PM19_00185 of ‘Candidatus Phytoplasma mali’ is a protein that functions as a E3 ubiquitin ligase

Phytoplasmas are the agents associated with numerous diseases in several plant species all over the world, including important food crops. The mode of phytoplasma infection is poorly understood and often based on genomic data. A yeast two-hybrid screening was used to find new protein-protein interactions between ‘Candidatus Phytoplasma mali’, the phytoplasma associated with apple proliferation and its host plant. ‘Ca. P. mali’ strain PM19 genome encodes a protein PM19_00185 that interacts with at least five different ubiquitin conjugating enzymes (UBC, E2) of Arabidopsis thaliana. The in vitro ubiquitination assay shows that PM19_00185 is enzymatically active as E3 ligase with A. thaliana E2 UBC09.