Brome mosaic virus (BMV) packages its genomic and subgenomic RNAs into three separate viral particles. BMV purified from barley, wheat and tobacco have distinct relative abundances of the encapsidated RNAs. We seek to identify the basis for the host-dependent differences in viral RNA encapsidation. Sequencing of the viral RNAs revealed recombination events in the 3′ untranslated region of RNA1 of BMV purified from barley and wheat, but not from tobacco. However, the relative amounts of the BMV RNAs that accumulated in barley and wheat are similar and RNA accumulation is not sufficient to account for the difference in RNA encapsidation. Virions purified from barley and wheat were found to differ in their isoelectric points, resistance to proteolysis, and contacts between the capsid residues and the RNA. Mass spectrometric analyses revealed that virions from the three hosts had different post-translational modifications that should impact the physiochemical properties of the virions. Another major source of variation in RNA encapsidation was due to the purification of BMV particles to homogeneity. Highly enriched BMV present in lysates had a surprising range of sizes, buoyant densities, and distinct relative amounts of encapsidated RNAs. These results show that the encapsidated BMV RNAs reflect a combination of host effects on the physiochemical properties of the viral capsids and the enrichment of a subset of virions. The previously unexpected heterogeneity in BMV should influence the timing of the infection and also the host innate immune responses.
The four brome mosaic virus (BMV) RNAs (RNA1 to RNA4) are encapsidated in three distinct virions that have different disassembly rates in infection. The mechanism for the differential release of BMV RNAs from virions is unknown, since 180 copies of the same coat protein (CP) encapsidate each of the BMV genomic RNAs. Using mass spectrometry, we found that the BMV CP contains a complex pattern of posttranslational modifications. Treatment with phosphatase was found to not significantly affect the stability of the virions containing RNA1 but significantly impacted the stability of the virions that encapsidated BMV RNA2 and RNA3/4. Cryo-electron microscopy reconstruction revealed dramatic structural changes in the capsid and the encapsidated RNA. A phosphomimetic mutation in the flexible N-terminal arm of the CP increased BMV RNA replication and virion produc- T he timing of viral genome release into the infected host cell is critically important to the outcome of infection, as it initiates the race between viral processes and the cellular immune responses against the virus. Even small changes in the timing of viral genome release can result in decreased fitness of the virus (1, 2). The regulation of the release of the viral RNAs is poorly understood, especially for icosahedral viruses.Brome mosaic virus (BMV) is a plant-infecting RNA virus that has served as a model system to study the regulation of RNA virus infection (3). A particularly intriguing feature of BMV is that its tripartite positive-strand RNA genome is encapsidated in three distinct virions. All three virions are required for successful infection. Upon entry into cells, RNA1 and RNA2 direct the translation of the viral replication-associated proteins, while RNA3 encodes the movement protein required for cell-to-cell spread and the coat protein (CP). The CP is translated from subgenomic RNA4. In a typical infection, RNA4 is coencapsidated with RNA3 in a 1:1 ratio (4), although the host species can influence the encapsidation of the viral RNAs (5).The BMV CP has multiple regulatory activities during infection (6, 7). Each BMV capsid contains 180 subunits of the CP arranged in a Tϭ3 symmetry. A CP subunit has structural features similar to those of a histone protein. Both have an intrinsically disordered N-terminal arm rich in positively charged residues followed by sequences that fold into a globular domain (7). The N-terminal arm contributes to the differential encapsidation of BMV RNA, has the ability to translocate from the internal cavity to the outside of the virion, and is preferentially cleaved during proteolysis (8,9). Virions formed by CPs that lack the first 8 residues were found to encapsidate RNA2 well but were labile for the encapsidation of RNA1 (8).The BMV virions can be separated by their density into two populations, one enriched for virions containing RNA1, called B1 virions, and the other enriched for virions that encapsidate RNA2 and RNA3/4, called B2.3/4 virions (9). The B1 virions release RNA1 more rapidly than the B2.3/4 v...
In the brome mosaic virus (BMV) virion, the coat protein (CP) selectively contacts the RNA motifs that regulate translation and RNA replication (Hoover et al., 2016. J. Virol. 90, 7748). We hypothesize that the unstructured N-terminal arm (NTA) of the BMV CP can specifically recognize RNA motifs. Using ion mobility spectrometry-mass spectrometry, we demonstrate that peptides containing the NTA of the CP were found to preferentially bind to an RNA hairpin motif that directs the initiation of BMV RNA synthesis. RNA binding causes the peptide to change from heterogeneous structures to a single family of structures. Fluorescence anisotropy, fluorescence quenching and size exclusion chromatography experiments all confirm that the NTA can specific recognize the RNA motif. The peptide introduced into plants along with BMV virion increased accumulation of the BMV CP and accelerated the rate of minus-strand RNA synthesis. The intrinsically disordered BMV NTA could thus specifically recognize BMV RNAs to affect viral infection.
Brome mosaic virus (BMV) (the Russian strain) infects monocot plants and has been studied extensively in barley and wheat. Here, we report BMV can systemically infect rice (Oryza sativa var. japonica), including cultivars in which the genomes have been determined. The BMV capsid protein can be found throughout the inoculated plants. However, infection in rice exhibits delayed symptom expression or no symptoms when compared with wheat (Triticum aestivum). The sequences of BMV RNAs isolated from rice did not reveal any nucleotide changes in RNA1 or RNA2, while RNA3 had only one synonymous nucleotide change from the inoculum sequence. Preparations of purified BMV virions contained RNA1 at a significantly reduced level relative to the other two RNAs. Analysis of BMV RNA replication in rice revealed that minus-strand RNA1 was replicated at a reduced rate when compared with RNA2. Thus, rice appears to either inhibit RNA1 replication or lacks a sufficient amount of a factor needed to support efficient RNA1 replication.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.