New insights on begomoviruses: Virus-virus interactions in mixed infections and estima- tion of genetic bottlenecks during vector transmission

• Ano de defesa: 2023
• Autor(a) principal: Barbosa, Tarsiane Mara Carneiro
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa; Bioquímica Aplicada
• Palavras-chave em Português: Geminivírus; Vírus de plantas; Mosca-branca; Biologia Molecular
• Link de acesso: https://locus.ufv.br//handle/123456789/31606; https://doi.org/10.47328/ufvbbt.2023.224

Yield losses in tomato crops caused by a begomovirus complex are observed in all the main producing regions of Brazil. In this work, aspects related to interactions in mixed infection and genetic bottlenecks during transmission by the insect vector were explored. Previous studies revealed a complex interaction between the begomoviruses tomato rugose mosaic virus (ToRMV) and tomato severe rugose virus (ToSRV), in which ToRMV negatively interferes with ToSRV infectivity and accumulation. Differences in the Rep protein and in the common region (CR) sequence may be involved in the preferential replication of ToRMV components during mixed infection. Thus, we used previously constructed clones for ToSRV DNA-A con- taining the same nucleotides that occur in ToRMV at divergent positions in the CR and IRD domain of the Rep protein. ToSRV infectivity and viral accumulation in single infection were not affected by any of the nucleotide changes. In a mixed infection with ToRMV and ToSRV- A (ToR:CR) , high infectivity and DNA accumulation of ToSRV (ToR:CR) , similar to wild-type ToSRV, were observed. This was not the case when plants were inoculated with ToRMV and ToSRV-A (ToR:IRD) . These results suggest that CR nucleotides act as specific recognition sites for Rep binding, increasing the rate of viral replication and viral DNA accumulation. The emer- gence of begomoviruses over the last few decades is related to the worldwide spread of white- flies of the Bemisia tabaci complex. Although vector transmission is considered an important genetic bottleneck for plant viruses, few studies have attempted to estimate its magnitude. To assess the occurrence and magnitude of genetic bottlenecks during vector transmission of be- gomoviruses, B. tabaci Middle East-Asia Minor 1 (MEAM1) was subjected to acquisition pe- riods of 24 h and 48 h in tomato plants and Euphorbia heterophylla infected by ToSRV and Euphorbia yellow mosaic virus (EuYMV), respectively. The insects were collected and dis- sected to obtain the midgut (MG) and salivary glands (SG). Total DNA of each organ was extracted, enriched through RCA and sequenced. A larger number of sequence reads mapped to EuYMV and ToSRV reference genomes in the MG sample compared to SG samples, con- sistent with the higher viral load in the MG reported in the literature. The analysis of SNPs indicated a significant number of deletions in the EuYMV MG sample and a high number of nucleotide substitutions in the SG samples. Estimates of Shannon's entropy also indicated a greater degree of genetic variability of the SG samples. Our results suggest that the midgut imposes a genetic bottleneck in B. tabaci MEAM1, but that the genetic variability of the viral population is restored during passage through the salivary glands. Keywords: Geminivirus. Plant Virus. Whitefly