Agriculture Reference
In-Depth Information
plants were reduced or absent. The same group
transformed wheat with the gene encoding the
WSMV coat protein. Although no coat protein
was detected, one of fi ve transgenic lines had
milder symptoms and a lower virus titer after
WSMV infection (Sivamani et al., 2002). Neither
of the lines that had shown greenhouse resistance
was resistant in 2 years of fi eld trials (Sharp et al.,
2002). In later investigations, some of these same
researchers found that the coat protein transgenes
had been silenced in the second- and third-
generation progeny of the transformants (Li et al.,
2005b).
Zhang et al. (2001) expressed a bacterial ribo-
nuclease III, which degrades double-stranded
RNA, under control of the
Ubi1
promoter. When
the transgenic wheat plants were infected with
Barley stripe mosaic virus
in a greenhouse, they
exhibited no infection symptoms and had reduced
virion accumulation compared to their nontrans-
formed parent (Zhang et al., 2001). Jiménez-
Martínez et al. (2004a) studied the interactions of
the bird cherry-oat aphid (
Rhopalosiphum padi
L.
)
vector with transgenic wheat plants express-
ing
Barley yellow dwarf virus
(BYDV) coat protein.
Compared with nontransformed plants, BYDV
virions were less effi ciently transferred by the
aphid after feeding on transgenic plants (Jiménez-
Martínez and Bosque-Pérez 2004), and BYDV-
infected transgenic plants were less attractive to
the aphids than BYDV-infected nontransformed
plants (Jiménez-Martínez et al., 2004b). The
virus titer was lower in transgenic plants than in
non-transgenic plants (Jiménez-Martínez et al.,
2004a).
The potential of various protease inhibitors to
control insect infestation in wheat has been tested
by genetic transformation. Altpeter et al. (1999)
expressed a barley trypsin inhibitor under control
of the
Ubi1
promoter. Seeds from some of their
transgenic plants accumulated the inhibitor to
levels of 1.1% of their protein. Early instar larvae
of the grain moth
Sitotroga cerealella
had reduced
survival and weights when fed transgenic seeds
compared to larvae fed seeds from nontransformed
wheat. Growth and survival of leaf-feeding
grasshoppers (
Melanoplus sanguinipes)
were not
different on transgenic and non-transgenic wheat
lines (Altpeter et al., 1999). Bi et al. (2006) pro-
duced three transgenic wheat lines expressing a
cowpea (
Vigna unguiculata
L.) trypsin inhibitor
gene under control of the 35
S
promoter. Seeds
from the transgenic plants had 44%-67% less
damage when exposed to grain moths for 3 months
(Bi et al., 2006). Hesler et al. (2005) found no
effects on the bird cherry-oat aphid when they
were fed transgenic wheat expressing a potato
(
Solanum tuberosum
L.) proteinase inhibitor II
gene under control of its own promoter.
Stoger et al. (1999a) used the maize
Ubi1
or a
rice phloem-specifi c sucrose synthase gene pro-
moter to express the coding region for a lectin
from snowdrop,
Galanthus nivalis
agglutinin
(GNA). The transgenic wheat accumulated GNA
to levels as high as 0.2% of leaf soluble protein.
Neonate nymphs of the grain aphid
Sitobion
avenae
that were allowed to colonize the trans-
genic plants for 16 days produced fewer offspring
than nymphs that colonized non-transgenic
plants. The transgenic plants had no effect on the
survival of either the grain aphid (Stoger et al.,
1999a) or of the cereal aphid
Metopolophium dirho-
dum
or of a cereal aphid biocontrol fungus
Pandora
neoaphidis
(Shah et al., 2005).
Vishnudasan et al. (2005) attempted to obtain
nematode resistance in durum wheat by express-
ing a potato serine proteinase inhibitor under
control of the rice
Act1
promoter. Ten-day-old
seedling progeny of heterozygous transgenic
plants inoculated with nematodes were taller and
had higher seed numbers and weights compared
with the non-transgenic controls. The increases
were well-correlated with the different levels of
proteinase inhibitor accumulated in the different
transgenic plants.
Applications to improve tolerance of
abiotic stress
Transgenic strategies to improve the drought and
salt tolerance of wheat by expressing either stress-
inducible gene regulators or increasing levels of
putative osmoprotectants show some promise.
Transgenic wheat expressing the barley
HVAI
