Host-induced gene silencing targeting the calcineurin of Fusarium fujikuroi to enhance resistance against rice bakanae disease

Bakanae, or foolish seedling disease of rice, is caused by the ascomycetous fungus <i>Fusarium fujikuroi</i>, which is prevalent in many rice-growing countries. Current protection strategies depend on fungicides, but this results in chemical-resistant <i>F. fujikuroi</i> and detrimental environmental effects. It is known that calcineurin controls Ca²⁺ signaling, which mediates growth, stress responses, and pathogenicity in fungi. Based on the pharmacological inhibition of calcineurin in <i>F. fujikuroi</i>, we discovered that calcineurin inhibitor FK506 or cyclosporin A can intensely prevent the growth of <i>F. fujikuroi</i>, and further investigated the feasibility of silencing calcineurin genes of <i>F. fujikuroi</i> in rice using host-induced gene silencing (HIGS) to confer resistance to bakanae disease. The constructs <i>FfCNA1-Ri</i> and <i>FfCNB1-Ri</i> were introduced into rice plants by using <i>Agrobacterium</i>-mediated gene transformation, and the copy numbers of transgenes were examined by Southern blot hybridization in the transgenic lines. The results of pathogen inoculation assay and fungal biomass quantification demonstrated that the transgenic rice plants that carry the <i>FfCNA1-Ri</i> or <i>FfCNB1-Ri</i> construct had increased resistance against bakanae disease. We propose that RNAi-derived siRNAs might efficiently suppress the expression of calcineurin genes in <i>F. fujikuroi</i>, leading to impaired growth and poor colonization of <i>F. fujikuroi</i> in rice. These findings indicate that HIGS might be a potential disease management strategy for rice bakanae disease.