NUCLEOTIDE SEQUENCE VARIATIONS IN THE HSP70 GENE OF OLIVE LEAF YELLOWINGASSOCIATED VIRUS
S. Essakhi, T. Elbeaino, M. Digiaro, M. Saponari, G.P. Martelli
Single strand conformation pattern (SSCP) analysis of the HSP70 homologue gene of thirty isolates of Olive leaf yellowing-associated virus (OLYaV) from different geographical origins showed the existence of wide variability within this virus. This variability was clearly confirmed when multiple alignments of the HSP70 nucleotide sequences of 13 isolates that had different SSCP patterns were analysed. All isolates clustered with OLYaV-type in a phylogenetic tree constructed with the available HSP70 sequences of several members of the family Closteroviridae. The level of variability in a fragment of 383 nucleotides of the HSP70 gene ranged from 1% to 23%. Three distinct groups of isolates were identified, each of which had an internal variability lower than 10%, but showed a higher divergence from members of the other two groups (from 15 to 23%). In RT-PCR assays, primers specific for HSP70, but not those specific for the RdRp or HSP90 cistrons, amplified isolates of all groups. Whether or not the molecular differences observed in a highly conserved portion of the Closteroviridae genome (HSP70) can be indicative of the existence of more than one species within the OLYaV population remains to be ascertained.