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

The onset of symptoms in virus-infected mushrooms merits investigation. In this study, the influence of heat stress (HS) on the interaction between <i>Lentinula edodes</i> mycovirus HKB (LeV) and its mushroom host, <i>Lentinula edodes</i>, 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 <i>Trichoderma atroviride</i> of <i>L. edodes</i> 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 <i>LE01Gene01783</i>. 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 <i>L. edodes</i> to LeV infection and HS. Based on these findings, a putative mechanism was proposed to elucidate the interplay among temperature, LeV, and <i>L. edodes</i>. 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 <i>Lentinula edodes</i>, upon LeV infection under heat stress, LeV replication surges, triggering degradation of the LeV genome by <i>DCL1</i>, particularly on its 5'-UTR end and ORF1 upstream regions. <i>DCL1</i> and several other RNAi key genes (such as <i>LeAGO8</i>, <i>LeRDR1</i>, <i>LeRDR5</i>, and <i>LeRDR6</i>) are also possibly recruited during the thermotolerance-related host microRNA (<i>led-milR-21</i>) formation, leading to its increased production. Consequently, led-milR-21-dependent silencing of <i>LE01Gene01783</i> 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.