Food Biochemistry and Food Processing

3 Recent Advances 47

nine, and its first committed step is catalyzed by the
enzyme isoflavone synthase (EC 1.14.13.53) (Fig.
3.9). Jung et al. (2000) identified two soybean genes
encoding isoflavone synthase, IFS1/IFS2, and ex-
pressed these genes in A. thaliana, triggering the
synthesis of the isoflavonoid genistein. Although A.
thalianadoes not synthesize isoflavonoids, it does
have the substrate naringenin, which is an interme-
diate of the anthocyanin biosynthetic pathway.
Naringenin can then be converted to the isoflavonoid
genistein by a foreign isoflavone synthase. The soy
isoflavone synthase gene IFS1was cloned in the
plasmid pOY204 under the control of the 35S
CaMV promoter and transferred into A. thalianaby
Agrobacterium-mediated transformation. The intro-
duced ISF1gene expressed and produced active
isoflavone synthase in the transformed plant. The
amount of genistein produced was approximately
2ng/
g of fresh plant weight (Jung et al. 2000).

BIOENGINEERED ANIMALS

With the development of transgenic technology,
improvements in commercially important livestock
species have become possible by transferring genes
from related or unrelated species. Genetic improve-

ment through biotechnology can be achieved in one

generation, instead of the several generations re-

quired for traditional animal breeding methods. Al-

though several methods of gene transfer have been

developed, four methods are used today in the pro-

duction of most transgenic animals: nuclear transfer,

microinjection, viral vector infection, and embryon-

ic stem cell transfer. The nuclear transfer method

entails inserting the entire genetic material from the

nucleus of a donor cell into a mature unfertilized egg

whose nucleus has been removed. After that, the

embryo is transferred into a foster mother, where it

will develop into an animal that is genetically identi-

cal to the donor cell (Wolf et al. 2001). In micro-

injection, a segment of foreign DNA carrying one or

more genes is injected into the male pronucleus of a

fertilized egg. The egg needs to be in a single-cell

stage to ensure that all somatic cells in the animal

contain the transgene. The embryo is then trans-

ferred to the uterus of a surrogate mother (Wall

2002). In the retroviral infection technique, the gene

is transferred with the help of a viral vector. Ret-

roviruses are frequently used in the process of DNA

transfer due to their natural ability to infect cells

(Cabot et al. 2001). In the stem cell transfer tech-

nique, embryonic stem cells are collected from

Figure 3.9.Biosynthetic pathway for the soybean isoflavonoids: daidzein and genistein. (Adapted from Jung et al.
2000.)