The complete genome sequence of the BD variant of grapevine leafroll-associated virus 2

Excerpt

Grapevine leafroll-associated virus 2 (GLRaV-2), a member of the genus Closterovirus, is the causal agent of leafroll and graft incompatibility in grapevine [4, 7, 10, 12, 13]. Four complete genomic nucleotide sequences of GLRaV-2 isolates have been reported: PN and OR1 from the USA [8, 14], RG from California [13] and 93/955 from South Africa [11]. The sequences reported for PN and OR1 are almost identical (99.6% nt identity) and have 90% nt identity with 93/955, whereas the RG sequence is the most divergent (73% nt identity with PN). Analysis of Italian grapevine samples revealed a new GLRaV-2 isolate called BD. It reacted with a GLRaV-2 antiserum but was not amplified by RT-PCR using GLRaV-2-specific primers [3]. A study of the genetic variability of the coat protein (CP) region showed that BD is one of the most divergent GLRaV-2 isolates, differing from PN and RG by about 25% in its nucleotide sequence [4]. Moreover, the BD isolate is a mild GLRaV-2 variant, because, in contrast to the PN and RG isolates, it is not associated with graft incompatibility, and it rarely induces leafroll symptoms [4, 12, 13]. The apparent distinctness of the BD isolate and the scarcity of complete GLRaV-2 genome sequences prompted us to molecularly characterize the genome of the BD variant and compare the results with published information, thereby allowing future mapping of the genome regions involved in the expression of different symptoms. …