metabolic cross talk between pathways and mechanisms to modulate the homeostasis of a given molecule which in excess can alter important developmental and
biochemical processes of the cell and the whole plant. Nevertheless, there has been
success in approaches that can increase the production of a metabolite by overexpressing genes that encode for key enzymes that directly influence the production
of the metabolite or by transcriptionally silencing genes encoding for enzymes that
use the precursor of the desired bioactive molecule into a different route and final
metabolic product. In most of the approaches described, stable transgenic plants are
generated by introducing an engineered DNA that contains the gene encoding for
the protein of interest to be produced (or the RNAi construct for the silencing of a
target gene), whose transcription is under the control of a ‘‘strong’’ regulatory
region or promoter region that makes sure the overexpression (or the silencing) is
efficient. In both cases, transformants are generated by Agrobacterium-mediated
transfer of the engineered DNA into wild-type plants, as previously described.
In the last decade a variety of studies targeting plant metabolic pathways have
been described, most of them with reasonable success in their attempt to improve
the synthesis of nutritional molecules such as carbohydrates, polyamines, fatty
acids, vitamins A and E, carotenoids, flavonoids, and mineral nutrients as iron and
zinc. Several examples of these are reviewed in Sharma and Sharma (2009). Here
we describe in detail the most recent ones.
An interesting recent example, using the overexpression approach in flax plants
(Linum usitatissimum), increases the levels of flavonoids. Zuk et al. (2012) generated transgenic flax plants overexpressing key genes of flavonoid pathway; the
resulting plants stably inherited and expressed the transgenes through generations
cultivated in field. Analyses of these plants showed an increase not only in the
production of flavonoid compounds such as kaempferol, but also in phenolic acids,
lignan, and fatty acids accumulation in oil from transgenic seeds. The authors
suggest that fatty acids accumulation is due to protection from oxidation during
fatty acid synthesis and seed maturation. Moreover, fibers of flax plants had an
increased level of catechine and acetovanillone. These results point to a potential
use of this type of approach as an important source of flavonoids, phenolic acids,
and lignan for biomedical application.
Producing oils with novel traits in crop plants has been a goal for diverse
research laboratories, which claim that oils with unusual fatty acids could replace
in the future petroleum-derived compounds and, in this way, promote green
chemistry. With these ideas in mind, Van Erp et al. (2011), engineered A. thaliana
plants with castor bean (Ricinus communis) fatty acid hydroxylase (RcFAH) and
phospholipid: diacylglycerol acyltransferase (RcPDAT). Plants which express only
RcFAH increased castor-like hydroxy fatty acid (HFA) content to only 17 % of the
total seed oil. Plants co-overexpressing both FAH12 and PDAT1A proteins
increased HFAs up to 30 % in seed oil.
A remarkable study by Naqvi et al. (2009), which combines the overexpression
of plant and bacterial genes in Z. Mays seeds, resulted in transgenic corn plants
with increased levels of vitamins. The experimental design used four cDNAs (two
of them from plants and two of them from bacteria) encoding enzymes in
15 Plants as Bioreactors for Human Health Nutrients
443
biochemical processes of the cell and the whole plant. Nevertheless, there has been
success in approaches that can increase the production of a metabolite by overexpressing genes that encode for key enzymes that directly influence the production
of the metabolite or by transcriptionally silencing genes encoding for enzymes that
use the precursor of the desired bioactive molecule into a different route and final
metabolic product. In most of the approaches described, stable transgenic plants are
generated by introducing an engineered DNA that contains the gene encoding for
the protein of interest to be produced (or the RNAi construct for the silencing of a
target gene), whose transcription is under the control of a ‘‘strong’’ regulatory
region or promoter region that makes sure the overexpression (or the silencing) is
efficient. In both cases, transformants are generated by Agrobacterium-mediated
transfer of the engineered DNA into wild-type plants, as previously described.
In the last decade a variety of studies targeting plant metabolic pathways have
been described, most of them with reasonable success in their attempt to improve
the synthesis of nutritional molecules such as carbohydrates, polyamines, fatty
acids, vitamins A and E, carotenoids, flavonoids, and mineral nutrients as iron and
zinc. Several examples of these are reviewed in Sharma and Sharma (2009). Here
we describe in detail the most recent ones.
An interesting recent example, using the overexpression approach in flax plants
(Linum usitatissimum), increases the levels of flavonoids. Zuk et al. (2012) generated transgenic flax plants overexpressing key genes of flavonoid pathway; the
resulting plants stably inherited and expressed the transgenes through generations
cultivated in field. Analyses of these plants showed an increase not only in the
production of flavonoid compounds such as kaempferol, but also in phenolic acids,
lignan, and fatty acids accumulation in oil from transgenic seeds. The authors
suggest that fatty acids accumulation is due to protection from oxidation during
fatty acid synthesis and seed maturation. Moreover, fibers of flax plants had an
increased level of catechine and acetovanillone. These results point to a potential
use of this type of approach as an important source of flavonoids, phenolic acids,
and lignan for biomedical application.
Producing oils with novel traits in crop plants has been a goal for diverse
research laboratories, which claim that oils with unusual fatty acids could replace
in the future petroleum-derived compounds and, in this way, promote green
chemistry. With these ideas in mind, Van Erp et al. (2011), engineered A. thaliana
plants with castor bean (Ricinus communis) fatty acid hydroxylase (RcFAH) and
phospholipid: diacylglycerol acyltransferase (RcPDAT). Plants which express only
RcFAH increased castor-like hydroxy fatty acid (HFA) content to only 17 % of the
total seed oil. Plants co-overexpressing both FAH12 and PDAT1A proteins
increased HFAs up to 30 % in seed oil.
A remarkable study by Naqvi et al. (2009), which combines the overexpression
of plant and bacterial genes in Z. Mays seeds, resulted in transgenic corn plants
with increased levels of vitamins. The experimental design used four cDNAs (two
of them from plants and two of them from bacteria) encoding enzymes in
15 Plants as Bioreactors for Human Health Nutrients
443