Questions and Concepts in Plant Virus Evolution: a Historical Perspective

Abstract

The interest in plant virus evolution can be dated to the late 1920s, when it was shown that plant virus populations were genetically heterogeneous, and that their composition changed according to the experimental conditions. Many important ideas were generated prior to the era of molecular virology, such as the role of hostand vector-associated selection in virus evolution, and also that small populations, gene coadaptation and evolutionary trade-offs could limit the efficiency of selection. The analysis of viral genomes in the 1980s and 1990s established the quasispecieslike sU'ucture of then populations and allowed extensive analyses of the relationships among virus strains and species. The concept that virus populations had huge sizes and high rates of adaptive mutations became prevalent in this period, with selection mostly invoked as explaining observed patterns of population structure and evolution. In recent times virus evolution has been coming into line with evolutionary biology, and a more complex scenario has emerged. Population bottlenecks during host colonization, during host-to-host transmission or during host population fluctuations may result in smaller population sizes, and genetic drift has been recognized as an important evolutionary factor. Also, particularities of viral genomes such as low levels of neutrality, inultifunctionality of coding and encoded sequences or strong epistasis could constrain the plasticity of viral genomes and hinder then response to selection. Exploring the complexities of plant virus evolution will continue to be a challenge for the future, particularly as it affects host, vector and ecosystem dynamics.

Populations of Genomic RNAs Devoted to the Replication or Spread of a Bipartite Plant Virus Differ in Genetic Structure

“…Our results have shown uneven distributions of mutations in the four genomic regions analyzed, strongly suggesting that representative regions of the viral genome should be considered to obtain rigorous estimates of mutation frequencies and genetic distances between sequences within mutant clouds. The need for analysis of several genomic regions has also been emphasized in previous studies of the variability of animal and plant RNA viruses (1,18,33). Some genomic regions of plant viruses can exhibit extremely low variation (48) and give an erroneous idea of virus genetic variability.…”

Caracterización molecular y desarrollo de métodos de diagnóstico del género Fabavirus Evaluación de BTH como método de control

“…El efecto de este proceso es muy importante en casos de reducción drástica de la población viral (cuellos de botella) que pueden estar asociados al movimiento del virus entre células de la planta o en la transmisión a nuevos huéspedes (Sacristán et al, 2003;Li & Roossinck, 2004;Ali et al, 2006;García-Arenal & Fraile, 2008). El flujo genético dentro y entre poblaciones virales uniformiza la distribución de la estructura genética, de manera que cuando las tasa de migración es baja se favorece la divergencia entre poblaciones.…”

“…También se han detectado fenómenos de recombinación entre especies virales (White & Morris, 1995;Monci et al, 2002;Lefeuvre et al, 2007;García-Arenal & Fraile, 2008). Se ha propuesto que la recombinación podría ser ventajosa para los virus de RNA.…”