Host sRNAs regulate host responses to pathogen infection and are used as early diagnostic markers for many human diseases, including cancers. Huanglongbing (HLB) is a devastating citrus disease that threatens the whole citrus industry worldwide. Powerful diagnostic tools and management strategies are desired to control HLB. Using sRNA profiling, we found that several citrus miRNAs and siRNAs were highly induced by Las infection, and can be potentially developed into early diagnostic markers of HLB. Induction of miR399 led to the discovery of phosphorus deficiency in HLB-positive trees. Applying phosphorus oxyanion solutions largely reduced HLB symptom severity and significantly improved fruit production.
Eukaryotic pathogens also produce sRNAs. However, evidence of their roles in pathogenicity is lacking. Genome-wide sRNA profiling identified a group of sRNAs from Botrytis cinerea that can potentially target important immunity genes in plant hosts, including Arabidopsis and tomato. We found that these Botrytis sRNAs are delivered into host cells and hijack host AGO proteins to silence immunity genes during infection. It’s a general strategy for pathogens to deliver effector proteins into host cell to hamper host immune responses and achieve pathogenicity. Here, we added sRNAs into the list of effector molecules to suppress host immunity and contribute to fungal pathogenicity.