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Lievens EJP, Agarkova IV, Dunigan DD, Van Etten JL, Becks L. Efficient assays to quantify the life history traits of algal viruses. Appl Environ Microbiol 2023; 89:e0165923. [PMID: 38092674 PMCID: PMC10734466 DOI: 10.1128/aem.01659-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Accepted: 09/27/2023] [Indexed: 12/22/2023] Open
Abstract
IMPORTANCE Viruses play a crucial role in microbial ecosystems by liberating nutrients and regulating the growth of their hosts. These effects are governed by viral life history traits, i.e., by the traits determining viral reproduction and survival. Understanding these traits is essential to predicting viral effects, but measuring them is generally labor intensive. In this study, we present efficient methods to quantify the full life cycle of lytic viruses. We developed these methods for viruses infecting unicellular Chlorella algae but expect them to be applicable to other lytic viruses that can be quantified by flow cytometry. By making viral phenotypes accessible, our methods will support research into the diversity and ecological effects of microbial viruses.
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Affiliation(s)
- Eva J. P. Lievens
- Aquatic Ecology and Evolution Group, Limnological Institute, University of Konstanz, Konstanz, Germany
| | - Irina V. Agarkova
- Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
- Nebraska Center for Virology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
| | - David D. Dunigan
- Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
- Nebraska Center for Virology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
| | - James L. Van Etten
- Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
- Nebraska Center for Virology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
| | - Lutz Becks
- Aquatic Ecology and Evolution Group, Limnological Institute, University of Konstanz, Konstanz, Germany
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Noel EA, Weeks DP, Van Etten JL. Pursuit of chlorovirus genetic transformation and CRISPR/Cas9-mediated gene editing. PLoS One 2021; 16:e0252696. [PMID: 34673785 PMCID: PMC8530361 DOI: 10.1371/journal.pone.0252696] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Accepted: 09/29/2021] [Indexed: 11/18/2022] Open
Abstract
Genetic and molecular modifications of the large dsDNA chloroviruses, with genomes of 290 to 370 kb, would expedite studies to elucidate the functions of both identified and unidentified virus-encoded proteins. These plaque-forming viruses replicate in certain unicellular, eukaryotic chlorella-like green algae. However, to date, only a few of these algal species and virtually none of their viruses have been genetically manipulated due to lack of practical methods for genetic transformation and genome editing. Attempts at using Agrobacterium-mediated transfection of chlorovirus host Chlorella variabilis NC64A with a specially-designed binary vector resulted in successful transgenic cell selection based on expression of a hygromycin-resistance gene, initial expression of a green fluorescence gene and demonstration of integration of Agrobacterium T-DNA. However, expression of the integrated genes was soon lost. To develop gene editing tools for modifying specific chlorovirus CA-4B genes using preassembled Cas9 protein-sgRNA ribonucleoproteins (RNPs), we tested multiple methods for delivery of Cas9/sgRNA RNP complexes into infected cells including cell wall-degrading enzymes, electroporation, silicon carbide (SiC) whiskers, and cell-penetrating peptides (CPPs). In one experiment two independent virus mutants were isolated from macerozyme-treated NC64A cells incubated with Cas9/sgRNA RNPs targeting virus CA-4B-encoded gene 034r, which encodes a glycosyltransferase. Analysis of DNA sequences from the two mutant viruses showed highly targeted nucleotide sequence modifications in the 034r gene of each virus that were fully consistent with Cas9/RNP-directed gene editing. However, in ten subsequent experiments, we were unable to duplicate these results and therefore unable to achieve a reliable system to genetically edit chloroviruses. Nonetheless, these observations provide strong initial suggestions that Cas9/RNPs may function to promote editing of the chlorovirus genome, and that further experimentation is warranted and worthwhile.
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Affiliation(s)
- Eric A. Noel
- Nebraska Center for Virology, University of Nebraska, Lincoln, Nebraska, United States of America
- School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, United States of America
| | - Donald P. Weeks
- Department of Biochemistry, University of Nebraska, Lincoln, Nebraska, United States of America
| | - James L. Van Etten
- Nebraska Center for Virology, University of Nebraska, Lincoln, Nebraska, United States of America
- Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska, United States of America
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Van Etten JL, Agarkova IV, Dunigan DD. Chloroviruses. Viruses 2019; 12:E20. [PMID: 31878033 PMCID: PMC7019647 DOI: 10.3390/v12010020] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 12/13/2019] [Accepted: 12/15/2019] [Indexed: 12/20/2022] Open
Abstract
Chloroviruses are large dsDNA, plaque-forming viruses that infect certain chlorella-like green algae; the algae are normally mutualistic endosymbionts of protists and metazoans and are often referred to as zoochlorellae. The viruses are ubiquitous in inland aqueous environments throughout the world and occasionally single types reach titers of thousands of plaque-forming units per ml of native water. The viruses are icosahedral in shape with a spike structure located at one of the vertices. They contain an internal membrane that is required for infectivity. The viral genomes are 290 to 370 kb in size, which encode up to 16 tRNAs and 330 to ~415 proteins, including many not previously seen in viruses. Examples include genes encoding DNA restriction and modification enzymes, hyaluronan and chitin biosynthetic enzymes, polyamine biosynthetic enzymes, ion channel and transport proteins, and enzymes involved in the glycan synthesis of the virus major capsid glycoproteins. The proteins encoded by many of these viruses are often the smallest or among the smallest proteins of their class. Consequently, some of the viral proteins are the subject of intensive biochemical and structural investigation.
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Affiliation(s)
- James L. Van Etten
- Department of Plant Pathology, Nebraska Center for Virology, University of Nebraska-Lincoln, Lincoln, NE 68583-0900, USA; (I.V.A.); (D.D.D.)
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Gould SB, Garg SG, Handrich M, Nelson-Sathi S, Gruenheit N, Tielens AGM, Martin WF. Adaptation to life on land at high O 2 via transition from ferredoxin-to NADH-dependent redox balance. Proc Biol Sci 2019; 286:20191491. [PMID: 31431166 PMCID: PMC6732389 DOI: 10.1098/rspb.2019.1491] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Pyruvate : ferredoxin oxidoreductase (PFO) and iron only hydrogenase ([Fe]-HYD) are common enzymes among eukaryotic microbes that inhabit anaerobic niches. Their function is to maintain redox balance by donating electrons from food oxidation via ferredoxin (Fd) to protons, generating H2 as a waste product. Operating in series, they constitute a soluble electron transport chain of one-electron transfers between FeS clusters. They fulfil the same function—redox balance—served by two electron-transfers in the NADH- and O2-dependent respiratory chains of mitochondria. Although they possess O2-sensitive FeS clusters, PFO, Fd and [Fe]-HYD are also present among numerous algae that produce O2. The evolutionary persistence of these enzymes among eukaryotic aerobes is traditionally explained as adaptation to facultative anaerobic growth. Here, we show that algae express enzymes of anaerobic energy metabolism at ambient O2 levels (21% v/v), Chlamydomonas reinhardtii expresses them with diurnal regulation. High O2 environments arose on Earth only approximately 450 million years ago. Gene presence/absence and gene expression data indicate that during the transition to high O2 environments and terrestrialization, diverse algal lineages retained enzymes of Fd-dependent one-electron-based redox balance, while the land plant and land animal lineages underwent irreversible specialization to redox balance involving the O2-insensitive two-electron carrier NADH.
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Affiliation(s)
- S B Gould
- Institute for Molecular Evolution, Heinrich Heine University Düsseldorf, 40225 Düsseldorf, Germany
| | - S G Garg
- Institute for Molecular Evolution, Heinrich Heine University Düsseldorf, 40225 Düsseldorf, Germany
| | - M Handrich
- Institute for Molecular Evolution, Heinrich Heine University Düsseldorf, 40225 Düsseldorf, Germany
| | - S Nelson-Sathi
- Interdisciplinary Biology, Computational Biology Laboratory, Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram, India
| | - N Gruenheit
- Institute for Molecular Evolution, Heinrich Heine University Düsseldorf, 40225 Düsseldorf, Germany
| | - A G M Tielens
- Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.,Department of Medical Microbiology and Infectious Diseases, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - W F Martin
- Institute for Molecular Evolution, Heinrich Heine University Düsseldorf, 40225 Düsseldorf, Germany
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Yu S, Zheng C, Zhou F, Baillie DL, Rose AM, Deng Z, Chu JSC. Genomic identification and functional analysis of essential genes in Caenorhabditis elegans. BMC Genomics 2018; 19:871. [PMID: 30514206 PMCID: PMC6278001 DOI: 10.1186/s12864-018-5251-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2018] [Accepted: 11/14/2018] [Indexed: 11/27/2022] Open
Abstract
Background Essential genes are required for an organism’s viability and their functions can vary greatly, spreading across many pathways. Due to the importance of essential genes, large scale efforts have been undertaken to identify the complete set of essential genes and to understand their function. Studies of genome architecture and organization have found that genes are not randomly disturbed in the genome. Results Using combined genetic mapping, Illumina sequencing, and bioinformatics analyses, we successfully identified 44 essential genes with 130 lethal mutations in genomic regions of C. elegans of around 7.3 Mb from Chromosome I (left). Of the 44 essential genes, six of which were genes not characterized previously by mutant alleles, let-633/let-638 (B0261.1), let-128 (C53H9.2), let-511 (W09C3.4), let-162 (Y47G6A.18), let-510 (Y47G6A.19), and let-131 (Y71G12B.6). Examine essential genes with Hi-C data shows that essential genes tend to cluster within TAD units rather near TAD boundaries. We have also shown that essential genes in the left half of chromosome I in C. elegans function in enzyme and nucleic acid binding activities during fundamental processes, such as DNA replication, transcription, and translation. From protein-protein interaction networks, essential genes exhibit more protein connectivity than non-essential genes in the genome. Also, many of the essential genes show strong expression in embryos or early larvae stages, indicating that they are important to early development. Conclusions Our results confirmed that this work provided a more comprehensive picture of the essential gene and their functional characterization. These genetic resources will offer important tools for further heath and disease research. Electronic supplementary material The online version of this article (10.1186/s12864-018-5251-3) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Shicheng Yu
- Key Laboratory of Combinatorial Biosynthesis and Drug Discovery, Ministry of Education, School of Pharmaceutical Sciences, Wuhan University, Wuhan, 430071, China. .,Wuhan Frasergen Bioinformatics, Wuhan East Lake High-tech Zone, Wuhan, 430075, China.
| | - Chaoran Zheng
- Key Laboratory of Combinatorial Biosynthesis and Drug Discovery, Ministry of Education, School of Pharmaceutical Sciences, Wuhan University, Wuhan, 430071, China
| | - Fan Zhou
- Wuhan Frasergen Bioinformatics, Wuhan East Lake High-tech Zone, Wuhan, 430075, China
| | - David L Baillie
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada
| | - Ann M Rose
- Department of Medical Genetics, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - Zixin Deng
- Key Laboratory of Combinatorial Biosynthesis and Drug Discovery, Ministry of Education, School of Pharmaceutical Sciences, Wuhan University, Wuhan, 430071, China.
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Viruses of Eukaryotic Algae: Diversity, Methods for Detection, and Future Directions. Viruses 2018; 10:v10090487. [PMID: 30208617 PMCID: PMC6165237 DOI: 10.3390/v10090487] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Revised: 09/04/2018] [Accepted: 09/07/2018] [Indexed: 11/16/2022] Open
Abstract
The scope for ecological studies of eukaryotic algal viruses has greatly improved with the development of molecular and bioinformatic approaches that do not require algal cultures. Here, we review the history and perceived future opportunities for research on eukaryotic algal viruses. We begin with a summary of the 65 eukaryotic algal viruses that are presently in culture collections, with emphasis on shared evolutionary traits (e.g., conserved core genes) of each known viral type. We then describe how core genes have been used to enable molecular detection of viruses in the environment, ranging from PCR-based amplification to community scale "-omics" approaches. Special attention is given to recent studies that have employed network-analyses of -omics data to predict virus-host relationships, from which a general bioinformatics pipeline is described for this type of approach. Finally, we conclude with acknowledgement of how the field of aquatic virology is adapting to these advances, and highlight the need to properly characterize new virus-host systems that may be isolated using preliminary molecular surveys. Researchers can approach this work using lessons learned from the Chlorella virus system, which is not only the best characterized algal-virus system, but is also responsible for much of the foundation in the field of aquatic virology.
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Prasinovirus Attack of Ostreococcus Is Furtive by Day but Savage by Night. J Virol 2018; 92:JVI.01703-17. [PMID: 29187539 PMCID: PMC5790953 DOI: 10.1128/jvi.01703-17] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Accepted: 11/09/2017] [Indexed: 12/12/2022] Open
Abstract
Prasinoviruses are large DNA viruses that infect diverse genera of green microalgae worldwide in aquatic ecosystems, but molecular knowledge of their life cycles is lacking. Several complete genomes of both these viruses and their marine algal hosts are now available and have been used to show the pervasive presence of these species in microbial metagenomes. We have analyzed the life cycle of Ostreococcus tauri virus 5 (OtV5), a lytic virus, using transcriptome sequencing (RNA-Seq) from 12 time points of healthy or infected Ostreococcus tauri cells over a day/night cycle in culture. In the day, viral gene transcription remained low while host nitrogen metabolism gene transcription was initially strongly repressed for two successive time points before being induced for 8 h, but during the night, viral transcription increased steeply while host nitrogen metabolism genes were repressed and many host functions that are normally reduced in the dark appeared to be compensated either by genes expressed from the virus or by increased expression of a subset of 4.4% of the host's genes. Some host cells underwent lysis progressively during the night, but a larger proportion were lysed the following morning. Our data suggest that the life cycles of algal viruses mirror the diurnal rhythms of their hosts.IMPORTANCE Prasinoviruses are common in marine environments, and although several complete genomes of these viruses and their hosts have been characterized, little is known about their life cycles. Here we analyze in detail the transcriptional changes occurring over a 27-h-long experiment in a natural diurnal rhythm, in which the growth of host cells is to some extent synchronized, so that host DNA replication occurs late in the day or early in the night and cell division occurs during the night. Surprisingly, viral transcription remains quiescent over the daytime, when the most energy (from light) is available, but during the night viral transcription activates, accompanied by expression of a few host genes that are probably required by the virus. Although our experiment was accomplished in the lab, cyclical changes have been documented in host transcription in the ocean. Our observations may thus be relevant for eukaryotic phytoplankton in natural environments.
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Moniruzzaman M, Wurch LL, Alexander H, Dyhrman ST, Gobler CJ, Wilhelm SW. Virus-host relationships of marine single-celled eukaryotes resolved from metatranscriptomics. Nat Commun 2017; 8:16054. [PMID: 28656958 PMCID: PMC5493757 DOI: 10.1038/ncomms16054] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Accepted: 05/16/2017] [Indexed: 01/12/2023] Open
Abstract
Establishing virus–host relationships has historically relied on culture-dependent approaches. Here we report on the use of marine metatranscriptomics to probe virus–host relationships. Statistical co-occurrence analyses of dsDNA, ssRNA and dsRNA viral markers of polyadenylation-selected RNA sequences from microbial communities dominated by Aureococcus anophagefferens (Quantuck Bay, NY), and diatoms (Narragansett Bay, RI) show active infections by diverse giant viruses (NCLDVs) associated with algal and nonalgal hosts. Ongoing infections of A. anophagefferens by a known Mimiviridae (AaV) occur during bloom peak and decline. Bloom decline is also accompanied by increased activity of viruses other than AaV, including (+) ssRNA viruses. In Narragansett Bay, increased temporal resolution reveals active NCLDVs with both ‘boom-and-bust’ and ‘steady-state infection’-like ecologies that include known as well as novel virus–host interactions. Our approach offers a method for screening active viral infections and develops links between viruses and their potential hosts in situ. Our observations further demonstrate that previously unknown virus–host relationships in marine systems are abundant. Viruses are partners in ecosystem ecology, yet their study has been primarily limited to laboratory models virus-host or derived from metagenomics. Here, Moniruzzaman et al. use metatranscriptomics to resolve interactions between giant viruses and single-celled eukaryotic hosts.
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Affiliation(s)
- Mohammad Moniruzzaman
- Department of Microbiology, The University of Tennessee, Knoxville, Tennessee 37996, USA
| | - Louie L Wurch
- Department of Biology, James Madison University, Harrisonburg, Virginia 22807, USA
| | - Harriet Alexander
- Department of Earth and Environmental Science and Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA
| | - Sonya T Dyhrman
- Department of Earth and Environmental Science and Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA
| | - Christopher J Gobler
- School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, New York 11794, USA
| | - Steven W Wilhelm
- Department of Microbiology, The University of Tennessee, Knoxville, Tennessee 37996, USA
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Han GZ. Evolution of jasmonate biosynthesis and signaling mechanisms. JOURNAL OF EXPERIMENTAL BOTANY 2017; 68:1323-1331. [PMID: 28007954 DOI: 10.1093/jxb/erw470] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Jasmonates are phytohormones that modulate a wide spectrum of plant physiological processes, especially defense against herbivores and necrotrophs. The molecular mechanisms of jasmonate biosynthesis and signaling have been well characterized in model plants. In this review, we provide an in-depth analysis and overview of the origin and evolution of the jasmonate biosynthesis and signaling pathways. Furthermore, we discuss the striking parallels between jasmonate and auxin signaling mechanisms, which reveals a common ancestry of these signaling mechanisms. Finally, we highlight the importance of studying jasmonate biosynthesis and signaling in lower plants.
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Affiliation(s)
- Guan-Zhu Han
- Jiangsu Key Laboratory for Microbes and Functional Genomics, Jiangsu Engineering and Technology Research Center for Microbiology, College of Life Sciences, Nanjing Normal University, Nanjing, Jiangsu 210046, China
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Blanc G, Mozar M, Agarkova IV, Gurnon JR, Yanai-Balser G, Rowe JM, Xia Y, Riethoven JJ, Dunigan DD, Van Etten JL. Deep RNA sequencing reveals hidden features and dynamics of early gene transcription in Paramecium bursaria chlorella virus 1. PLoS One 2014; 9:e90989. [PMID: 24608750 PMCID: PMC3946568 DOI: 10.1371/journal.pone.0090989] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Accepted: 02/05/2014] [Indexed: 11/18/2022] Open
Abstract
Paramecium bursaria chlorella virus 1 (PBCV-1) is the prototype of the genus Chlorovirus (family Phycodnaviridae) that infects the unicellular, eukaryotic green alga Chlorella variabilis NC64A. The 331-kb PBCV-1 genome contains 416 major open reading frames. A mRNA-seq approach was used to analyze PBCV-1 transcriptomes at 6 progressive times during the first hour of infection. The alignment of 17 million reads to the PBCV-1 genome allowed the construction of single-base transcriptome maps. Significant transcription was detected for a subset of 50 viral genes as soon as 7 min after infection. By 20 min post infection (p.i.), transcripts were detected for most PBCV-1 genes and transcript levels continued to increase globally up to 60 min p.i., at which time 41% or the poly (A+)-containing RNAs in the infected cells mapped to the PBCV-1 genome. For some viral genes, the number of transcripts in the latter time points (20 to 60 min p.i.) was much higher than that of the most highly expressed host genes. RNA-seq data revealed putative polyadenylation signal sequences in PBCV-1 genes that were identical to the polyadenylation signal AAUAAA of green algae. Several transcripts have an RNA fragment excised. However, the frequency of excision and the resulting putative shortened protein products suggest that most of these excision events have no functional role but are probably the result of the activity of misled splicesomes.
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Affiliation(s)
- Guillaume Blanc
- Laboratoire Information Structurale and Génomique UMR7256 CNRS, Aix-Marseille Université, Marseille, France
- * E-mail:
| | - Michael Mozar
- Laboratoire Information Structurale and Génomique UMR7256 CNRS, Aix-Marseille Université, Marseille, France
| | - Irina V. Agarkova
- Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska, United States of America
- Nebraska Center for Virology, University of Nebraska, Lincoln, Nebraska, United States of America
| | - James R. Gurnon
- Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska, United States of America
| | - Giane Yanai-Balser
- Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska, United States of America
| | - Janet M. Rowe
- Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska, United States of America
- Nebraska Center for Virology, University of Nebraska, Lincoln, Nebraska, United States of America
| | - Yuannan Xia
- Center for Biotechnology, University of Nebraska, Lincoln, Nebraska, United States of America
| | - Jean-Jack Riethoven
- Center for Biotechnology, University of Nebraska, Lincoln, Nebraska, United States of America
| | - David D. Dunigan
- Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska, United States of America
- Nebraska Center for Virology, University of Nebraska, Lincoln, Nebraska, United States of America
| | - James L. Van Etten
- Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska, United States of America
- Nebraska Center for Virology, University of Nebraska, Lincoln, Nebraska, United States of America
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