Bidirectional sRNA-trafficking and RNA-based plant protection against Botrytis cinerea and other pathogens that utilize small RNA effectors

The aggressive fungal pathogen Botrytis cinerea causes severe crop losses worldwide. We have discovered that B. cinerea delivers small RNAs (sRNAs) into plant cells to silence host immunity genes. Such sRNA effectors are mainly produced from retrotransposons by B. cinerea Dicer-like (Bc-DCL) proteins. Here we show that expressing sRNAs that target Bc-DCL1 and Bc-DCL2 in Arabidopsis or Solanum lycopersium (tomato) silences Bc-DCL genes and attenuates fungal pathogenicity and growth. This suggests that sRNAs can move from the hosts to the fungus; thus, sRNA trafficking between B. cinerea and its hosts is bidirectional. We demonstrate that Verticillum dahliae, a fungal pathogen that causes wilt disease, also uses sRNA effectors for its virulence. Plants expressing sRNAs that target DCLs of B. cinerea and V. dahliae, show reduced susceptibility to both pathogens. Furthermore, B. cinerea could take up external sRNAs and dsRNAs from the environment. Applying Bc-DCL-targeting sRNAs or the double-stranded RNA (dsRNA) precursors on the surface of fruits, vegetables, or flowers significantly inhibits gray mold disease. These results demonstrate an effective RNAi-based strategy for controlling multiple diseases, which could potentially replace toxic fungicides and also circumvents the need for transgenic plants.