Transgenic Applications in Wheat Improvement - Wheat Science and Trade - page 400

gene under control of the Ubi1 promoter had
greater water-use effi ciency and dry weight of
both shoots and roots than the nontransformed
parent under water-defi cit conditions in the
greenhouse (Sivamani et al., 2000a). In a series of
fi eld trials, these transgenic plants had greater
total biomass and grain yield at two of four dryland
locations and across all locations. The relative
water content of the leaves was correlated with
barley HVA1 expression levels.
The Arabidopsis DREB-1A gene encodes a
transcription factor that regulates genes involved
in drought, cold, and salt tolerance. Transgenic
wheat plants expressing the DREB-1A gene
under control of the Arabidopsis desiccation-
inducible rd29a gene promoter showed a 10-day
difference in the onset of wilting compared with
nontransformed plants, after water was withheld
in greenhouse experiments (Pellegrineschi et al.,
2004).
Xue et al. (2004) transformed wheat plants
with the Arabidopsis Na + /H + antiporter gene
ATNHX1 under control of the 35 S promoter.
The encoded vacuolar transport protein seques-
ters sodium ions in the vacuole. Plants that
expressed the transgene exhibited more effi cient
germination (84% vs. 68%) and produced about
1.5 times greater biomass under severe saline con-
ditions (100-150 mM NaCl) than nontransformed
plants in the greenhouse. The transgenic plants
also had 30% to 50% higher grain yield in the
fi eld under saline conditions than the nontrans-
formed parent (Xue et al., 2004).
Wheat plants containing a Vigna aconitifolia δ-
pyrroline-5-carboxylate synthetase gene under
control of the 35 S promoter overaccumulated
proline in their leaves at 12 times the control level
and could grow and set seed in 200 mM NaCl
(Sawahel and Hassan 2002). Expression of the
same gene under control of the stress-inducible
ABA-responsive element from the barley HVA22
gene promoter produced 2.5 times the amount of
proline in control plants at the booting stage, 14
days after withholding water (Vendruscolo et al.,
2007). Biochemical measurements in the stressed
plants led the authors to conclude that the accu-
mulated proline acts by protecting plant tissues

from oxidative damage rather than by mediating
osmotic adjustment.
Abebe et al. (2003) expressed the mannitol bio-
synthesis mtlD gene from E. coli under control of
the Ubi1 promoter in transgenic wheat and found
that the transgenic plants could better tolerate
100-150 mM salt and water-withholding treat-
ments. The increases in intracellular mannitol
levels measured in calli and in the fi fth leaf
of stressed transgenic plants were too small
to account for the protection by osmotic
adjustment.
One published report documents an attempt to
improve wheat frost tolerance by genetic transfor-
mation. Khanna and Daggard (2006) transformed
wheat with a fusion of the rice Act1 promoter to
the coding region from a fl ounder ( Pseudopleuro-
nectes americanus L.) antifreeze protein gene that
had been modifi ed to contain wheat-favored
codons. The secreted protein accumulated to
levels of 1.6% of leaf protein. An electrolyte
leakage assay showed that fl ag leaves were signifi -
cantly more resistant to frost damage than those
of the nontransformed parent at temperatures
between −1 and −7 ºC.

Other applications
Transformation technology has been used to
introduce completely new traits into wheat.
When the goal is herbicide resistance, the
selection gene and the gene of interest are
identical. Glyphosate-resistant or Roundup
Ready wheat plants were directly selected by
scientists at Monsanto Corporation after
Agrobacterium transfer of an Agrobacterium -
derived 5-enolpyruvylshikimate-3-phosphate
synthase ( EPSPS ) coding region under control
of various promoter and intron combinations
(Hu et al., 2003). Resistance to herbicides
with the active ingredient chloroacetanilide
(e.g., alachlor) was introduced into wheat by
genetic transformation with a maize glutathione
S-transferase gene under control of the Ubi1
promoter (Milligan et al., 2001). Not surpris-
ingly, many of the transformed plants from
experiments that have used Ubi1 :: bar as a