Viruses Genomes - DROSOPHILA C VIRUS

Drosophila C virus (DCV) is a small, RNA-containing virus. DCV has historically been classified as an ungrouped member of the virus family Picornaviridae . DCV has a number of picornavirus-like characteristics including its size, sedimentary coefficient, buoyant ensity, the number and size of their structural proteins and polyadenylated genomic RNA with a small protein (VPg) attached to the 5' end of the sequence. The newly available genome sequence now shows organization different to that of other RNA virus families whose sequences are known. The single-stranded positive-sense genomic RNA is 9264 nucleotides in length and contains two large open reading frames (ORFs) which are separated by 191 nucleotides. The finding of this novel genome organization for DCV shows that this virus is not a member of the Picornaviridae as previously thought, but belongs to a distinct and hitherto unrecognised virus family.

Some Drosophila melanogaster populations are naturally infected by DCV. It was first discovered in a French strain called Charolles in 1972 and has since been detected from geographically isolated natural populations of D. melanogaster that seemed healthy. The virus, transmitted by feeding is almost nonpathogenic. However, the DCV extracted from the Charolles strain (Dmc) does affect the reproductive capacity of its hosts. Naturally infected flies and flies experimentally infected by feeding have a bigger reproductive potential than their uninfected counterparts.

The DCV, increases the allocation of resources devoted to reproduction in its Drosophila hosts. DCV, contaminated flies develop more rapidly than healthy ones of the same genotype; females are heavier, have a greater number of functional ovarioles and produce more eggs and more offspring. However, experimental study of DCV virulence showed that the virus is extremely pathogenic when injected into adult reference flies, these dying within 3 or 4 days after the injection.

Considerable research has been undertaken and in all cases in vivo infected flies have characteristics that could be advantageous in the proper environment. If this proves to be true, this would be the first time that viruses appeared to have a beneficial effect. If naturally infected populations have greater fitness because of the DCV influence on some of the metric characters, particularly on developmental time and mean number of ovarioles, it would be possible to understand why DCV was maintained in natural populations.

References:

http://www.genetics.org/cgi/reprint/140/4/1289
http://www.genetics.org/cgi/reprint/107/4/635