reporter gene in tobacco protoplasts. Interestingly, this switch can be efficiently
turned off by far-red light (Muller et al. 2014). Muller et al. (2014) constructed a
light-inducible system by using an interdisciplinary SynBio approach embracing
mammalian and plant cell systems to typify a split transcription factor based on the
plant photoreceptor phytochrome B and one of its interacting factors (PIF6). This
system in tobacco protoplasts gave toggle switch-like characteristic which could be
turned ON when illuminated with red light (660 nm) and could be instantly returned
to the OFF state by successive illumination with far-red light (740 nm). They also
utilised this interplay for tuning auxin signalling networks in Nicotiana tabacum
protoplasts and for chemical-inducer free manufacture of therapeutic proteins in the
moss Physcomitrella patens (Muller et al. 2014). Similarly, Chatelle et al. (2018)
engineered a green light-responsive system based on the light-sensitive bacterial
transcription factor CarH and its related DNA operator sequence CarO from
Thermus thermophilus to regulate gene expression in A. thaliana protoplasts.
Smart plants harmonize with decision support systems by assisting farmers to
screen crop phosphorous (P) status by expressing in situ nontoxic marker gene.
Marker gene expression should commence specifically in reaction to P deficit and
well before P starvation restricts growth and development of the plant. Keeping this
in mind, Hammond et al. (2003) constructed transgenic Arabidopsis bearing a
marker gene (GUS) under the control of the promoter sequence for one of the
P-sensitive genes (SQD1) encoding synthesis of sulfolipids. Leaves of these plants
had GUS activity after P withdrawal, which was noticeable earlier than P starvation
could limit plant growth. Thus, this technology can allow meticulous execution of P
fertilization, preservation of natural resources, and improve sustainability
(Hammond et al. 2003). In addition, ABA receptors can be engineered to get
triggered by a synthetic molecule (that can be sprayed on a crop) which can facilitate
intervention to decrease water use in reaction to such inputs that plants themselves
cannot perceive like weather forecasts (Peterson et al. 2010).
Yeast Saccharomyces cerevisiae, growing at low pH, is favoured microbial host
producer and chassis cell for the production of economically important organic acids
(building blocks of a variety of products such as plastics, polymers and animal feed,
nylons, flavours and fragrances) (Sauer et al. 2008; Abbott et al. 2009; Williams
et al. 2017). Williams et al. (2017) recognized the S. cerevisiae WAR1 transcriptional regulator and PDR12 promoter as an organic acid biosensor that can be
utilized to perceive varying levels of para-hydroxybenzoic acid (PHBA) production
from the shikimate pathway as an input to express the output of green fluorescent
protein (GFP) expression. PHBA dependent GFP expression significantly increased,
by engineering positive feedback expression of the WAR1 from its target PDR12.
They used this biosensor in combination with a rational strain engineering approach
to precisely isolate PHBA-producing strains of S. cerevisiae even when they
corresponded to only 0.01% of a population. Fowler et al. (2010) constructed
intracellular sensors dependent on an RNA regulatory element known as a
riboswitch to detect the coenzyme B12 levels in E. coli cells. These probes sensitively detect their target using colorimetric, fluorescent or luminescent reporters. To
assess their utility in related cellular processes, the sensors were applied to scrutinize
15 Plant Synthetic Biology: A Paradigm Shift Targeting Stress Mitigation,. . .
453
turned off by far-red light (Muller et al. 2014). Muller et al. (2014) constructed a
light-inducible system by using an interdisciplinary SynBio approach embracing
mammalian and plant cell systems to typify a split transcription factor based on the
plant photoreceptor phytochrome B and one of its interacting factors (PIF6). This
system in tobacco protoplasts gave toggle switch-like characteristic which could be
turned ON when illuminated with red light (660 nm) and could be instantly returned
to the OFF state by successive illumination with far-red light (740 nm). They also
utilised this interplay for tuning auxin signalling networks in Nicotiana tabacum
protoplasts and for chemical-inducer free manufacture of therapeutic proteins in the
moss Physcomitrella patens (Muller et al. 2014). Similarly, Chatelle et al. (2018)
engineered a green light-responsive system based on the light-sensitive bacterial
transcription factor CarH and its related DNA operator sequence CarO from
Thermus thermophilus to regulate gene expression in A. thaliana protoplasts.
Smart plants harmonize with decision support systems by assisting farmers to
screen crop phosphorous (P) status by expressing in situ nontoxic marker gene.
Marker gene expression should commence specifically in reaction to P deficit and
well before P starvation restricts growth and development of the plant. Keeping this
in mind, Hammond et al. (2003) constructed transgenic Arabidopsis bearing a
marker gene (GUS) under the control of the promoter sequence for one of the
P-sensitive genes (SQD1) encoding synthesis of sulfolipids. Leaves of these plants
had GUS activity after P withdrawal, which was noticeable earlier than P starvation
could limit plant growth. Thus, this technology can allow meticulous execution of P
fertilization, preservation of natural resources, and improve sustainability
(Hammond et al. 2003). In addition, ABA receptors can be engineered to get
triggered by a synthetic molecule (that can be sprayed on a crop) which can facilitate
intervention to decrease water use in reaction to such inputs that plants themselves
cannot perceive like weather forecasts (Peterson et al. 2010).
Yeast Saccharomyces cerevisiae, growing at low pH, is favoured microbial host
producer and chassis cell for the production of economically important organic acids
(building blocks of a variety of products such as plastics, polymers and animal feed,
nylons, flavours and fragrances) (Sauer et al. 2008; Abbott et al. 2009; Williams
et al. 2017). Williams et al. (2017) recognized the S. cerevisiae WAR1 transcriptional regulator and PDR12 promoter as an organic acid biosensor that can be
utilized to perceive varying levels of para-hydroxybenzoic acid (PHBA) production
from the shikimate pathway as an input to express the output of green fluorescent
protein (GFP) expression. PHBA dependent GFP expression significantly increased,
by engineering positive feedback expression of the WAR1 from its target PDR12.
They used this biosensor in combination with a rational strain engineering approach
to precisely isolate PHBA-producing strains of S. cerevisiae even when they
corresponded to only 0.01% of a population. Fowler et al. (2010) constructed
intracellular sensors dependent on an RNA regulatory element known as a
riboswitch to detect the coenzyme B12 levels in E. coli cells. These probes sensitively detect their target using colorimetric, fluorescent or luminescent reporters. To
assess their utility in related cellular processes, the sensors were applied to scrutinize
15 Plant Synthetic Biology: A Paradigm Shift Targeting Stress Mitigation,. . .
453