Agriculture Reference
In-Depth Information
Chapter 18
Transgenic Applications in
Wheat Improvement
Ann E. Blechl and Huw D. Jones
SUMMARY
decreases in their expression on traits of
transgenic wheat plants.
(5) Thus far, traits most frequently targeted
for change include herbicide resistance;
resistance to
Fusarium
, powdery mildew
(caused by
Blumeria graminis
f. sp.
tritici
),
and other fungi; drought and/or salt toler-
ance; seed protein and starch compositions
for enhanced end-use properties; and
mineral availability in seeds by accumula-
tion of phytase.
(6) The majority of transgenic wheat plants
containing new genes for high-molecular-
weight glutenin subunits (HMW-GS) and
bialaphos resistance show no effects on
nontargeted traits at either the molecular
level of transcription and metabolome or at
the whole-plant level as assessed by agro-
nomic performance in fi eld trials. Flours
made from seeds of these plants exhibit a
wide range of potentially useful mixing
properties.
(7) Current limitations to the application of
wheat transformation for commercial crop
improvement include an inability to control
the location, copy numbers, or linkage
relationships of transgene integration, lack
of predictability of the effects of genome
context on expression of newly integrated
genes, and societal opposition to the pres-
ence of genetically engineered wheat in the
food supply.
(1) The most reliable DNA introduction
methods that lead to fertile integrative
transformants of wheat are
Agrobacterium
and biolistics. These two methods result in
random integration of one or more copies
of the transgenes at one to a few locations
in the genome.
(2) Both durum (
Triticum durum
L.) and bread
wheat (
T. aestivum
L.) have been geneti-
cally transformed by biolistics and
Agro-
bacterium
methods. Reported effi ciencies
range from less than 0.2% to 70%, with
typical frequencies less than 5%.
(3)
Although many different cultivars of wheat
have been transformed, not all are amena-
ble to current methods, and transforma-
tion effi ciencies are genotype-dependent.
(4)
Genetic transformation has been used to
confi rm the identities of several agronomi-
cally important genes of wheat previously
isolated by map-based cloning. These
include genes that determine grain hard-
ness, three major vernalization genes, the
Q domestication gene, three leaf rust resis-
tance genes, and the
GPC-B1
gene that
infl uences grain protein, zinc, and iron
contents. In each case, the functions of
candidate gene sequences were verifi ed by
using transformation to test the effects of
their introduction or of increases or
