Exogenous dsRNA-Mediated Control of Rice Blast Fungus Involves Sequence-Specific RNAi and Sequence-Unspecific Fungal Stress Responses

In vertebrates and plants, double-stranded (ds)RNA plays crucial roles as a pathogen-associated molecular pattern (PAMP) and as a mediator of RNA interference (RNAi). However, our understanding of fungal responses to dsRNA remains limited. Here, we demonstrate that Magnaporthe oryzae (Mo), a globally significant crop pathogen, actively internalizes exogenous dsRNA across a broad size range of 21 to about 3000 bp. Treatment of Mo conidia with dsRNA, irrespective of size or sequence, induces aberrant germ tube elongation. Additionally, application of dsRNA to Brachypodium distachyon leaves suppresses disease progression upon Mo infection. Intriguingly, dsRNA elicits canonical stress pathways in Mo, as evidenced by nuclear accumulation of the stress marker mitogen-activated protein kinase Hog1p and the production of reactive oxygen species. However, these sequence-nonspecific effects are transient, while sequence-specific RNAi activity predominates in a preventive intervention scenario, when a time interval of several days between dsRNA application and fungal inoculation is maintained, and dsRNA is stabilized in novel alginate-chitosan nanoparticles. Overall, our data show that the effects of dsRNA on fungi and the diseases they cause can be multifaceted and complex, which has implications for the development and application of dsRNA pesticides in agricultural practice.