Barley with the transgene for a heat-stable enzyme showed highly
variable levels of the enzyme, an anomalous distribution of expression in
the grain, and dramatically reduced weight of individual grains.
Barley (Hordeum vulgare L.), cultivar Golden Promise.
Gene for producing the heat stable enzyme beta-glucanase, derived from
bacteria. Two other genes were also part of the construct: a selectable
marker gene (bar) and a reporter gene (uidaA). So that the
genes would be expressed in all parts of the plant, they were fused with
a constitutive promoter (either maize pUbi-1 or synthetic pEmu).
Produce barley plants with enhanced ability to break down cell walls
during high-temperature malting. The introduced transgene would induce
barley to produce the heat-stable enzyme, beta-glucanase, which breaks down
cell wall components and does not degrade at high temperatures (over
Three plants contained all three genes (in multiple copies) and from these
eighteen homozygous lines of transgenic plants were propagated. These
were grown under field conditions and they stably expressed the target
enzyme, beta-glucanase, over three years.
Although all the transgenic barley plants showed similar DNA fragment
patterns (Southern blot analysis), they "produced significantly different
amounts of the recombinant enzyme," some having high levels, some low
levels, and others intermediate levels of expression.
The plants with high levels of beta-glucanase showed no expression of the
reporter gene (uidaA), although the gene was present, while in
plants with low levels of beta-glucanase, reporter gene expression was
"readily detected" (p. 10).
The weight of the grains of the transgenic barley plants in 1997 and
1998 was on average 31% and 41% less than unmanipulated barley plants,
although overall yield was comparable.
The active heat-stable enzyme was not present in the endosperm
(nutrient tissue) of the grain, where it "should" have been expressed,
but rather in the embryo of the grain, where it was not supposed to be
expressed. (Evidently the attached promoter did not function as intended,
perhaps due to "unsuitable insertion into chromatin" p. 10.)
The performance of high-enzyme-expressing transgenic lines and two
normal cultivars was compared under differing field conditions. There
was a "dramatic impact of different conditions on the field performance
of wild-type cultivars and the transgenic barley lines" (p. 4). Under
irrigated conditions in Idaho all types performed best; grain weight
and yield was, however, lower in the transgenic lines.
The authors state that "it is remarkable that plants with so similar
patterns in Southern blot analysis are not only different in the
expression levels of the analyzed intact beta-glucanase gene but also for
GUS [reporter gene (uidaA)] expression" (p. 10).
Horvath, H., L. G. Jensen, O. T. Wong, E. Kohl et al. (2001). "Stability
of Transgene Expression, Field Performance and Recombination Breeding
of Transformed Barley Lines," Theor Appl Genet vol. 102, pp. 1-11.
Washington State University; Plant Biology and Biochemistry Department,
Risø National Laboratory, Denmark.
USDA; Applied Phytologics, Sacramento, California; Washington Technology
Center (government/university/industry collaborative).
Not on the market as of 2008.
Copyright 2008 The Nature