Protecting Australian grain crops against fungal disease requires the development of safe and sustainable pesticides suited to modern practices and markets. This project aims to develop non-toxic RNA-based biopesticides for the control of rust pathogens of major cereal crops through RNA interference (RNAi). We have shown that exogenous double-stranded RNA (dsRNA) sprays can effectively prevent and cure disease caused by the myrtle rust pathogen that threatens many of Australia’s iconic and indigenous Myrtaceae species, including genera such as Eucalyptus, Psidium, and Syzygium (Degnan et al., 2022, 2023). However, we have found dsRNA to be much less effective in controlling stem rust and leaf rust of wheat.
It has been reported that ~20% of mRNAs are graft-transmissible in plants, and that specific transfer-RNA (tRNA) motifs within transcripts confer their graft-transmissibility (Zhang et al., 2016). Furthermore, we have shown that adding graft-transmissible tRNA motifs to exogenous dsRNA enhances gene silencing in plants, perhaps by stabilizing the dsRNA and/or enhancing its cell-to-cell movement (Kragler et al., 2022). In this project, we are testing if exogenous dsRNA containing tRNA motifs are more effective than unmodified dsRNA at controlling rust pathogens of wheat. We are also investigating the uptake of dsRNA and small interfering RNA (siRNA) into these pathogens, and whether exogenous siRNA may be a more effective approach than dsRNA at controlling these rust pathogens of wheat. Our findings will inform future exogenous RNA design for crop protection against these and other fungal pathogens of plants.