Proposal to establish a common taxon for 16SrV-C and 16SrV-D phytoplasmas and three genetic clades based on combined 16S rDNA signatures and variability of housekeeping genes

Members of subgroups 16SrV-C and-D form a homogenous genetic cluster with a complex ecology that involves perennial plants such as alders, grapevine and Clematis and leafhopper vectors. However, despite the monophyletic origin of the members of these subgroups, a common specific sequence could not be found in their 16S rRNA gene, preventing from describing a common taxon according to the rules for the description of ‘Candidatus Phytoplasma’ species. The genetic diversity of 16S rRNA and five housekeeping genes among European and American strains of 16SrV phytoplasmas, including 16SrV-C strains detected in Canadian alders were examined. Members of subgroups 16SrV-C and 16SrV-D share a common combination of three sequence signatures in the 16S rRNA gene that can serve as descriptors for a new common taxon. According to the sequences of tuf, rplV-rpsC, rplF-rplR, map and uvrB-degV genes, they can be divided into three genetic clusters.