light-on/-off response (Mateo et al. 2015). A Shewanella oneidensis biosensor uses
outer membrane cytochrome complexes for concentration-dependent detection of
arabinose as electrochemical signals (Golitsch et al. 2013). Beside bioremediation,
another potential strategy to address land use problem is to engineer plants to grow
even in marginal land. Crop plants can be reverse engineered (Friedel et al. 2012),
using the sequences from plants like the aquatic and halophilic angiosperm Zostea
marina, to not only cultivate in non-arable land but also aid in its restoration (Olsen
et al. 2016).
Development in plant-based remediation and the designing of biosensors can
offer economical tools against ecological stresses. Metabolism of 2,4,6trinitrotoluene (TNT) in plants produces a nitro-radical which generates toxic superoxide by reacting with oxygen. Engineered plants, having a knockout of gene
encoding monodehydroascorbate reductase (generates the nitro-radical), exhibit
superior TNT tolerance (Johnston et al. 2015). In addition, regulating enzymatic
activity like phytochelatin synthase can also modify plant adaptation to toxic metals
like cadmium (Cahoon et al. 2015). Plants can also act as biosensors for scrutinizing
polluted sites (see details as sentinel plants in the section of biosensors). Plants
produce many dedicated metabolites as defence against attack from herbivores and
pests and to acclimatize to abiotic stresses. Engineering secondary metabolites by
escalating the flux in particular pathways and by understanding the regulation of
biosynthetic metabolons can be of incredible significance for developing resistant
crop varieties (Jirschitzka et al. 2013; Laursen et al. 2016). Important examples in
this regard are metabolic engineering of a cyanogenic glycoside—dhurrin
(Kristensen et al. 2005) and of raffinose family oligosaccharides in A. thaliana in
order to enhance resistance to biotic stress like Myzus persicae feeding (Cao et al.
2013; Barah and Bones 2015).
Setting up of synthetic promoters in conjunction with transcriptional tools to
substitute plant’s original promoters can enhance the development of stress-resistant
transgenic plants. Chen et al. (2010) proposed that WRKY transcription factors form
an intricate regulatory network that regulates gene expression in plant defence
responses against stress by acting as either transcription activators (WRKY18 and
WRKY60) or repressor (WRKY40). CRISPR–Cas9 is a genome editing tool
(editing—point mutation, deletions/insertions of genes or gene fragments; transcriptional regulation—CRISPRi, activation or repression, epigenomic modulations;
forward genetic screens—loss of function, knock down or activation mutants),
targeted to achieve improved biotic and abiotic stress tolerance in crop plants (Liu
et al. 2013a, b; Jain 2015; Ricroch et al. 2017). Wang et al. (2014) used TALEN and
CRISPR-Cas9 to incorporate targeted mutations in the three homoeoalleles that
encode MILDEW-RESISTANCE LOCUS (MLO) proteins in hexaploid bread
wheat to confer heritable broad-spectrum resistance to powdery mildew. The mutation of OsSWEET13 (one of the five SWEET genes) with CRISPR/Cas9 technology
specified the prerequisite of OsSWEET13 expression for the state of PthXo2dependent disease (bacterial blight) susceptibility of rice to γ-proteobacterium
Xanthomonas oryzae pv. Oryzae (Zhou et al. 2015). Li et al. (2016) used this
approach to bring in natural double amino acid substitutions (T102I + P106S
456
P. Singla
outer membrane cytochrome complexes for concentration-dependent detection of
arabinose as electrochemical signals (Golitsch et al. 2013). Beside bioremediation,
another potential strategy to address land use problem is to engineer plants to grow
even in marginal land. Crop plants can be reverse engineered (Friedel et al. 2012),
using the sequences from plants like the aquatic and halophilic angiosperm Zostea
marina, to not only cultivate in non-arable land but also aid in its restoration (Olsen
et al. 2016).
Development in plant-based remediation and the designing of biosensors can
offer economical tools against ecological stresses. Metabolism of 2,4,6trinitrotoluene (TNT) in plants produces a nitro-radical which generates toxic superoxide by reacting with oxygen. Engineered plants, having a knockout of gene
encoding monodehydroascorbate reductase (generates the nitro-radical), exhibit
superior TNT tolerance (Johnston et al. 2015). In addition, regulating enzymatic
activity like phytochelatin synthase can also modify plant adaptation to toxic metals
like cadmium (Cahoon et al. 2015). Plants can also act as biosensors for scrutinizing
polluted sites (see details as sentinel plants in the section of biosensors). Plants
produce many dedicated metabolites as defence against attack from herbivores and
pests and to acclimatize to abiotic stresses. Engineering secondary metabolites by
escalating the flux in particular pathways and by understanding the regulation of
biosynthetic metabolons can be of incredible significance for developing resistant
crop varieties (Jirschitzka et al. 2013; Laursen et al. 2016). Important examples in
this regard are metabolic engineering of a cyanogenic glycoside—dhurrin
(Kristensen et al. 2005) and of raffinose family oligosaccharides in A. thaliana in
order to enhance resistance to biotic stress like Myzus persicae feeding (Cao et al.
2013; Barah and Bones 2015).
Setting up of synthetic promoters in conjunction with transcriptional tools to
substitute plant’s original promoters can enhance the development of stress-resistant
transgenic plants. Chen et al. (2010) proposed that WRKY transcription factors form
an intricate regulatory network that regulates gene expression in plant defence
responses against stress by acting as either transcription activators (WRKY18 and
WRKY60) or repressor (WRKY40). CRISPR–Cas9 is a genome editing tool
(editing—point mutation, deletions/insertions of genes or gene fragments; transcriptional regulation—CRISPRi, activation or repression, epigenomic modulations;
forward genetic screens—loss of function, knock down or activation mutants),
targeted to achieve improved biotic and abiotic stress tolerance in crop plants (Liu
et al. 2013a, b; Jain 2015; Ricroch et al. 2017). Wang et al. (2014) used TALEN and
CRISPR-Cas9 to incorporate targeted mutations in the three homoeoalleles that
encode MILDEW-RESISTANCE LOCUS (MLO) proteins in hexaploid bread
wheat to confer heritable broad-spectrum resistance to powdery mildew. The mutation of OsSWEET13 (one of the five SWEET genes) with CRISPR/Cas9 technology
specified the prerequisite of OsSWEET13 expression for the state of PthXo2dependent disease (bacterial blight) susceptibility of rice to γ-proteobacterium
Xanthomonas oryzae pv. Oryzae (Zhou et al. 2015). Li et al. (2016) used this
approach to bring in natural double amino acid substitutions (T102I + P106S
456
P. Singla