- Author: Kathy Keatley Garvey
It did: their research revealed how TSWV (family Tospoviridae, order Bunyavirales) packages its RNA genome, a crucial step in virus infection.
Their newly published research, “The Genome of a Bunyavirus Cannot be Defined at the Level of the Viral Particle But Only at the Scale of the Viral Population,” appears in the current edition of the Proceedings of the National Academy of Sciences (PNAS).
The 18-member research team included scientists primarily from the French National Research Institute for Agriculture, Food and Environment (INRAE) at the Campus International de Baillarguet, Montpellier; Department of Entomology, University of Wisconsin; and the Department of Entomology and Nematology, University of California, Davis.
“Our work showed the genome of TSWV can only be defined at the population level, pointing at emerging properties when viral particles infect plants in groups,” said a key author Stéphane Blanc, research director of INRAE's Biology and Genetics of Plant-Pathogen Interactions. “As most virions contain an incomplete genome, TSWV is a multi-component viral system, where co-infection and complementation are key in the life cycle. These findings open a myriad of possibly distinct properties depending on the genetic composition of the group of virions co-infecting a cell.”
“The most challenging part of this work was to create a protocol reliably quantifying the two polarities of each segment,” said lead author Michel Yvon of INRAE. “The next important advance will be to demonstrate that co-infection of cells by a group of particles is key to the spread of infection.”
Ullman, an international authority on orthotospoviruses and one of the four main authors, took a sabbatical to work on the project. “My interest was in understanding how TSWV packaged its RNA genome,” she said. “While this sounds like a simple goal, it is quite complex because TSWV has negative sense and ambisense viral strands and many research tools common to studying other viruses, such as infectious clones were not available.”
“It was a delight to work with the fantastic team of scientists that Stéphane assembled, all very talented with skills in virology, cryoelectron microscopy and nanopore PCR,” Ullman commented. “I cannot imagine a more talented and diverse group of people to conduct this difficult work. I learned a great deal about virus purification from Michel Yvon, whose leadership, skills in virology, and patient teaching really moved our project forward."
German, professor emeritus and former chair of both the Departments of Plant Pathology and Entomology at the University of Wisconsin, died Aug. 27, 2023 at age 82.
“I am indebted to my husband, Jean-Marc Leininger who frequently drove me to the laboratory in Avignon where I was able to rear thousands of virus-infected plants and to store TSWV isolate,” Ullman added. “Jean-Marc not only transported me and my virus specimens, but also learned to mechanically inoculate plants and helped with every inoculation and virus harvest.”
UC Davis postdoctoral scholar Sulley Ben-Mahmoud of the Ullman lab was among the co-authors.
Funding was provided by grants from Montpellier University of Excellence (MUSE); Floriculture and Nursery Research Initiative, U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS); and the Fulbright Scholar Program. The authors also acknowledged support from
- Santé des Plantes et Environnementor Plant Health and Environment (SPE)
- Centre National de la Recherche Scientifique (CNRS)
- Institute of Research for Development (IRD)
- Institut national de la santé et de la recherche médicale (INSERM)
- Centre for International Cooperation in Agronomic Research for Development (CIRAD)
- Plant Health Institute of Montpelier (PHIM)
Ullman noted the importance of the research in her Fulbright application: “Sustainable management of insect-transmitted pathogens is a key concern for food production in France and the United States. Both countries grow many of the same crops and growers face similar challenges from insect-transmitted plant viruses. Current management strategies rely heavily on pesticides that may cause significant health and environmental concerns, including damage to bees and other pollinators, as shown with neonicotinoid pesticides. Clearly, better knowledge about these insect-transmitted viral systems…has potential to reduce pesticide use by providing novel and innovative technologies to manage orthotospoviruses and thrips in France and the United States.”
Ullman, a former chair of the Department of Entomology and a former associate dean of the UC Davis College of Agricultural and Environmental Sciences, anticipates strong research relationships between UC Davis and Montpellier that will lead to grant applications for international research and scholarly exchange opportunities for scientists, students, and post-doctoral scholars.
Significance
In their significance statement, the authors wrote: “Bunyaviruses infect animals, plants, fungi, and protists. Despite their importance, fundamental aspects of their biology as basic as the definition of their genome remain elusive. The viral genome consists of several negative or ambisense RNA segments, and virions often miss segments and/or package complementary strands. We formally quantify this heterogeneity on the species Tomato spotted wilt orthotospovirus. Within individual virus particles, the number, the identity, and the polarity of the segments are widely variable. In contrast, we show that a stable genetic composition is an emerging property of the viral population, each of the RNA segments/polarities accumulating reproducibly at a specific frequency. This resembles the genome formula of multipartite viruses, suggesting that bunyaviruses may also function as multicomponent viral systems.”
Their abstract: “Bunyaviruses are enveloped negative or ambisense single-stranded RNA viruses with a genome divided into several segments. The canonical view depicts each viral particle packaging one copy of each genomic segment in one polarity named the viral strand. Several opposing observations revealed nonequal ratios of the segments, uneven number of segments per virion, and even packaging of viral complementary strands. Unfortunately, these observations result from studies often addressing other questions, on distinct viral species, and not using accurate quantitative methods. Hence, what RNA segments and strands are packaged as the genome of any bunyavirus remains largely ambiguous. We addressed this issue by first investigating the virion size distribution and RNA content in populations of the tomato spotted wilt virus (TSWV) using microscopy and tomography. These revealed heterogeneity in viral particle volume and amount of RNA content, with a surprising lack of correlation between the two. Then, the ratios of all genomic segments and strands were established using RNA sequencing and qRT-PCR. Within virions, both plus and minus strands (but no mRNA) are packaged for each of the three L, M, and S segments, in reproducible nonequimolar proportions determined by those in total cell extracts. These results show that virions differ in their genomic content but together build up a highly reproducible genetic composition of the viral population. This resembles the genome formula described for multipartite viruses, with which some species of the order Bunyavirales may share some aspects of the way of life, particularly emerging properties at a supravirion scale.”
- Author: Kathy Keatley Garvey
He will be hosted by colleague and collaborator Diane Ullman, professor of entomology at UC Davis.
"Thrips-transmitted, tomato spotted wilt virus (TSWV), which has an extremely broad host range and is transmitted exclusively by thrips, ranks among the most economically important plant viruses affecting crops worldwide," Kennedy says in his abstract.
"Effective management of this virus in commercial crop production systems requires an understanding of the factors that determine the timing and magnitude of virus spread. This seminar will discuss the ways in which seasonal weather events influence the dispersal dynamics of vector thrips populations, the abundance of virus inoculum sources in the landscape, and ultimately the timing and magnitude of TSWV spread into susceptible crops. It will further provide an illustration of how efforts to model these relationships improved understanding of the epidemiology of TSWV and led to the development of a TSWV risk prediction tool that is now being used in pest management decision making."
Kennedy, past president of the Entomological Society of America (ESA), is an ESA fellow, recipient of the ESA's Award for Excellence in Entomology and chaired the Entomological Foundation, a non-profit educational foundation whose mission is “to excite and educate young people about science through insects.”
He also served as program manager for the National Research Initiative, affiliated with the U.S. Department of Agriculture (USDA), and on numerous advisory panels for the USDA, U.S. Environmental Protection Agency and the National Research Council, addressing issues relating to pesticides, pest resistance, integrated pest management, and biotechnology.
Kennedy holds a bachelor's degree in entomology from Oregon State University and a doctorate in entomology from Cornel University. He served as assistant professor of entomology at UC Riverside from 1974-1976, before joining the faculty at North Carolina State University.
See his biosketch on the ESA website.
Kennedy writes on his website: "Research in my program focuses on understanding the ecology and life systems of arthropods affecting agricultural crops and applying that understanding to improve the effectiveness and sustainability of arthropod management in vegetable crops. We study fundamental interactions and processes that influence pest status, population dynamics and the insect/crop interactions that result in damage. We apply the resulting information in combination with new technologies to enhance IPM. Areas of emphasis include insect-plant interactions, resistance management, landscape scale population dynamics, and epidemiology and management of insect transmitted plant viruses. Current research projects focus on understanding the determinants of tospovirus transmission by thrips in relation to epidemiology and management of tomato spotted wilt virus and on the development of reduced risk arthropod management systems for fruiting vegetables. These efforts include both field and laboratory research and collaborations with faculty in Entomology, Horticulture and Plant Pathology at NCSU and colleagues at other institutions. We also work closely with extension colleagues, growers and the agribusiness community to facilitate implementation of new pest management practices."
The seminar will be recorded for later viewing on UCTV Seminars.