Evolution of a DNA virus in the natural environment - a journey through time

• Ano de defesa: 2020
• Autor(a) principal: Silva, João Paulo da
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa; Fitopatologia
• Palavras-chave em Português: Vírus de plantas; Evolução; Diversidade genética; Begomovirus; Fitopatologia
• Link de acesso: https://locus.ufv.br//handle/123456789/30066

Viruses are recognized for having high mutation rates, resulting in rapid diversification and increased adaptive potential. For this reason, viruses are interesting models for evolutionary studies. Begomoviruses (family Geminiviridae) have a genome composed of one or two molecules of circular, single-stranded DNA (ssDNA) encapsulated in twinned icosahedral particles, and are transmitted by whiteflies of the Bemisia tabaci species complex. Begomoviruses cause diseases in several economically important crops. A great diversity of begomoviruses is present in non-cultivated hosts. Non-cultivated hosts play an important ecological and epidemiological role as reservoirs of viral biodiversity, as a source of primary inoculum, and as favorable environments for recombination, favoring the emergence of new species or variants. Begomovirus populations have a high degree of genetic variability, with mutation rates that are equivalent to those of RNA viruses. Although a number of studies have addressed the temporal dynamics of begomoviruses, these studies were conducted in large areas and in the context of agricultural environments. Little is known about the evolutionary dynamics of these populations in small scale and in natural environments. In this work. the variability and genetic structure of the begomovirus community in plants of Sida acuta (Malvaceae) was evaluated over a period of eight years. Samples were collected from 2011 to 2018 in an area of approximately 0.1 ha in Viçosa, MG. Three species were detected: Oxalis yellow vein virus (OxYVV), Sida yellow leaf curl virus (SiYLCV), and Sida micrantha mosaic virus (SimMV). The OxYVV and SiYLCV populations are subdivided into three well defined variants. In addition, we found two distinct strains of SimMV. These results highlight the heterogeneity of the begomovirus community, which coexist as a complex of different species and variants, and reveal the important ecological role of S. acuta, which constitutes a natural, highly permissive host for begomoviruses. The large fluctuation in the distribution of OxYVV variants over time reflects the adaptive differential of each variant and the impact of selection on viral populations in natural ecosystems. In addition, the data suggests that recombination between OxYVV variants was important to alleviate the impact of harmful mutations. The absence of a temporal signal in phylogenetic analyses suggests that the viral populations evolve at slow rates in natural environments, contrary to what has been observed in studies carried out in cultivated area subjected to anthropic disturbances. We hypothesize that, in crop systems, genetic drift is the predominat evolutionary mechanism responsible for patterns of segregation over time. Keywords: Evolution. Genetic diversity of Begomovirus. Temporal analysis.