Plant-derived, stress-responsive microRNA mimics reduce powdery mildew infections of barley

Barley powdery mildew, caused by Blumeria hordei , leads to economic losses worldwide. Here, in silico analyses and proof-of-concept experiments were conducted to determine if specific plant-derived synthetic microRNAs (miRNAs) may be considered as a new direction for the control of barley powdery mildew. Previous studies have demonstrated that barley miRNAs regulate plant immunity against B. hordei . Based on the predicted targets of stress-responsive miRNAs in barley, four miRNAs that are upregulated during biotic stresses were selected and applied through Spray-Induced Gene Silencing (SIGS). Double-stranded RNA (dsRNA) constructs were designed and synthesized for the four selected miRNAs and sprayed on detached barley leaf segments that were subsequently infected with B. hordei . Visual disease symptoms and the B. hordei micro-colony index were significantly reduced in the treated leaf segments compared to the control. Quantitative PCR analysis confirmed a significant reduction in the relative B. hordei DNA abundance six days post infection. These results confirmed that the selected plant-derived synthetic miRNAs suppress the development of barley powdery mildew under experimental conditions. This is the first study to show that plant-derived, stress-responsive synthetic miRNAs reduced infection caused by fungal pathogens when applied through SIGS. Our approach could be applied in further experiments focusing on functional analyses of miRNAs in a time-efficient manner, and without requiring miRNA overexpression via genetic transformation.