The possible BSV and banana evolution story

Banana streak viruses (BSVs) are double stranded DNA pararetroviruses belonging to the family Caulimoviridae, genus Badnavirus, with no integration step in their life cycle. They are responsible for mosaic streak disease on banana. The banana genome (Musa sp.) is invaded by numerous badnavirus sequences. The majority of viral integrants is mostly defective as a result of pseudogenisation driven by the host genome evolution. Conversely, only some endogenous BSV (eBSVs) can release a functional BSV genome following stresses. The other ones are so-called BSV-like because episomal particles corresponding to the integrated counterparts have not been identified so far. All the badnaviral sequences described so far [1] are spread among the three main groups of the badnavirus diversity [2]. We established that eBSVs belong to the group 1 of the badnavirus diversity and are present in Musa balbisiana (B) genomes only [3;4]. We elucidated their sequence and organization for three BSV species (BSOLV, BSGFV and BSImV) present within the B genome of the seedy diploid PKW. We developed several PCR and deCAPS markers for eBSV genotyping [3-5]. In addition, we began the characterization of BSV-like sequences diversity only belonging to group 2 using Southern blot and PCR with primers and probes specific of the 7 BSV-like species identified so far in this group [2] and of the new species identified in the M. acuminata (A) doubled-haploid Pahang genotype recently sequenced [6]. We then retraced the evolutionary BSV and banana stories by the study of PKW-related eBSV and BSV-like sequences among the Musa diversity. The data suggest that eBSV occurred after the M. acuminata/M. balbisiana speciation and before the M. balbisiana diversification. The BSVlike integrations likely occurred for some of them before the M. acuminata/M. balbisiana speciation whereas others occurred afterwards. All together our data allowed us to propose an evolutionary scheme of BSV/eBSV banana evolution. (Résumé d'auteur