title: Analysis of viral (zucchini yellow mosaic virus) genetic diversity during systemic movement through a Cucurbita pepo vine.
abstract: Determining the extent and structure of intra-host genetic diversity and the magnitude and impact of population bottlenecks is central to understanding the mechanisms of viral evolution. To determine the nature of viral evolution following systemic movement through a plant, we performed deep sequencing of 23 leaves that grew sequentially along a single Cucurbita pepo vine that was infected with zucchini yellow mosaic virus (ZYMV), and on a leaf that grew in on a side branch. Strikingly, of 112 genetic (i.e. sub-consensus) variants observed in the data set as a whole, only 22 were found in multiple leaves. Similarly, only three of the 13 variants present in the inoculating population were found in the subsequent leaves on the vine. Hence, it appears that systemic movement is characterized by sequential population bottlenecks, although not sufficient to reduce the population to a single virion as multiple variants were consistently transmitted between leaves. In addition, the number of variants within a leaf increases as a function of distance from the inoculated (source) leaf, suggesting that the circulating sap may serve as a continual source of virus. Notably, multiple mutational variants were observed in the cylindrical inclusion (CI) protein (known to be involved in both cell-to-cell and systemic movement of the virus) that were present in multiple (19/24) leaf samples. These mutations resulted in a conformational change, suggesting that they might confer a selective advantage in systemic movement within the vine. Overall, these data reveal that bottlenecks occur during systemic movement, that variants circulate in the phloem sap throughout the infection process, and that important conformational changes in CI protein may arise during individual infections.
authors.affiliation: Molecular and Computational Biology, University of Southern California, Los Angeles, CA, 90033, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Dunham
authors.affiliation: Seed Science Center, Iowa State University, Ames, IA 50011, USA.|Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: H E
authors.initials: HE
authors.lastname: Simmons
authors.affiliation: Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA.|Marie Bashir Institute for Emerging Diseases & Biosecurity, Charles Perkins Centre, School of Biological Sciences and Medical School, The University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: E C
authors.initials: EC
authors.lastname: Holmes
authors.affiliation: Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: A G
authors.initials: AG
authors.lastname: Stephenson
mesh_terms: D028464:Cucurbita / Q000821:virology*; D014644:Genetic Variation; D009154:Mutation; D010802:Phylogeny; D010935:Plant Diseases / Q000821:virology*; D018515:Plant Leaves / Q000821:virology; D017800:Potyvirus / Q000145:classification / Q000235:genetics* / Q000502:physiology
keywords: Cylindrical inclusion protein; Evolution; Intra-host genetic diversity; Systemic movement; Zucchini yellow mosaic virus
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