Biotechnology of Fruit Quality - Fruit Ripening: Physiology, Signalling and Genomics - page 285

Therefore, enhancing a multigenic trait
became a focus of the second-generation
genetically engineered crops. These basic
strategies were used to accomplish this
objective. Because transcription factors
could control a number of downstream
genes, using them to engineer crops to
introduce complex polygenic traits such as
tolerance against abiotic stresses and
enhancing production of secondary
metabolites was another means of co-
expressing multiple genes. Some success
using such an approach has been achieved.
However, most metabolic pathways have
rate limiting step(s), and the simultaneous
expression of a number of genes may not
always help boost the intended trait(s).
Also, such a strategy may introduce a
negative override of metabolism and result
in lowering the desired attribute(s). None
the less, simultaneous introduction of
several genes helped develop high-level
E -carotene rice, designated Golden Rice
(Paine et al. , 2005). This study also
demonstrated that the source of gene(s)
plays a signifi cant role in increasing a
preferred molecule/nutrient; for instance,
the use of carotene desaturase from E.
uredovora resulted in a 23-fold increase in
total carotenoids in rice (Paine et al. , 2005).
It is implicit from such studies that a clear
understanding of the complex gene
expression and the process of production
of a desired metabolite is needed to enable
targeted expression of a transgene at a
desired stage of development of a specifi c
tissue. In this context and to solve such
complex hurdles, signifi cant new know-
ledge is desired to develop chimeric

promoters and accomplish targeted expres-
sion of the introduced genes at a specifi c
stage of fruit development.
In the near future, we see a need for
complementary interaction of practitioners
of biotechnology and conventional breed-
ing methods to accelerate the development
of novel fruit varieties with enhanced and
much desired attributes. Molecular genetic
tools such as QTL mapping, chromosome
walking, genome sequencing and bio-
informatics are powerful catalysts whose
use can help bring these approaches
together. Whereas the recombinant DNA
approach via transformation provides a
direct path to introducing new traits in
elite germplasm, more work and effort are
required to get rid of undesirable traits
introduced by a QTL-based approach.
The availability of molecular markers
associated with known traits should,
however, facilitate the use of this approach
to introduce desirable attributes in fruit
crops. We see a bright and exciting future
for precision-based engineering of quality
attributes in fruit crops.

Acknowledgements

A.K.H. and A.K.M. are supported by
USDA/NIFA 2010-65115-20374 and
USDA/NIFA 2012-67017-30159. R.A. is
supported by the Higher Education
Commission of Pakistan. Trade names or
commercial products mentioned in this
publication are only to provide specifi c
information and do not imply any recom-
mendation or endorsement by the authors.

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