS transcription
factor

Arabidopsis Lateral root induction and

elongation

no changes in total N, starch and productivity parameters were observed (Quillere
et al. 1994 ). The transgenics with NR double mutant Nia30 were not able to show
any detectable NR activity. While the when plant was transformed with the Nia2-
cDNA, a decreased in NR activity with enhanced levels of nitrate accumulation
was observed (Hansch et al. 2001 ). Transformed Nicotiana plumbaginifolia plants
that were constitutively expressing nitrate reductase (NR) showed a momentarily
delayed in drought-induced loss of NR activity, hence permitting speedy recov-
ery of N assimilation. Since NR enzyme is post-translationally controlled by phos-
phorylation and also with binding of 14-3-3 proteins, several attempts to reduce the
inhibitory effect on NR regulation have been made. 56 amino acids were deleted in
the amino terminal domain of NR that was known to impair this type of regulation
in Nicotiana plumbaginifolia (Provan et al. 2000 ). Over-expression of NR genes
from various plants have been worked on since past ten years (Lea et al. 2006 ), but
without any important outcome for the improvement in NUE.
In an effort for improving NUE, over expression of NiR genes were studied in
Arabidopsis and tobacco that though increased the NiR transcript levels but showed