The DNA-A Component of a Plant Geminivirus (Indian Mung Bean Yellow Mosaic Virus) Replicates in Budding Yeast Cells

Abstract

Understanding the biochemistry of DNA replication of the plant DNA viruses is important for the development of antiviral strategies. Since DNA replication is little studied in plants, a genetically tractable, easily culturable, eukaryotic model system is required to pursue such studies in a facile manner. Here we report the development of a yeast model system that supports DNA replication of a chosen geminivirus strain, Indian mung bean yellow mosaic virus. The replication of plasmid DNA in the model system relies specifically on the virus-derived elements and factors. Usage of this model system revealed the role of at least one hitherto unknown viral factor for viral DNA replication. The episomal characteristic of single-strandedness of replicated plasmid DNA was shown, and the expression of viral genes was also confirmed. This model system is expected to shed light on the machinery and mechanism involved in geminiviral DNA replication in plants.The complexities of host features might hinder the addressing of specific issues related to host-virus interactions, including biosynthesis of viral nucleic acids. The factors required for DNA replication of the plant DNA viruses are difficult to discover in a systematic manner by employing the current approaches of plant biology. The variability associated with DNA transfections of plant protoplasts, the problems related to plant transformation, and other issues limit the progress of studies of DNA replication of viruses such as geminiviruses, which are potent phytopathogens. Moreover, the intermediates of replicated products are difficult to isolate from infected plant tissues. The lack of genetic mutants and of sequence information for the host genomes also compounds the problem. In order to circumvent these difficulties, we looked for a model eukaryotic host that supports DNA replication of the geminiviruses.Geminiviruses represent a family of viruses which are characterized by twin icosahedral particles, each of which encapsidates a small (ϳ2.7 kb) single-stranded circular DNA. Though no crop is immune to the geminiviruses, each strain of geminivirus can infect crop plants within a narrow window of host specificity (19). Indian mung bean yellow mosaic virus (IMYMV), a member of the Geminiviridae family, possesses bipartite genomes, namely DNA-A and DNA-B, and is a menace in legume cultivation (18). The 2,745-bp DNA-A component encodes the information for viral DNA replication, transcription, and encapsidation, whereas the 2,616-bp DNA-B encodes two movement proteins responsible for virus translocation.Studies with viruses related to IMYMV have suggested that the viral DNA frequently, but not exclusively, replicates in a rolling circle mode (RCR) (10, 16, 21) The replication origins of all geminiviruses include an invariant 9-mer sequence (TAATATT2AC) which is site-specifically nicked (at the position of the arrow) by a virus-encoded replication initiator protein (Rep; also called AC1 or AL1) to initiate RCR (28). For efficient replication, Rep is assisted by a repl...

A geminivirus-related DNA mycovirus that confers hypovirulence to a plant pathogenic fungus

“…Thus, SsHADV-1 can spread naturally under field conditions. Moreover, we expect that the host range of SsHADV-1 could be expanded to include other important plant pathogens considering that yeast was demonstrated to support replication of the DNA-A component of a plant geminivirus (38). Thus, the potential of SsHDAV-1 as a biological control agent to control plant fungal diseases needs to be explored.…”

Nodamura Virus RNA Replication in Saccharomyces cerevisiae : Heterologous Gene Expression Allows Replication-Dependent Colony Formation

“…To date, FHV and NoV are the only two positive-sense RNA viruses to replicate their entire genomes in yeast, although several other viruses (with RNA or DNA genomes) can undergo partial replication in yeast cells (2,15,26,31,35). NoV is the only virus infectious to mammals able to fully replicate its genome in yeast.…”

“…However, upon experimental transduction, the RNAs of both NoV and FHV will replicate to very high levels in a variety of cell types, including those from mammals, insects, and higher plants (4,30,34). FHV remains the only animal-infectious virus that has been reported to replicate its entire genome and produce infectious virus in the yeast Saccharomyces cerevisiae (30), although several other viruses can undergo partial replication in yeast cells (2,15,26,31,35). The ability to study virus replication in a unicellular organism that can grow under strictly defined conditions greatly facilitates the investigation and utilization of nodaviruses.…”

PCNA Interacts with Indian Mung Bean Yellow Mosaic Virus Rep and Downregulates Rep Activity

“…IMYMV Rep is a site-specific DNA binding, site-specific nicking-closing enzyme and an ATP-activated type I DNA topoisomerase; these biochemical activities are required for the initiation and termination of DNA replication of the IMYMV genome (26,29). Since the coding capacities of the geminivirus DNA genomes are extremely limited, the replication and transmission processes of these viruses are largely dependent on host factors.…”