Alphasatellitidae: a new family with two subfamilies for the classification of geminivirus- and nanovirus-associated alphasatellites

International audienceNanoviruses and geminiviruses are circular, single stranded DNA viruses that infect many plant species around the world. Nanoviruses and certain geminiviruses that belong to the Begomovirus and Mastrevirus genera are associated with additional circular, single stranded DNA molecules (similar to 1-1.4 kb) that encode a replication-associated protein (Rep). These Rep-encoding satellite molecules are commonly referred to as alphasatellites and here we communicate the establishment of the family Alphasatellitidae to which these have been assigned. Within the Alphasatellitidae family two subfamilies, Geminialphasatellitinae and Nanoalphasatellitinae, have been established to respectively accommodate the geminivirus- and nanovirus-associated alphasatellites. Whereas the pairwise nucleotide sequence identity distribution of all the known geminialphasatellites (n = 628) displayed a troughs at similar to 70% and 88% pairwise identity, that of the known nanoalphasatellites (n = 54) had a troughs at similar to 67% and similar to 80% pairwise identity. We use these pairwise identity values as thresholds together with phylogenetic analyses to establish four genera and 43 species of geminialphasatellites and seven genera and 19 species of nanoalphasatellites. Furthermore, a divergent alphasatellite associated with coconut foliar decay disease is assigned to a species but not a subfamily as it likely represents a new alphasatellite subfamily that could be established once other closely related molecules are discovered

Further molecular characterization of weed-associated begomoviruses in Brazil with an emphasis on Sida spp Caracterização molecular adicional de begomovírus associados a plantas daninhas no Brasil, com ênfase em Sida spp

Begomoviruses are whitefly-transmitted, single-stranded DNA viruses that are often associated with weed plants. The aim of this study was to further characterize the diversity of begomoviruses infecting weeds (mostly Sida spp.) in Brazil. Total DNA was extracted from weed samples collected in Viçosa (Minas Gerais state) and in some municipalities of Alagoas state in 2009 and 2010. Viral genomes were amplified by RCA, cloned and sequenced. A total of 26 DNA-A clones were obtained. Sequence analysis indicated the presence of 10 begomoviruses. All viral isolates from Blainvillea rhomboidea belonged to the same species, Blainvillea yellow spot virus (BlYSV ), thereby suggesting that BlYSV may be the only begomovirus present in this weed species. Four isolates represent new species, for which the following names are proposed: Sida yellow blotch virus (SiYBV), Sida yellow net virus (SiYNV), Sida mottle Alagoas virus (SiMoAV) and Sida yellow mosaic Alagoas virus (SiYMAV). Recombination events were detected among the SiYBV isolates and in the SiYNV isolate. These results constitute further evidence of the high species diversity of begomoviruses in Sida spp. However, the role of this weed species as a source of begomoviruses infecting crop plants remains to be determined.<br>Begomovírus são vírus de DNA circular fita simples transmitidos por mosca branca, os quais são frequentemente associados com plantas daninhas. O objetivo deste trabalho foi caracterizar a diversidade de begomovírus infectando plantas daninhas (principalmente Sida spp.) no Brasil. DNA total foi extraído a partir de plantas daninhas coletadas em Viçosa (Minas Gerais) e em alguns municípios do estado de Alagoas em 2009 e 2010. Os genomas virais foram amplificados por RCA, clonados e sequenciados. Um total de 26 clones de DNA-A foram obtidos. A análise das sequências indicou a presença de dez diferentes begomovírus. Todos os isolados originários de Blainvillea rhomboidea pertencem a uma única espécie viral, Blainvillea yellow spot virus (BlYSV), sugerindo que o BlYSV pode ser o único begomovírus presente nesta espécie de planta invasora. Quatro isolados representam espécies novas, para as quais os seguintes nomes são propostos: Sida yellow blotch virus (SiYBV), Sida yellow net virus (SiYNV), Sida mottle Alagoas virus (SiMoAV) e Sida yellow mosaic Alagoas virus (SiYMAV). Eventos de recombinação foram detectados entre isolados de SiYBV e no isolado de SiYNV. Estes resultados constituem uma evidência adicional da alta diversidade de espécies de begomovírus em Sida spp. Contudo, o possível papel dessas plantas daninhas como fonte de begomovírus para plantas cultivadas ainda permanece indeterminado