A Novel Partitivirus That Confers Hypovirulence on Plant Pathogenic Fungi

Abstract

Members of the family Partitiviridae have bisegmented double-stranded RNA (dsRNA) genomes and are not generally known to cause obvious symptoms in their natural hosts. An unusual partitivirus, Sclerotinia sclerotiorum partitivirus 1 (SsPV1/WF-1), conferred hypovirulence on its natural plant-pathogenic fungal host, Sclerotinia sclerotiorum strain WF-1. Cellular organelles, including mitochondria, were severely damaged. Hypovirulence and associated traits of strain WF-1 and SsPV1/WF-1 were readily cotransmitted horizontally via hyphal contact to different vegetative compatibility groups of S. sclerotiorum and interspecifically to Sclerotinia nivalis and Sclerotinia minor. S. sclerotiorum strain 1980 transfected with purified SsPV1/WF-1 virions also exhibited hypovirulence and associated traits similar to those of strain WF-1. Moreover, introduction of purified SsPV1/WF-1 virions into strain KY-1 of Botrytis cinerea also resulted in reductions in virulence and mycelial growth and, unexpectedly, enhanced conidial production. However, virus infection suppressed hyphal growth of most germinating conidia of B. cinerea and was eventually lethal to infected hyphae, since very few new colonies could develop following germ tube formation. Taken together, our results support the conclusion that SsPV1/WF-1 causes hypovirulence in Sclerotinia spp. and B. cinerea. Cryo-EM (cryo-electron microscopy) reconstruction of the SsPV1 particle shows that it has a distinct structure with similarity to the closely related partitiviruses Fusarium poae virus 1 and Penicillium stoloniferum virus F. These findings provide new insights into partitivirus biological activities and clues about molecular interactions between partitiviruses and their hosts. IMPORTANCEMembers of the Partitiviridae are believed to occur commonly in their phytopathogenic fungal and plant hosts. However, most partitiviruses examined so far appear to be associated with latent infections. Here we report a partitivirus, SsPV1/WF-1, that was isolated from a hypovirulent strain of Sclerotinia sclerotiorum and describe its biological and molecular features. We have demonstrated that SsPV1 confers hypovirulence. Furthermore, SsPV1 can infect and cause hypovirulence in Botrytis cinerea. Our study also suggests that SsPV1 has a vigorous ability to proliferate and spread via hyphal contact. SsPV1 can overcome vegetative incompatibility barriers and can be transmitted horizontally among different vegetative compatibility groups of S. sclerotiorum, even interspecifically. Cryo-EM reconstruction of SsPV1 shows that it has a distinct structure with similarity to closely related partitiviruses. Our studies exploit a novel system, SsPV1 and its hosts, which can provide the means to explore the mechanisms by which partitiviruses interact with their hosts.

Novel Hypovirulence-Associated RNA Mycovirus in the Plant-Pathogenic Fungus Botrytis cinerea: Molecular and Biological Characterization

“…Among these mycoviruses, BcMV1 is closely associated with hypovirulence of B. cinerea (23,24). Moreover, Xiao et al (25) reported that the dsRNA mycovirus Sclerotinia sclerotiorum partitivirus 1 (SsPV1) in strain WF-1 of S. sclerotiorum can infect B. cinerea, resulting in reduced virulence, suppressed mycelial growth, and inhibited elongation of conidial germ tubes.…”

“…Despite the strong evidence of negative correlation, a cause-effect relationship between BcRV1 infection and hypovirulence still needs to be further ascertained in future studies. Two methods, the virion transfection method and the infectious viral cDNA method, have been successfully used in previous studies to elucidate the cause-effect relationship between mycovirus infection and fungal hypovirulence (3,15,25,31,53). These approaches might be useful in future studies for determination of the causal effect of BcRV1 on hypovirulence in B. cinerea.…”

Transfection of Sclerotinia sclerotiorum with In Vitro Transcripts of a Naturally Occurring Interspecific Recombinant of Sclerotinia sclerotiorum Hypovirus 2 Significantly Reduces Virulence of the Fungus

“…However, the diseases caused by S. sclerotiorum have not been adequately controlled by conventional technologies thus far (4,5). A number of mycoviruses have been molecularly characterized and associated with attenuation of the virulence of S. sclerotiorum, including a DNA virus (6, 7), a negative-sense RNA virus (8), mitoviruses (9,10), and double-stranded RNA (dsRNA) (11) and single-stranded positive-sense RNA [ss(ϩ)RNA)] viruses (12)(13)(14)(15)(16)(17). Given the observations that mycoviruses transmitted intercellularly through hyphal anastomosis and extracellularly via viral particles can induce hypovirulence in S. sclerotiorum (7,18), mycoviruses offer a promising approach to reduce crop damage caused by the fungus.…”

Characterization of a Novel Megabirnavirus from Sclerotinia sclerotiorum Reveals Horizontal Gene Transfer from Single-Stranded RNA Virus to Double-Stranded RNA Virus

“…Protoplast preparation of virus-free S. sclerotiorum strain Ep-1PNA367 was performed according to a previously described method (31). Purified VLPs (5 l; about 50 to 200 ng) were introduced into protoplasts (about 10 6 /ml) using polyethylene glycol 4000 (PEG 4000) as previously described (21). Transfected protoplasts were individually transferred to new PDA plates and incubated at 20°C until regenerated mycelia covered the surface of PDA plates.…”

“…Viruslike particles (VLPs) were isolated from mycelia of strain SX466 via differential centrifugation and concentrated by sucrose density gradient centrifugation as previously described with minor modifications (5,21). The VLPs were suspended in 100 l of 0.05 M sodium phosphate buffer (pH 7.4) and then used for SDS-PAGE, polypeptide mass fingerprint-mass spectrum (PMF-MS) analyses, transmission electron microscope (TEM) observations, dsRNA extraction, and infectivity assays.…”