PHYLOGENETIC ANALYSIS OF TRIPLE GENE BLOCK VIRUSES BASED ON THE TGB-1HOMOLOG GENE INDICATES A CONVERGENT EVOLUTION

The complete nucleotide sequence of the triple gene block one (TGB 1) of cymbidium mosaic potexvirus (CymMV) was compared to those from othe r potex-, carla-, furo- and hordeiviruses. Seven conserved motifs in t he TGB 1, including the ATP-GTP binding domain (P-Loop) consensus GXXG KTSTS, were found in all four virus genera. We propose that all TGBV c an be classified into phylogenetic clusters based on their TGB I homol og genes. These clusters can be further delineated to form subgroups. The first cluster comprises the potexviruses which are further subdivi ded into three subgroups; BaMV, FMV, PlaMV and PapMV (subgroup Ia); Cy mMV, PAMV, NMV, SMYEaV and WCIMV (subgroup Ib) and PVX (subgroup Ic). The second cluster comprises carlaviruses with a dual subgrouping; CVB , LSV, PVM, PMV and ASPV (subgroup IIa) and LVX (subgroup IIb). The th ird cluster carries the most diverse of TGBV comprising furoviruses PC V, PMTV and BSBV (subgroup IIIa) and hordeiviruses PSLV, BSMV and LRSV (subgroup IIIb). The phylogenetic relationships of triple gene block viruses (TGBV) based on the TGB I homolog gene indicates a convergent evolution.