Grapevine Leafroll Associated Virus ((GLRaV) Types 4 and 6, Molecular Characterization, Biological study, and RT-PCR Detection

More than 40%of the entire viral genome of Grapevine leafroll associated virus
(GLRaV) type 4 (total of about 4800 nucleotide (nt)) containing five open reading frames
(ORF or gene) and 50%of GLRaV-6 (6020 nt) including 5 complete ORFs and partial
ORF1b have been sequenced. The sequenced ORFs from 5′->3′ direction included: p5,
HSP70-homologue, p60, CP (coat protein) and p23. In addition, 975 nt sequences of the
3? end of ORF1b from GLRaV-6 also has been sequenced. Among the sequenced OFRs,
HSP70 is a more conserved gene, composed of 1602 nt which encodes for a protein
molecule of 533 amino acids long. ORF5 encodes for viral CP and in GLRaV-4 includes
819 nt of 272 aminoacids with a molecular weight of 29.5 kDa and in GLRaV-6 includes
810 nt of 269 aminoacids with a molecular weight of 29.2 kDa. The sequence
information revealed that these two viruses are closely related to each other. They have
81%aminoacid sequence similarities at the CP region and 78%at the HSP70 region. The
phylogenetic analysis using the CP nucleotide sequences of these two viruses compared
with other viruses in the family Closteroviridae (the family includes all other known
leafroll associated viruses) showed that these two viruses have closer relationship to
GLRaV-5 and -9. PCR detection primers have been designed and their evaluation is in