Bidirectional cross-kingdom RNAi and spray-induced gene silencing for plant disease control

Small RNAs (sRNAs) are a class of short non-coding RNAs that mediate gene silencing in a sequence-specific manner. We have demonstrated that some sRNAs from eukaryotic pathogens, such as Botrytis cinerea, the fungal pathogen that causes grey mold disease on more than 1000 plant species, could be translocated into host plant cells and suppress host immunity genes for successful infection. This finding represented the first example of naturally occurring Cross-Kingdom RNAi in host – pathogen interactions. These sRNAs act as a new class of pathogen effectors that translocate into host cells to suppress host immunity. Recently we have found that transgenic plants expressing hairpin RNAs that targeting Botrytis Dicer 1and Dicer 2 genes could effectively block the generation of fungal sRNA effectors and suppress grey mold disease. This strategy can be adapted to simultaneously control multiple fungal diseases. We show that Arabidopsis plants expressing hairpin RNAs that simultaneously target DCL genes of B. cinerea and V. dahliae show enhanced disease resistance to both pathogens. These results also suggest that sRNA trafficking is bi-directional and sRNAs could move from the host cells to the interacting pathogens. Most strikingly, we discovered that Botrytis could take up double-stranded RNAs and sRNAs from the environment. Applying sRNAs or dsRNAs that target Botrytis Dicer genes on the surface of fruits, vegetables and flowers significantly inhibits grey mold disease. Such pathogen gene-targeting RNAs represent a new generation of environmentally friendly fungicides.