constraints to genetic exchange support gene coadaptation in a tripartite rna virus限制基因交换支持三方rna病毒基因相互适应.pdfVIP

Constraints to Genetic Exchange Support Gene Coadaptation in a Tripartite RNA Virus 1¤ 1,2 ´ 1,2* Fernando Escriu , Aurora Fraile , Fernando Garcıa-Arenal ´ ´ ´ ´ ´ 1 Departamento de Biotecnologıa, Universidad Politecnica de Madrid, Madrid, Spain, 2 Centro de Biotecnologıa y Genomica de Plantas, Universidad Politecnica de Madrid, Madrid, Spain Genetic exchange by recombination, or reassortment of genomic segments, has been shown to be an important process in RNA virus evolution, resulting often in important phenotypic changes affecting host range and virulence. However, data from numerous systems indicate that reassortant or recombinant genotypes could be selected against in virus populations and suggest that there is coadaptation among viral genes. Little is known about the factors affecting the frequency of reassortants and recombinants along the virus life cycle. We have explored this issue by estimating the frequency of reassortant and recombinant genotypes in experimental populations of Cucumber mosaic virus derived from mixed infections with four different pairs of isolates that differed in about 12% of their nucleotide sequence. Genetic composition of progeny populations were analyzed at various steps of the virus life cycle during host colonization: infection of leaf cells, cell-to-cell movement within the inoculated leaf, encapsidation of progeny genomes, and systemic movement to upper noninoculated leaves. Results indicated that reassortant frequencies do not correspond to random expectations and that selection oper