L'evolution des virus a ARN: roles de la selection et de la derive genetique

RNA viruses, retroviruses and pararetroviruses, are known for their rapid evolution, because of high mutation rates and short generation times. Replication errors (mutations and imperfect recombinations) generate a great variability. However, selection pressures shape viral populations diversity, by acting at different steps of virus infectious cycle : strategies of genome expression, interactions with host(s) and vector(s) are the targets of selection. Such a selection sorts out genotypes according to their fitness. The second most important parameter acting on viral population diversity, genetic drift, occurs when population effective size is low, which seems to be frequent during host or tissue infection initiation. By contrast to selection, drift is a random, fitness‐independent process, which may lead to the fixation of deleterious mutations. Despite their exceptionally high mutation rates, RNA viruses seem to follow classical population genetics principles, as showed during the last two decades.http://www.john-libbey-eurotext.fr/en/revues/bio_rech/vir/e-docs/00/04/04/91/resume.md?type=text.htm

The passage of potato leafroll virus through Myzus persicae gut membrane regulates transmission efficiency.

Potato leafroll virus (PLRV) is transmitted by aphids in a persistent manner. Although virus circulation within the aphid leading to transmission has been well characterized, the mechanisms involved in virus recognition at aphid membranes are still poorly understood. One isolate in our collection (PLRV-14.2) has been shown to be non- or only poorly transmitted by some clones of aphids belonging to the Myzus persicae complex. To determine where the transmission process was blocked within the aphid, three virus transmission procedures were used. PLRV-14.2 could not be transmitted, or was only very poorly transmitted, after acquisition from infected plants or from purified preparations. In contrast, it could be transmitted with more than 70% efficiency when microinjected. Therefore, it is concluded that the gut membrane was a barrier regulating passage of PLRV particles from the gut lumen into the haemocoel of M. persicae. Comparison of coat protein (CP) and readthrough protein (RTP) sequences between poorly and readily transmissible isolates showed that PLRV-14.2 differed from other PLRV isolates by amino acid changes in both of these proteins. It is hypothesized that at least some of the changes found in CP and/or RTP reduced virus recognition by aphid gut receptors, resulting in reduced acquisition and subsequent transmission of PLRV-14.2.J. Rouzé-Jouan, L. Terradot, F. Pasquer, S. Tanguy, and D. Giblot Ducray-Bourdi