Abstract:Apple Valsa canker caused by Valsa mali is a destructive disease of apple trees. MicroRNA-like RNAs (milRNAs) play an important role in fungal growth and development, pathogenicity, and stress responses. Our previous study had demonstrated that the expression of Vm-milR21 was significantly down-regulated in the infection, suggesting Vm-milR21 might be involved in the pathogenicity of V. mali. [Objective] To reveal the role of Vm-milR21. [Methods] The strains with overexpression and silencing of Vm-milR21 precursor were constructed, and the phenotypic characteristics were compared between different transformants and the wild type. Furthermore, the targeting relationship between Vm-milR21 and Vm-03494 was verified by Quantitative real time polymerase chain reaction (qRT-PCR) and co-transformation. On this basis, the mutant with the knockout of Vm-03494 was constructed and the phenotype of the mutant was characterized. [Results] Compared with the wild type, the transformant overexpressing Vm-milR21 precursor presented slow mycelial growth and weakened pathogenicity, while the silencing of Vm-milR21 did not cause significant changes. Vm-milR21 inhibited the expression of Vm-03494 in a sequence-specific manner. Compare with the wild type, the mutant without Vm-03494 presented slow mycelial growth and diminished pathogenicity. [Conclusion] Vm-milR21 plays a role in the infection of V. mali by regulating the expression of Vm-03494. The results enrich the understanding of the functions of fungal milRNAs and provide a new theoretical basis for comprehensively deciphering the pathogenesis of V. mali.
