Transgenic Applications in Wheat Improvement - Wheat Science and Trade - page 398

gene, vst1 or vst2 from grapevine and a pinosylvin
synthase gene from pine ( Pinus sylvestris L.), each
under control of the stress-inducible vst1 or vst2
promoters. The plants accumulated stilbene
derivatives that were similar to, but more hydro-
philic than, resveratrol or pinosylvin. The trans-
genic plants expressing the resveratrol synthase
genes showed 19%-27% reductions in symptoms
after infection with the biotrophic leaf rust
pathogen Puccinia triticina Eriks. and 42%-71%
reductions in symptoms after infection with
the facultative biotroph Septoria nodorum Berk
(Serazetdinova et al., 2005). In contrast, wheat
plants containing a pinosylvin synthase gene
controlled by a vst promoter were not protected
from either pathogen.
Clausen et al. (2000) obtained resistance to
stinking smut infection, caused by Tilletia caries
( DC.) Tul. & C. Tul. 1847 , by transforming two
Swiss wheat cultivars with the coding region of
a viral antifungal protein KP4, under control of
the Ubi1 promoter. One transformed line for
each cultivar showed a 30% decrease in symp-
toms in the greenhouse (Clausen et al., 2000) and
a 10% decrease in fi eld trials (Schlaich et al.,
2006).
Powdery mildew resistance has been the target
of several wheat transformation experiments. A
diagnostic test for resistance used in these reports
is measurement of the number and/or size of
colonies formed on detached leaves 5 to 7 days
after inoculation with the pathogen. By this cri-
terion, Bliffeld et al. (1999) found increased
resistance to powdery mildew in transgenic wheat
plants secreting a barley seed class II chitinase
controlled by the Ubi1 promoter. Investigators in
the same laboratory group expressed a secreted
barley RIP under control of the 35 S promoter
and an intron derived from the Rice tungro bacil-
liform virus (Bieri et al., 2000). Leaves of two of
the expressing lines had decreased mildew colony
formation of 40% and 80%. Expanding their
strategy in later experiments, the same group
expressed either the barnase RNAse under
control of the 35 S promoter and an intron, or a
barley seed chitinase and barley 1,3-β-glucanase
under control of the Ubi1 and Act1 promoters,
respectively. None of the transgenic plants with

the new constructs showed more resistance than
the original barley 35 S ::RIP lines (Bieri et al.,
2003). Combining the transgene loci for the three
barley proteins by crossing did not increase
protection.
Oldach et al. (2001) expressed either an Asper-
gillus giganteus antifungal protein or barley class
II chitinase with the Ubi1 promoter in transgenic
wheat. Leaves expressing the antifungal protein
had reductions of 40% to 50% in colony forma-
tion for both powdery mildew and leaf rust
inoculated with 80 to 100 spores per square cen-
timeter. The degree of protection was strongly
dependent on the inoculation dose. The barley
chitinase transgene conferred no protection
(Oldach et al., 2001). Zhao et al. (2006) reported
reduced symptoms in both greenhouse and fi eld
tests of second-generation transgenic wheat
plants expressing a tobacco β-1,3-glucanase con-
trolled by the 35 S promoter. Roy-Barman et al.
(2006) reported increases up to 50% in powdery
mildew resistance scored in the detached leaf
assay of second-generation transgenic plants
expressing a lipid transfer protein from Allium
under control of the Ubi1 promoter. Altpeter
et al. (2005) used the wheat pathogen-induced
GSTA1 promoter to express a wheat peroxidase
and oxalate oxidase in leaf epidermis. (These
proteins are normally found only in inner leaf
cells.) Leaves from the transgenic plants carrying
the peroxidase construct had less surface area
colonized by powdery mildew after infection
than those of the nontransformed parent. Expres-
sion of the oxalate oxidase was not protective.
The plants containing the peroxidase in epider-
mal cells responded to powdery mildew attack
more frequently than controls, with a hypersen-
sitive response comprising localized cell death
and production of hydrogen peroxide (Schweizer
2008).
Viral infections have been reduced in many
different plants by triggering cosuppression of
viral RNAs via overexpression of viral coat protein
or replicase genes (Beachy 1997). In wheat, this
strategy has had mixed success. Sivamani et al.
(2000b) expressed the replicase NIb of Wheat
streak mosaic virus (WSMV) and found that symp-
toms after WSMV infection of the transgenic