step is the evaluation of modified organisms. This involves measuring the copy
number of the gene of interest inserted, transcription, and metabolic profiles. At
this stage, there could appear some technical problems. For example, the lack of
expression of the gene of interest, the degradation or toxicity of an intermediary
product, and in many cases it presents the existence of a limiting factor. At this
stage the final product concentration is also evaluated (Dixon 2005).
15.4.3 Classification of Strategies for Modification
of Metabolic Pathways
The strategies for increasing the production of nutrients are classified into three
groups, the metabolic engineering initially used single genes insertion to obtain a
final product of interest; these initial experiments yielded the first generation of
transgenic crops and the discovery of the mechanism of cosuppression as negative
regulation allowed the development of iRNA strategy after having understood the
operation mechanism. Later, the strategy used in metabolic engineering was
transformation with multiples genes which include several methods for this object
such as crossing transgenic lines (Ma et al. 1995), sequential transformation (Qi
et al. 2004), cotransformation with standard binary vectors (Wu et al. 2005),
conventional vectors (Twyman et al. 2002), high-capacity binary vectors (BIBAC
or TAC) (Liu et al. 1999), assisted direct transfer (high-capacity transfer) (Wada
et al. 2009), artificial plant chromosome (Carlson et al. 2007), and operon systems
(De Cosa et al. 2001; Naqvi et al. 2010). The techniques mentioned above comprise the first strategy used by metabolic engineering. In recent years with the
appearance of TFs, it was possible to control entire metabolic pathways; these
master regulators have yielded better results in crop improvement. So it established a new strategy in the field of metabolic engineering which controls multiple
steps by a single transgene introduction (Yokotani et al. 2013). There are other
regulatory mechanisms at the epigenetic level that are attractive for metabolic
engineering in the potential applications for improving plants (Saze et al. 2003).
Below we show the classification of the strategies used by the metabolic engineering in plant breeding.
15.4.3.1 Modification of Metabolic Pathways
Metabolic engineering in plants involves the modification of endogenous pathways
to increase flux toward particular desirable molecules. In some cases the aim is to
enhance the production of a natural product, whereas in others it is to synthesize a
novel compound or molecule (Capell and Christou 2004). The manipulation of
single genes was first used in metabolic engineering to modify biosynthetic
434
L. A. Cruz-Ramírez et al.
number of the gene of interest inserted, transcription, and metabolic profiles. At
this stage, there could appear some technical problems. For example, the lack of
expression of the gene of interest, the degradation or toxicity of an intermediary
product, and in many cases it presents the existence of a limiting factor. At this
stage the final product concentration is also evaluated (Dixon 2005).
15.4.3 Classification of Strategies for Modification
of Metabolic Pathways
The strategies for increasing the production of nutrients are classified into three
groups, the metabolic engineering initially used single genes insertion to obtain a
final product of interest; these initial experiments yielded the first generation of
transgenic crops and the discovery of the mechanism of cosuppression as negative
regulation allowed the development of iRNA strategy after having understood the
operation mechanism. Later, the strategy used in metabolic engineering was
transformation with multiples genes which include several methods for this object
such as crossing transgenic lines (Ma et al. 1995), sequential transformation (Qi
et al. 2004), cotransformation with standard binary vectors (Wu et al. 2005),
conventional vectors (Twyman et al. 2002), high-capacity binary vectors (BIBAC
or TAC) (Liu et al. 1999), assisted direct transfer (high-capacity transfer) (Wada
et al. 2009), artificial plant chromosome (Carlson et al. 2007), and operon systems
(De Cosa et al. 2001; Naqvi et al. 2010). The techniques mentioned above comprise the first strategy used by metabolic engineering. In recent years with the
appearance of TFs, it was possible to control entire metabolic pathways; these
master regulators have yielded better results in crop improvement. So it established a new strategy in the field of metabolic engineering which controls multiple
steps by a single transgene introduction (Yokotani et al. 2013). There are other
regulatory mechanisms at the epigenetic level that are attractive for metabolic
engineering in the potential applications for improving plants (Saze et al. 2003).
Below we show the classification of the strategies used by the metabolic engineering in plant breeding.
15.4.3.1 Modification of Metabolic Pathways
Metabolic engineering in plants involves the modification of endogenous pathways
to increase flux toward particular desirable molecules. In some cases the aim is to
enhance the production of a natural product, whereas in others it is to synthesize a
novel compound or molecule (Capell and Christou 2004). The manipulation of
single genes was first used in metabolic engineering to modify biosynthetic
434
L. A. Cruz-Ramírez et al.