Genome engineering of disease susceptibility genes for enhancing resistance in plants

Introgression of disease resistance genes (R-genes) to fight against an array of phytopathogens takes several years using conventional breeding approaches. Pathogens develop mechanism(s) to escape plants immune system by evolving new strains/races, thus making them susceptible to disease. Conversely, disruption of host susceptibility factors (or S-genes) provides opportunities for resistance breeding in crops. S-genes are often exploited by phytopathogens to promote their growth and infection. Therefore, identification and targeting of disease susceptibility genes (S-genes) are gaining more attention for the acquisition of resistance in plants. Genome engineering of S-genes results in targeted, transgene-free gene modification through CRISPR-Cas-mediated technology and has been reported in several agriculturally important crops. In this review, we discuss the defense mechanism in plants against phytopathogens, tug of war between R-genes and S-genes, in silico techniques for identification of host-target (S-) genes and pathogen effector molecule(s), CRISPR-Cas-mediated S-gene engineering, its applications, challenges, and future prospects.