Abstract
We have performed a systematic search for recombination in the region encoding coat protein and the 3' non-translated region in natural isolates of potyviruses, the largest group of plant RNA viruses. The presence of recombination, and the localization of the cross-over points, were confirmed statistically, by three different methods. Recombination was detected or suspected in 18 out of 109 potyvirus isolates tested, belonging to four out of eight virus species, and was most prevalent in potato virus Y, clear in bean common mosaic virus, and possible in bean yellow mosaic and zucchini yellow mosaic viruses. Recombination was not detected in the four other potyvirus species tested, including plum pox virus, despite the availability of numerous sequences for this last species. Though it was not specifically researched, no evidence for inter-specific recombination was found. For several reasons, including the fact that only a minor portion of the genome was analysed, the above figures certainly represent an underestimate of the extent of recombination among isolates of potyviruses, which might thus be a common phenomenon.
Highlights
There is growing evidence that RNA recombination is a major evolutionary factor in plant RNA viruses (Koonin, 1991; Simon & Bujarski, 1994)
We demonstrate the occurrence of recombination in the region encoding the capsid protein (CP) and in the 3' non-translated region (3'NTR) of several isolates of potato virus Y (PVY) and bean common mosaic virus (BCMV)
We first focused on PVY, since this virus is of considerable economic importance which has prompted more studies than on other potyviruses, resulting in a large dataset
Summary
There is growing evidence that RNA recombination is a major evolutionary factor in plant RNA viruses (Koonin, 1991; Simon & Bujarski, 1994). The potyvirus group is well suited for such a search for several reasons It is the largest genus of plant viruses (Ward & Shukla, 1991), with many members partially or fully sequenced. RNA recombination is known to be possible in this genus: it has been described between field isolates of plum pox virus (Cervera et al, 1993) and may have occurred between an isolate of turnip mosaic virus and a cellular sequence (Sano et al, 1992). The results obtained may be confirmed by various statistical means Using this approach, we demonstrate the occurrence of recombination in the region encoding the capsid protein (CP) and in the 3' non-translated region (3'NTR) of several isolates of potato virus Y (PVY) and bean common mosaic virus (BCMV). Potential recombinants were observed for bean yellow mosaic virus (BYMV) and zucchini yellow mosaic virus (ZYMV), but apparently not for watermelon virus II (WMV2), turnip mosaic virus (TuMV), plum pox virus (PPV) and papaya ringspot virus (PRSV)
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