Characterization of candidate effectors of “flavescence dorée” phytoplasma: expression and subcellular localization

“Flavescence doree” is a severe disease of grapevine that expands across Europe. The associated agent is a phytoplasma belonging to ribosomal group 16SrV, and transmitted in the field by the insect vector Scaphoideus titanus. Genome sequence analysis of the “flavescence doree” phytoplasma allowed to define a restricted set of 12 putatively secreted proteins of unknown function. In order to provide a first characterization of these candidate effectors, their expression level was determined both in host plants and insect vectors. The results indicated variable expression levels among candidates, with differential transcript accumulation between plant and insect hosts. The subcellular localizations of the candidate effectors were determined in both plant and insect cells by fusion with a fluorescent protein and compared. All but one candidate displayed a similar pattern in plant and insect cells. In total, this study provides a first glimpse of “flavescence doree” phytoplasma candidate effectors, and builds a foundation for a deeper understanding of the virulence mechanisms deployed by this phytoplasma.