were tested under field conditions. High yields of isomaltulose were obtained, up
to 81 % of total sugars in whole-cane juice from plants aged 13 months (Mudge
et al. 2013). Using promoters from sugarcane to drive expression preferentially in
the sugarcane stem, isomaltulose levels were consistent between stalks and stools
within a transgenic line and across consecutive vegetative field generations of
tested high-isomer lines. Importantly, these data represent the highest yields ever
achieved of value-added materials through plant metabolic engineering. The
sugarcane stem promoters are promising for strategies to achieve even higher
isomaltulose levels and for other applications in sugarcane molecular improvement. Silencing-resistant transgenes are critical for delivering the potential of these
promoters in practical sugarcane improvement. At the isomaltulose levels now
achieved in field-grown sugarcane, direct production of this disaccharide in plants
is feasible at a cost approaching that of sucrose, which should make the benefits of
isomaltulose affordable on a much wider scale.
5.6 Potentialities and Challenges of Sugarcane
as a Biofactory
Recently, sugarcane has become an important crop for food and energy production, and is emerging as a pivotal biofactory for high-value products. Its ability to
accumulate high levels of sucrose in its stems and its distinctive high yield make it
a unique crop, showing it to be the highest tonnage crop among cultivated plants.
Though breeding programs have focused on improving sugar content, an evolving
industry of biofuel and bio-based compounds such as biopolymers, pharmaceutical
proteins, and novel carbohydrates may require vast amounts of biomass and,
therefore, higher yields as well (Dal-Bianco et al. 2012).
Compared to other major crops, efforts to improve sugarcane are limited, as a
consequence of its narrow gene pool, complex genome for molecular breeding,
and the long breeding/selection cycle. These constraints, nonetheless, make sugarcane a good candidate for the application of molecular technologies. In recent
years, considerable progress has been made in understanding the sugarcane genome, creating transgenic plants with improved agronomic, industrial, or other
important traits, developing novel molecular markers, and understanding the
molecular aspects of sucrose biosynthesis, transport, and accumulation in greater
detail (Lakshmanan et al. 2005; Ming et al. 2006; Paterson et al. 2013). Accordingly, biotechnological routes for sugarcane improvement including technological
data available and the use of marker-assisted breeding, genome sequencing,
genetic engineering, and gene discovery for traits of interest are being addressed to
reach higher productivity goals and develop sustainable molecular pharming.
Although a plethora of advantages of crop plants as biofactories are well
documented (Ahmad et al. 2010; Becerra-Moreno et al. 2012; Jacobo-Velázquez
et al. 2011; Jenkins et al. 2011; Rigano et al. 2013) as they are renewable resources
of lower environmental impacts with balanced carbon emission, these systems also
5 Sugarcane as a Novel Biofactory: Potentialities and Challenges
139
to 81 % of total sugars in whole-cane juice from plants aged 13 months (Mudge
et al. 2013). Using promoters from sugarcane to drive expression preferentially in
the sugarcane stem, isomaltulose levels were consistent between stalks and stools
within a transgenic line and across consecutive vegetative field generations of
tested high-isomer lines. Importantly, these data represent the highest yields ever
achieved of value-added materials through plant metabolic engineering. The
sugarcane stem promoters are promising for strategies to achieve even higher
isomaltulose levels and for other applications in sugarcane molecular improvement. Silencing-resistant transgenes are critical for delivering the potential of these
promoters in practical sugarcane improvement. At the isomaltulose levels now
achieved in field-grown sugarcane, direct production of this disaccharide in plants
is feasible at a cost approaching that of sucrose, which should make the benefits of
isomaltulose affordable on a much wider scale.
5.6 Potentialities and Challenges of Sugarcane
as a Biofactory
Recently, sugarcane has become an important crop for food and energy production, and is emerging as a pivotal biofactory for high-value products. Its ability to
accumulate high levels of sucrose in its stems and its distinctive high yield make it
a unique crop, showing it to be the highest tonnage crop among cultivated plants.
Though breeding programs have focused on improving sugar content, an evolving
industry of biofuel and bio-based compounds such as biopolymers, pharmaceutical
proteins, and novel carbohydrates may require vast amounts of biomass and,
therefore, higher yields as well (Dal-Bianco et al. 2012).
Compared to other major crops, efforts to improve sugarcane are limited, as a
consequence of its narrow gene pool, complex genome for molecular breeding,
and the long breeding/selection cycle. These constraints, nonetheless, make sugarcane a good candidate for the application of molecular technologies. In recent
years, considerable progress has been made in understanding the sugarcane genome, creating transgenic plants with improved agronomic, industrial, or other
important traits, developing novel molecular markers, and understanding the
molecular aspects of sucrose biosynthesis, transport, and accumulation in greater
detail (Lakshmanan et al. 2005; Ming et al. 2006; Paterson et al. 2013). Accordingly, biotechnological routes for sugarcane improvement including technological
data available and the use of marker-assisted breeding, genome sequencing,
genetic engineering, and gene discovery for traits of interest are being addressed to
reach higher productivity goals and develop sustainable molecular pharming.
Although a plethora of advantages of crop plants as biofactories are well
documented (Ahmad et al. 2010; Becerra-Moreno et al. 2012; Jacobo-Velázquez
et al. 2011; Jenkins et al. 2011; Rigano et al. 2013) as they are renewable resources
of lower environmental impacts with balanced carbon emission, these systems also
5 Sugarcane as a Novel Biofactory: Potentialities and Challenges
139