lignin in cell wall, thus shifted energy to produce more cellulose (Park et al. 2014).
They also engineered crops to express microbial cellulase enzymes (endoglucanase,
exoglucanase and beta-glucosidase) needed to convert the plant cellulose into
fermentable sugars in stovers (Park et al. 2011). SynBio can also offer a bioenergy
crop with cell walls rich in cellulose and hemicelluloses; but with more
bio-degradable lignin contents (Yang et al. 2013; Sticklen 2015). However, overaccumulation of sucrose can persuade negative feedback on the photosynthetic
mechanism, thus metabolic engineering also offers sink-side strategies on
transporting more carbon into a different sink, for example, sucrose transfer into
isomers like isomaltulose and trehalulose has been effectively engineered to augment total soluble sugar content in sugarcane (Wu and Birch 2007; Hamerli and
Birch 2011). In addition, bioenergy crops accumulating huge amounts of soluble
fermentable sugars should instantly process sugars post-harvest to avoid spoilage by
various opportunistic microbes.
Plants can also be exploited for the fabrication of lipases and phospholipases, the
enzymes used in the production of a nonpolluting and carbon-neutral fuel—
biodiesel. These plant-based enzymes can be either expressed directly in oil crops
or extracted in pure/crude form. Via advanced SynBio a crop, with synthetic genetic
circuits for lipid biosynthesis along with regulatory systems that can generate such
oil only in the non-edible or wasteful parts, can be designed (Ferry et al. 2012). With
efficient editing tools such as CRISPR/CAS9 (Puchta 2016), oil crops can be
engineered to suppress endogenous carbon sinks during the seed filling period.
Since the majority of the plant is composed of vegetative tissue, triacylglycerol
(TAG) production in vegetative tissue can be increased, for example, metabolically
engineering by stacking genes to increase TAG production in leaf tissue of Nicotiana
tabacum (Vanhercke et al. 2014) and in vegetative biomass of sugarcane (Zale et al.
2016). An increase in TAG levels in Arabidopsis leaf tissue has been achieved by
mutating genes like Trigalactosyldiacylglycerol1 (TGD1) and Sugar-Dependent1
(SPD1) to decrease fatty acid beta-oxidation (Fan et al. 2014). Synthetically
introduced tolerance traits in feedstock crops would push geographical/climatedependence borders of bioenergy plants, would boost the accessibility of renewable
products, and thus would increase the cost-competitiveness of biofuels (Shih et al.
2016). Algae with higher productivities than land plants and superior capability to
accumulate triacylglycerides (TAGs) are another appropriate host for bioengineering
related to biodiesel (Scott et al. 2010). The Commonwealth Scientific and Industrial
Research Organisation (CSIRO), Australia has synthetically engineered safflower
for yielding super high oleic acid-containing oils (SHOSO), which can replace some
petroleum-based raw materials used in bio-lubricants, biochemical and bioplastics
industries (Wood et al. 2018). In the current scenario, the concept of biorefinery in
which all raw materials are transformed into useful products, for example, sugar cane
processes utilising the bagasse and wood pulping processes utilizing even the bark,
are getting highlighted. Molecular farming offers potent implantation of low-cost
recombinant enzymes, like xylanase and oxidation/reduction enzymes such as
laccase and peroxidase (the imperative prerequisite in biorefineries) in plants
(Bussamra et al. 2015).
15 Plant Synthetic Biology: A Paradigm Shift Targeting Stress Mitigation,. . .
463
They also engineered crops to express microbial cellulase enzymes (endoglucanase,
exoglucanase and beta-glucosidase) needed to convert the plant cellulose into
fermentable sugars in stovers (Park et al. 2011). SynBio can also offer a bioenergy
crop with cell walls rich in cellulose and hemicelluloses; but with more
bio-degradable lignin contents (Yang et al. 2013; Sticklen 2015). However, overaccumulation of sucrose can persuade negative feedback on the photosynthetic
mechanism, thus metabolic engineering also offers sink-side strategies on
transporting more carbon into a different sink, for example, sucrose transfer into
isomers like isomaltulose and trehalulose has been effectively engineered to augment total soluble sugar content in sugarcane (Wu and Birch 2007; Hamerli and
Birch 2011). In addition, bioenergy crops accumulating huge amounts of soluble
fermentable sugars should instantly process sugars post-harvest to avoid spoilage by
various opportunistic microbes.
Plants can also be exploited for the fabrication of lipases and phospholipases, the
enzymes used in the production of a nonpolluting and carbon-neutral fuel—
biodiesel. These plant-based enzymes can be either expressed directly in oil crops
or extracted in pure/crude form. Via advanced SynBio a crop, with synthetic genetic
circuits for lipid biosynthesis along with regulatory systems that can generate such
oil only in the non-edible or wasteful parts, can be designed (Ferry et al. 2012). With
efficient editing tools such as CRISPR/CAS9 (Puchta 2016), oil crops can be
engineered to suppress endogenous carbon sinks during the seed filling period.
Since the majority of the plant is composed of vegetative tissue, triacylglycerol
(TAG) production in vegetative tissue can be increased, for example, metabolically
engineering by stacking genes to increase TAG production in leaf tissue of Nicotiana
tabacum (Vanhercke et al. 2014) and in vegetative biomass of sugarcane (Zale et al.
2016). An increase in TAG levels in Arabidopsis leaf tissue has been achieved by
mutating genes like Trigalactosyldiacylglycerol1 (TGD1) and Sugar-Dependent1
(SPD1) to decrease fatty acid beta-oxidation (Fan et al. 2014). Synthetically
introduced tolerance traits in feedstock crops would push geographical/climatedependence borders of bioenergy plants, would boost the accessibility of renewable
products, and thus would increase the cost-competitiveness of biofuels (Shih et al.
2016). Algae with higher productivities than land plants and superior capability to
accumulate triacylglycerides (TAGs) are another appropriate host for bioengineering
related to biodiesel (Scott et al. 2010). The Commonwealth Scientific and Industrial
Research Organisation (CSIRO), Australia has synthetically engineered safflower
for yielding super high oleic acid-containing oils (SHOSO), which can replace some
petroleum-based raw materials used in bio-lubricants, biochemical and bioplastics
industries (Wood et al. 2018). In the current scenario, the concept of biorefinery in
which all raw materials are transformed into useful products, for example, sugar cane
processes utilising the bagasse and wood pulping processes utilizing even the bark,
are getting highlighted. Molecular farming offers potent implantation of low-cost
recombinant enzymes, like xylanase and oxidation/reduction enzymes such as
laccase and peroxidase (the imperative prerequisite in biorefineries) in plants
(Bussamra et al. 2015).
15 Plant Synthetic Biology: A Paradigm Shift Targeting Stress Mitigation,. . .
463