Transfection of entomopathogenic Metarhizium species with a novel mycovirus confers hypervirulence against two lepidopteran pests. Transfection of entomopathogenic Metarhizium species with a novel mycovirus confers hypervirulence against two lepidopteran pests

Although most known mycoviruses are asymptomatic or reduce the virulence of their host fungi, those that confer hypervirulence to entomopathogenic fungus still need to be explored. Here, we discovered and studied a novel mycovirus in Metarhizium flavoviride, isolated from Laodelphax striatellus. Based on molecular analysis, we tentatively designated the mycovirus as Metarhizium flavoviride partitivirus 1 (MfPV1), a novel species in genus Gammapartitivirus, family Partitiviridae. MfPV1 has two double-stranded (ds) RNAs as its genome, 1,775 and 1,575 bp in size respectively, encapsidated in isometric particles. When we transfected commercial strains of M. anisopliae and M. pingshaense with MfPV1, conidiation was significantly enhanced (t-test; P-value < 0. 01), and the significantly higher mortality rates of the larvae of Plutella xylostella and Spodoptera frugiperda, two important lepidopteran pests were found in virus-transfected strains (ANOVA; P-value < 0.05). Transcriptomic analysis showed that transcript levels of pathogenesis-related genes in MfPV1-infected M. anisopliae were obviously altered, suggesting increased production of metarhizium adhesin-like protein, hydrolyzed protein and destruxin synthetase. Further studies are required to elucidate the mechanism whereby MfPV1 enhances the expression of pathogenesis-related genes and virulence of Metarhizium to lepidopteran pests. This study presents experimental evidence that the transfection of other entomopathogenic fungal species with a mycovirus can confer significant hypervirulence and provides a good example that mycoviruses could be used as synergistic agent to enhance the biocontrol activity of entomopathogenic fungi. Overall design: To investigate a novel mycovirus induced hypervirulence in the host fungus, we analyzed the RNA-seq data from hyphae of three virus-infected and three virus-free strains of M. anisopliae cultured in cicada slough induced PBD medium.