Begomoviruses: variability, evolution, and interactions with hosts and vectors

• Ano de defesa: 2019
• Autor(a) principal: Xavier, César Augusto Diniz
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Begomovírus; DNA de forma B; Deaminação; Diversidade genética; Mosca-branca; Fitopatologia
• Link de acesso: https://locus.ufv.br//handle/123456789/27417

Begomoviruses constitute an important group of plant pathogens being widespread in the world. Although New World begomoviruses are predominantly bipartite, the bipartite nature of these viruses has been little explored in terms of their evolutionary significance. We performed a parallel evolutionary analysis of the DNA-A and DNA-B components of New World begomoviruses from cultivated and non-cultivated hosts. The two components respond differentially to evolutionary process, with the DNA-B being more variable and more prone to recombination than the DNA-A. Our results indicate an interplay between reassortment and recombination acting at different levels across distinct subpopulations and genomic components. This more relaxed evolution may be an advantage of multipartition, as each component may behave as a single almost independent evolutionary entity, allowing a faster adaptation to an ever-changing environment. Furthermore, begomovirus population present a high level of genetic variability. Interestingly, a mutational bias has been detected in begomovirus genomes, favoring C to T transitions, suggesting that cytidine deamination may act on these viruses. We investigated a possible role of A. thaliana cytidine deaminase (AtCDA and AtCDAL4) as components of plant antiviral immunity. We demonstrate distinct functional roles for AtCDAs upon begomovirus infection. While AtCDA has a proviral effect during Cabbage leaf curl virus infection, AtCDAL4 has antiviral activity, constituting a putative branch of antiviral immune response in plants. However, unlike in animals, our results suggest that AtCDAs affect viral infection independently of deaminase activity. We also studied factors underlying leading to emergence and the current patterns of prevalence of begomoviruses in tomato by quantifying the replicative and transmission fitness of two begomoviruses infecting tomato in Brazil, Tomato severe rugose virus (ToSRV) and Tomato yellow spot virus (ToYSV). Interestingly, despite ToYSV is not widespread in the field, it presented similar replicative fitness compared to ToSRV, a widespread begomovirus, in tomato. These results suggest that adaptation to the host does not explain the prevalence of ToSRV over ToYSV, as both viruses presented similar adaptation levels as evaluated here. However, while ToSRV was transmitted by B. tabaci MEAM1 and MED, ToYSV was not transmitted by them, reason by which this virus probably is not spread in the field. Finally, it has been hypothesized that the absence of a competent vector that efficiently colonizes cassava is the reason why begomoviruses have not emerged in South America. To test this hypothesis, we performed a country-wide whitefly diversity study in cassava in Brazil. A high degree of species richness was observed, with five previously described species and two putative new ones. The most prevalent species were Tetraleurodes acaciae and Bemisia tuberculata, representing over 75% of the analyzed individuals. Although we detected, for the first time, the presence of whitefly species of the Bemisia tabaci complex colonizing cassava in Brazil, they were not prevalent. Our results indicate an ongoing adaptation process of B. tabaci Middle East-Asia Minor 1 to cassava, increasing the likelihood of begomovirus emergence in this crop in the future. The results obtained here, expand our knowledge about the wide spectrum of interactions among begomoviruses-hosts-vectors. Keywords: DNA-B. Base deamination. Whitefly diversity.