SecY gene sequence analysis for finer differentiation of diverse strains in the aster yellows phytoplasma group.

Aster yellows (AY) group (16SrI) phytoplasmas are associated with more than 100 economically important diseases worldwide and represent the most diverse and widespread phytoplasma group. Phylogenetic analysis of secY gene sequences resolved 10 genetically distinct lineages. The 10 lineages coincide with those delineated by phylogenetic analysis based on ribosomal protein (rp) gene sequences. However, greater genetic variability among the 10 lineages was revealed based on secY gene sequences. The distinct phylogenetic lineages can be readily identified through restriction fragment length polymorphism (RFLP) analysis of secY gene sequences. Ten subgroups were differentiated among the AY group phytoplasmas based on RFLP analysis of secY gene sequences. Phylogenetic analysis based on secY gene sequences in this study, and previous studies on the 16S rRNA gene, tuf gene, and rp gene sequences reinforced the notion that most subgroups identified by RFLP analysis of secY and rp gene sequences represent distinct phylogenetic lineages.