New insights into temperature-impacted mycovirus-fungus interactions regulated by a microRNA in Lentinula edodes

The onset of symptoms in virus-infected mushrooms merits investigation. In this study, the influence of heat stress (HS) on the interaction between Lentinula edodes mycovirus HKB (LeV) and its mushroom host, Lentinula edodes, was explored, revealing that HS treatment facilitated LeV replication and compromised the host's thermotolerance at full growth of mycelia. Transcriptomic analysis showed that fewer genes responded to HS, and thermotolerance-related genes were downregulated when the virus infection occurred. A host microRNA, led-milR-21, proven as a negative regulator of the growth rate, thermotolerance, and resistance against Trichoderma atroviride of L. edodes mycelia by functional analyses, could be induced by both LeV infection and HS. Tobacco transient expression experiments with qRT-PCR confirmation demonstrated that led-milR-21 targeted a thermotolerance-related transcription factor LE01Gene01783. Further analysis showed that genes associated with tryptophan metabolism, arginine and proline metabolism, valine/leucine and isoleucine degradation, protein processing in the endoplasmic reticulum, fatty acid degradation, and glycerolipid metabolism may play roles in the responses of L. edodes to LeV infection and HS. Based on these findings, a putative mechanism was proposed to elucidate the interplay among temperature, LeV, and L. edodes. This study deepens our understanding of how fruit body-forming fungi respond to viral infection and abiotic stress, providing insights into potential virus-host interactions in a scenario of global warming.IMPORTANCEThis is the first report of a fungal miRNA being induced by a mycovirus. In Lentinula edodes, upon LeV infection under heat stress, LeV replication surges, triggering degradation of the LeV genome by DCL1, particularly on its 5'-UTR end and ORF1 upstream regions. DCL1 and several other RNAi key genes (such as LeAGO8, LeRDR1, LeRDR5, and LeRDR6) are also possibly recruited during the thermotolerance-related host microRNA (led-milR-21) formation, leading to its increased production. Consequently, led-milR-21-dependent silencing of LE01Gene01783 occurs upon LeV infection, diminishing the heat repair capacity. This study deepens our understanding of how fruiting body-forming fungi respond to viral infection and abiotic stress, providing insights into potential virus-host interactions in a scenario of global warming.