Secondary metabolites like carotenoids and their oxygen-containing derivatives,
xanthophylls have multifaceted roles in both plant and animal kingdom. In plants,
they mediate photosynthetic function, responses to biotic and abiotic signals, and
control plant architecture, while in animals they are allied with key concerns, like
vision and cardiovascular matters, efficient immune system, cognitive function and
antioxidant functioning (Wurtzel 2019). Thus, versatile carotenoids are one of the
important SynBio targets while taking into account ways to modify agriculture to
meet the needs of food security. Especially bioactivities of apocarotenoids, enzymatically cleaved carotenoids, are gaining attention as new toolkits that will transform SynBio applications in agriculture. They can potentially reconstruct plant
architecture by designing vigorous root systems promoting growth in poor quality
soils, inserting mycorrhizal colonization in presently non-mycorrhizal zones,
reforming plant-based chemical factories for synthesising de novo phytochemicals
that are easily harvestable from exudates or producing novel aromatic chemicals to
generate a defensive barrier against pathogens (Gao et al. 2018; Stauder et al. 2018).
SynBio can be utilised to design an adjustable biological circuit delivering a novel
strigolactone structure (Liu et al. 2018b) that functions in plants but is no longer
decipherable by unsafe rhizospheric biota and parasitic competitors. Wurtzel et al.
(2019) pointed out harnessing biological circuits to design synthetic carotenoids can
also generate stress-resilient plants to perk up light energy capturing efficiency and
photoprotection, or diverse plants (irrespective of their genetic background or plant
species) with novel carotenoids, or to create synthetic plant membranes with novel
carotenoid structures for improving mineral and oxygen uptake by roots or creating a
proficient blockade to plant pathogens (Wurtzel 2019). Synthetic production of plant
hormones like carotenoid-derived root exudates strigolactones can offer
opportunities to influence crop nutrient uptake, phytomorphology and reduce the
application of chemical fertilisers. By using the ‘bottom-up’ approach of SynBio,
isoprenoids including strigolactones were synthetically engineered and propagated
in yeast (Vickers 2016). Astaxanthin in conjunction with other ketocarotenoids, the
most expensive ingredient of salmon and trout feed (Moretti et al. 2006), can be
biologically extracted from only bacterium Paracoccus carotinifaciens, the alga
Haematococus pluvialis and the fungus Xanthophyllomyces dendrorhous (Ambati
et al. 2014). Thus attempts have been made to metabolically engineer the synthesis
of astaxanthin in crop plants like maize has been effectively engineered for high
b-carotene and zeaxanthin production in seed endosperm (Zhu et al. 2008). In
another maize line, lycopene e-cyclase was knocked down but phytoene synthase
gene was over-expressed (Farré et al. 2016) and these plants were crossed into a high
oil hybrid to yield maize seeds which can be fed to chicken as a source of astaxanthin
or can be processed for commercial astaxanthin (Breitenbach et al. 2016).
In the most commonly eaten fruits and vegetables, pigments anthocyanin,
guarding from wide range of diseases, are inadequate to confer optimal benefits.
Tissue-specific expression of an entire synthetic bacterial biosynthetic pathway
containing three Erwinia genes encoding phytoene synthase and desaturase along
with lycopene beta-cyclase under the regulation of golden tubers of potato (Solanum
tuberosum)-specific promoter resulted in many folds augment in carotenoids and
466
P. Singla
xanthophylls have multifaceted roles in both plant and animal kingdom. In plants,
they mediate photosynthetic function, responses to biotic and abiotic signals, and
control plant architecture, while in animals they are allied with key concerns, like
vision and cardiovascular matters, efficient immune system, cognitive function and
antioxidant functioning (Wurtzel 2019). Thus, versatile carotenoids are one of the
important SynBio targets while taking into account ways to modify agriculture to
meet the needs of food security. Especially bioactivities of apocarotenoids, enzymatically cleaved carotenoids, are gaining attention as new toolkits that will transform SynBio applications in agriculture. They can potentially reconstruct plant
architecture by designing vigorous root systems promoting growth in poor quality
soils, inserting mycorrhizal colonization in presently non-mycorrhizal zones,
reforming plant-based chemical factories for synthesising de novo phytochemicals
that are easily harvestable from exudates or producing novel aromatic chemicals to
generate a defensive barrier against pathogens (Gao et al. 2018; Stauder et al. 2018).
SynBio can be utilised to design an adjustable biological circuit delivering a novel
strigolactone structure (Liu et al. 2018b) that functions in plants but is no longer
decipherable by unsafe rhizospheric biota and parasitic competitors. Wurtzel et al.
(2019) pointed out harnessing biological circuits to design synthetic carotenoids can
also generate stress-resilient plants to perk up light energy capturing efficiency and
photoprotection, or diverse plants (irrespective of their genetic background or plant
species) with novel carotenoids, or to create synthetic plant membranes with novel
carotenoid structures for improving mineral and oxygen uptake by roots or creating a
proficient blockade to plant pathogens (Wurtzel 2019). Synthetic production of plant
hormones like carotenoid-derived root exudates strigolactones can offer
opportunities to influence crop nutrient uptake, phytomorphology and reduce the
application of chemical fertilisers. By using the ‘bottom-up’ approach of SynBio,
isoprenoids including strigolactones were synthetically engineered and propagated
in yeast (Vickers 2016). Astaxanthin in conjunction with other ketocarotenoids, the
most expensive ingredient of salmon and trout feed (Moretti et al. 2006), can be
biologically extracted from only bacterium Paracoccus carotinifaciens, the alga
Haematococus pluvialis and the fungus Xanthophyllomyces dendrorhous (Ambati
et al. 2014). Thus attempts have been made to metabolically engineer the synthesis
of astaxanthin in crop plants like maize has been effectively engineered for high
b-carotene and zeaxanthin production in seed endosperm (Zhu et al. 2008). In
another maize line, lycopene e-cyclase was knocked down but phytoene synthase
gene was over-expressed (Farré et al. 2016) and these plants were crossed into a high
oil hybrid to yield maize seeds which can be fed to chicken as a source of astaxanthin
or can be processed for commercial astaxanthin (Breitenbach et al. 2016).
In the most commonly eaten fruits and vegetables, pigments anthocyanin,
guarding from wide range of diseases, are inadequate to confer optimal benefits.
Tissue-specific expression of an entire synthetic bacterial biosynthetic pathway
containing three Erwinia genes encoding phytoene synthase and desaturase along
with lycopene beta-cyclase under the regulation of golden tubers of potato (Solanum
tuberosum)-specific promoter resulted in many folds augment in carotenoids and
466
P. Singla