Novel Mycoviruse of Talaromyces marneffei Enhances Host Virulence by Altering Gene Expression

Abstract

Mycoviruses are found in a wide variety of fungi, from plant pathogenic fungi to human pathogenic fungi. Most mycoviruses cause cryptic infections, while some alter the phenotypes and physiology of their hosts, such as irregular growth, abnormal pigmentation and altered sexual reproduction. The most well­known mycovirus is the CHV1 in Cryphonectrica parasitica and FgV1 in Fusarium graminearum, which both induced hypovirulence of their fungal hosts. However, most of those studies focus on plant pathogenic fungi, their biological role and the potential mechanisms by which they may alter fungal virulence, especially in human­pathogenic fungi, is largely unknown. Here, for the first time, in thermal dimorphic fungi, we report the discovery of a novel partitivirus, Talaromyces marneffei partitivirus­1 (TmPV1), in Talaromyces marneffei, which is the most important opportunistic human pathogenic thermal dimorphic fungus in Southeast Asia. It is regarded as one of the world’s top ten most feared fungi, causing highly fatal systemic infection in HIV­infected and immunocompromised patients. TmPV1 was detected in 12.7% (7of 55) clinical T. marneffei isolates. TmPV1 were then revealed as double­stranded RNA (dsRNA) viruses with 2 segments coding RNA­dependent RNA polymerase (RdRp) and capsid protein. They were showed to belong to a same and novel species of the genus Gammapartitivirus of the family Partitiviridae by phylogenetic analysis. The presence of isometric, nonenveloped viral particles with a diameter of 30 to 45 nm was confirmed in TmPV1­infected T. marneffei by transmission electron microscopy. qRT­PCR showed that the viral load of TmPV1 in the yeast phase of the infected T. marneffei was much higher (2 to 8 folds) than in the mycelial phase. TmPV1 enhanced the virulence of T. marneffei after T. marneffei was infected with purified TmPV1 particles, in mice model. Mouse challenged with these isogenic TmPV1­infected T. marneffei showed significantly shortened lifetime (P< 0.0001), a higher fungal burden in organs, and more severe inflammation in the lung than mice challenged with isogenic TmPV1­free T. marneffei. Transcriptomic analysis showed that TmPV1 upregulated the expression of some potential virulence factors while downregulated the expression of RNA interference (RNAi)­related genes, which may be involved in antiviral defense.