Comparative Pathogenomics From Six New Phytoplasma Genome Drafts

In view of the development of population pathogenomics for phytoplasmas, we optimized a procedure which allowed the reconstruction of high quality genome drafts fro Illumina reads, using standard nucleic acids preparation from periwinkle. The genome analysis of four phytoplasma strains belonging to the 16SrII group (X disease clade), namely the Vaccinium Witches' Broom phytoplasma (647,754 nts in 272 contigs), the Italian Clover Phyllody phytoplasma strain MA (597245 nts in 197 contigs), the Poinsettia branch-inducing phytoplasma strain JR, (631440 nts in 185 contigs), and the Milkweed Yellows phytoplasma (583806 nts in 158 contigs) revealed similarities in their basic metabolic potential with the genomes of other wide host range phytoplasmas, and highlighted the role of inward and outward trafficking through the phytoplasma cellular membrane in defining virulence and host adaptation. Genome analysis was also applied to compare two phytoplasmas related to "Ca. Phytoplasma asteris" and belonging to the 16SrI-B subgroup, namely the Chrysanthemum yellows phytoplasma (660013 nts in 253 contigs) and the Lettuce yellows phytoplasma (694813 nts in 205 contigs). The results obtained showed that, despite the strikingly different symptoms induced in the infected periwinkle, the two phytoplasmas share highly similar genomes. Moreover, the results of the genome sequencing of the six phytoplasmas pointed out the significant role of horizontal gene transfer among different "Ca. Phytoplasma" species in shaping phytoplasma genomes and promoting their diversity.