RNAs - a new frontier in crop protection

Abstract

Small RNA (sRNA)-mediated RNA interference (RNAi) is a regulatory mechanism conserved in almost all eukaryotes. sRNAs play a critical role in host pathogen interactions either endogenously or by traveling between the interacting organisms and inducing 'cross-Kingdom RNAi' in the counterparty. Cross-kingdom RNAi is the mechanistic basis of host-induced gene silencing (HIGS), which relies on genetically expressing pathogen-gene targeting RNAs in crops, and has been successfully utilized against both microbial pathogens and pests. HIGS is limited by the need to produce genetically engineered crops. Recent studies have demonstrated that double-stranded RNAs and sRNAs can be efficiently taken up by many fungal pathogens, and induce gene silencing in fungal cells. This mechanism, termed 'environmental RNAi', allows direct application of pathogen-gene targeting RNAs onto crops to silence fungal virulence-related genes for plant protection. In this review, we will focus on how we can leverage cross-kingdom RNAi and environmental RNAi for crop disease control.

Figure 1:. RNAi-Based Plant Protection Strategies.

Two main strategies for RNAi based plant disease control exist, Host-Induced Gene Silencing (HIGS) and Spray-Induced Gene Silencing (HIGS). In HIGS approaches, the genetically engineered plant encodes pathogen targeting, double-stranded RNA in the nucleus, which is transported to the cytoplasm, where it can be processed into small RNAs by DCL proteins. These small RNAs can then be transported into pathogen or pests, via extracellular vesicles, where they target and silence pathogen mRNAs. Alternatively, they can operate within the plant cytoplasm to target and silence viral RNA. In SIGS approaches, pathogen targeting RNA, naked, packaged in organic nanoparticles, or packed in inorganic nanoparticles, is sprayed directly onto plant tissue. Next, it can be taken up by the pathogen/pest, where it targets and silences pathogen/pest genes. Alternatively, these sprayed RNAs can first be taken up by the plant, and then subsequently transported into the pest or pathogen.