Application of Genome Editing for Improving Nematode Resistance in Plants: How far we have progressed?

Plant-parasitic nematodes (PPNs) cause immense yield loss in crop plants that ultimately affects the global crop productivity. The sedentary endoparasitic PPNs including root-knot and cyst nematodes induce feeding cells in their host plants that serves as the permanent nutrient sink for the nematodes and affect hosts’ own nutrition. During the last two decades nematode genome and transcriptome research has made considerable advancements that was translated into functional genomics studies including RNAi or host-induced gene silencing (HIGS)-based tactics deployment for obtaining nematode resistance. Nevertheless, HIGS strategy that involves targeting nematode effector genes are likely to fail because induced-silencing of effector genes (that interact with plant R genes) can result in the evolution of resistance-breaking nematode phenotypes. Recently, CRISPR-Cas9-based genome editing strategy was adopted to achieve host resistance against different phytopathogens including bacteria, fungi and virus. In those studies, researchers attempted to knock out the host susceptibility (S) genes to obtain resistance via loss of susceptibility. Since S genes are recessively inherited in the host plant, induced mutation of S genes can be durable and may confer broad-spectrum resistance. A number of S genes contributing plant susceptibility to nematodes have been characterized in different crop plants. A few of these S genes and a number of R genes were targeted for CRISPR-Cas9-based mutagenesis studies for improving nematode resistance or conferring nematode susceptibility in crop plants. However, CRISPR-Cas9-based genome editing were primarily deployed to investigate the molecular basis of plant–nematode interrelationship, rather than concentrated efforts towards targeting S genes. In this chapter, the applicability of this technique in plant–nematode infection model and its probable future outcome is being discussed in greater detail.