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Biology and Biotechnology of Environmental Stress Tolerance in Plants, Volume 3

11.1 INTRODUCTION

Improvement of crop traits for designing the resistance against biotic and

abiotic stresses is a continual process worldwide from a long duration. Accli­

matizing advanced approaches and innovative tools is need of high priority

for sustainable and climate-smart food production and reduce effects greatest

threat of climate change (Lobell & Gourdji, 2012). Conventional breeding

was most effective way of crop trait improvement but is time-consuming (a

period of about 8–10 years), backbreaking and costly approach. Molecular

marker technology of restriction fragment length polymorphism (RFLP),

amplified fragment length polymorphism (AFLP), simple sequence repeats

(SSRs), single-nucleotide polymorphism (SNP) and diversity arrays tech­

nology (DArT) markers characterized plants under stress scenarios (Rao et

al., 2016). This tool may not produce stress-tolerant plants due to complex

inheritance and interactions of genotype and environment (Bhat et al.,

2016). Further, conventional breeding allows transmission of undesirable

genes alongside gene of Interest (GOI) to future progeny of plants. Because

of which multiple back-crossing events for a number of generations with

recipient is required to eradicate the unpredicted linked traits and to intro­

duce the desired trait from donor. Genetic engineering improved crops which

were exposed to any kind of biotic and abiotic stress by recombinant DNA

technology. But there are cost, timewasting, efficacies, social, and ethical

concerns, and further biosafety protocols limit approval for the genetically

modified (GM) crops (Prado et al., 2014; Raman, 2017). In GMOs, only

genes of Interest (GOI) are transferred to the recipient plant but there is non-

targeted integration. So, need of the hour is any new tool for improvement

of the plants subjected to stress which can withstand the upcoming scenarios

of global warming and climate changes. Beginning of various advanced

genome editing platforms involving molecular techniques has revolutionized

the area of agricultural crops. Sequence-specific nucleases (SSNs) recognize

precise and specific target DNA sites and introduce double-stranded breaks

(DSBs) at specific genomic loci in plants (Zhang et al., 2018; Costa et al.,

2017). CRISPR (clustered regularly interspaced short palindromic repeat)/

Cas (CRISPR-associated protein) system which is a new breeding technique

is simple, robust, prompt, highly efficient, low-cost, precise, adaptable, and

broadly acknowledged tool (Zhang et al., 2018). Genome editing takes only

4–6 years wherein precise modification of regulatory region of target genes

or target gene itself is done. CRISPR/Cas system consists of a complex

of Cas9 endonuclease and single guide RNA (sgRNA). The sgRNA gives