Comparison of phytoplasma effector-flanking genomic regions indicates potential mobile units as a driving force of horizontal transfer of symptom-determinant genes

Phyllody is a characteristic symptom caused by phytoplasmas, a group of obligate intracellular plant pathogenic bacteria, retaining a phyllody-inducing effector gene family, phyllogen. Previous reports suggested the occurrence of horizontal gene transfer (HGT) of phyllogen among phytoplasma species and strains based on a phylogenetic comparison between phyllogen and 16S rRNA genes. However, the detailed mechanisms and evolutional process for HGT of phyllogen have been obscure. Here, we analyzed syntenic relationships on phyllogen-flanking genomic regions of 18 phytoplasma strains related to seven 'Candidatus' species.