phenomenon was called cosuppression (Napoli et al. 1990). The previously
described studies led to the discovery of gene silencing by iRNA, since it was
elucidated that cosuppression was regulated by this mechanism; overexpression of
mRNA activates the machinery responsible for degrading the molecules of RNA
and prevents protein translation. The iRNA was adopted as a tool for the
manipulation of metabolic pathways suppressing the expression of target genes
(Fire et al. 1998) so far only single genes were used in the plant improvement;
these experiments and advances in the methods of transformation allow the
modification of multiple genes to control a metabolic pathway, showing better
results. This technology allows the modification of a single transgene and thus
itself controls the entire biosynthetic pathway. These proteins called transcription
factors (TFs), are used as regulators of gene expression through DNA–protein
interactions and provide a new tool for metabolic engineering, because of their
ability to control multiple steps in a synthesis pathway. Transcription factors
represent useful tools for manipulating the metabolism in specific organs or tissues
(Grotewold 2008). After it was discovered that epigenetics regulate gene expression by DNA methylation and histone acetylation multiple studies have demonstrated that these mechanisms play a key role in gene expression during
development of the plant, or under conditions of stress, generating an epigenetic
memory that allows plants to inherit these changes through mitosis and even by
meiosis (Chinnusamy and Zhu 2009). The analysis of biological systems with
bioinformatics allowed the prediction of the metabolism by mathematical models
and the use of databases, and thus the in silico design of strategies for metabolic
engineering. Analyses of the metabolic fluxes provide tools for theoretical prediction for the performance of specific metabolic pathways (Schwender 2008). In
recent years, tools have been developed that improve the understanding and
increase the metabolic engineering capacity, through the interaction of omics
sciences (genomic, metabolomic, and transcriptomic) increasing the chances of
success (Riechmann et al. 2000; Wiechert 2001).
15.4.2 Steps for the Modification of Metabolic Pathways
The process for the modification of a given metabolic pathway is divided into four
stages. First it is important to know and understand the metabolic pathway of
interest, the precursor compounds, the intermediates and enzymes that participate
their interaction with other routes of synthesis, control points and metabolic flux,
the transcription factors involved, the mechanisms of cellular transport, and tissues
where it develops the metabolic pathway. In the second stage is determined the
metabolic manipulation tools. Examples include the introduction of a gene that
express an enzyme that promotes the production of the metabolite of interest, the
introduction of two or more genes that regulate the multi-step route, gene silencing
mediated by iRNA, manipulation by expression of transcription factors, and
transformation systems stable or transient (Capell and Christou 2004). The third
15 Plants as Bioreactors for Human Health Nutrients
433
described studies led to the discovery of gene silencing by iRNA, since it was
elucidated that cosuppression was regulated by this mechanism; overexpression of
mRNA activates the machinery responsible for degrading the molecules of RNA
and prevents protein translation. The iRNA was adopted as a tool for the
manipulation of metabolic pathways suppressing the expression of target genes
(Fire et al. 1998) so far only single genes were used in the plant improvement;
these experiments and advances in the methods of transformation allow the
modification of multiple genes to control a metabolic pathway, showing better
results. This technology allows the modification of a single transgene and thus
itself controls the entire biosynthetic pathway. These proteins called transcription
factors (TFs), are used as regulators of gene expression through DNA–protein
interactions and provide a new tool for metabolic engineering, because of their
ability to control multiple steps in a synthesis pathway. Transcription factors
represent useful tools for manipulating the metabolism in specific organs or tissues
(Grotewold 2008). After it was discovered that epigenetics regulate gene expression by DNA methylation and histone acetylation multiple studies have demonstrated that these mechanisms play a key role in gene expression during
development of the plant, or under conditions of stress, generating an epigenetic
memory that allows plants to inherit these changes through mitosis and even by
meiosis (Chinnusamy and Zhu 2009). The analysis of biological systems with
bioinformatics allowed the prediction of the metabolism by mathematical models
and the use of databases, and thus the in silico design of strategies for metabolic
engineering. Analyses of the metabolic fluxes provide tools for theoretical prediction for the performance of specific metabolic pathways (Schwender 2008). In
recent years, tools have been developed that improve the understanding and
increase the metabolic engineering capacity, through the interaction of omics
sciences (genomic, metabolomic, and transcriptomic) increasing the chances of
success (Riechmann et al. 2000; Wiechert 2001).
15.4.2 Steps for the Modification of Metabolic Pathways
The process for the modification of a given metabolic pathway is divided into four
stages. First it is important to know and understand the metabolic pathway of
interest, the precursor compounds, the intermediates and enzymes that participate
their interaction with other routes of synthesis, control points and metabolic flux,
the transcription factors involved, the mechanisms of cellular transport, and tissues
where it develops the metabolic pathway. In the second stage is determined the
metabolic manipulation tools. Examples include the introduction of a gene that
express an enzyme that promotes the production of the metabolite of interest, the
introduction of two or more genes that regulate the multi-step route, gene silencing
mediated by iRNA, manipulation by expression of transcription factors, and
transformation systems stable or transient (Capell and Christou 2004). The third
15 Plants as Bioreactors for Human Health Nutrients
433