Bacterium-Mediated RNA Interference: Potential Application in Plant Protection

Abstract

RNAi has emerged as a promising tool for targeting agricultural pests and pathogens and could provide an environmentally friendly alternative to traditional means of control. However, the deployment of this technology is still limited by a lack of suitable exogenous- or externally applied delivery mechanisms. Numerous means of overcoming this limitation are being explored. One such method, bacterium-mediated RNA interference, or bmRNAi, has been explored in other systems and shows great potential for application to agriculture. Here, we review the current state of bmRNAi, examine the technical limitations and possible improvements, and discuss its potential applications in crop protection.

Keywords: RNA interference; bacterial-mediated RNAi; disease control; plant protection.

Figure 1

Schematic of processes and elements pertinent to bmRNAi crop protection A) hpRNA is transcribed from an expression construct within an endophytic bacterium. B) Bacteria applied by both invasive and non-traumatic administration systemically colonize the plant host via the vascular system. C) Bacteria secrete hpRNA into the extracellular milieu via lysis or secretion. D) Delivery bacteria present in the hosts’ extracellular matrix are internalized and colonize the cytoplasm. E) hpRNA present in the external environment are internalized via endocytosis. F) Bacteria secrete hpRNA into the cytoplasm via lysis or secretion. G) Bacteria are transferred between adjacent cells and into systemic circulation via xylem plates. H) hpRNA and siRNA produced locally are spread systemically via vascular transport I) Dicer-like proteins cleave hpRNA into 21–24 bp siRNA. J) Primary siRNA triggers secondary siRNA production via RNA-dependent RNA polymerases. K) hpRNA, siRNA and delivery bacteria are ingested by invertebrates feeding on treated plant tissue. L) hpRNA and siRNA are absorbed by fungi parasitizing the plant host. M) siRNA is loaded into RNA-induced silencing complexes (RISCs). N) Plant mRNA is transcribed and released into the cytosol. O) Viral mRNA and dsRNA are produced by viral replication and transcription. P) Cytosolic RISCs degrade and sequester complementary RNA, preventing translation and thereby silencing plant-expressed genes.