P-155 - Sweet but P-sycho: A novel Type III Effector Protein, with putative Glucosyltransferase and Kinase Domains, is enriched in Pseudomonas syringae PG2d isolated mainly from Prunus avium

Type III Effector proteins (T3E) are major virulence factors in the phytopathogen Pseudomonas syringae pv. syringae (Pss). They are translocated into the host cell through the type III secretion system (T3SS) to suppress plant immunity and enhance bacterial proliferation in susceptible plants. Some T3E have enzymatic activity, which target plant molecules within various plant cellular compartments. The sweet cherry pathogen Pss 9644 harbours T3E genes with unknown function. Here we show that a pathogenicity islet, harbouring contiguous hopBE1 and an uncharacterised effector, is enriched in Pss strains isolated from Prunus sp. A hrp-box promoter was identified upstream of hopBE1 driving transcription of both genes. The uncharacterised effector is structurally homologous to the animal pathogen toxin TcdA. It is a novel T3E with a putative glucosyltransferase and a kinase domain. To see if HopBE1 and TcdA are both functioning T3E, we expressed them as recombinant proteins in Pseudomonas. Both were induced in minimal media, but we only observed the secretion of TcdA in a T3S-dependent manner. Expression of hopBE1-tcdA in effectorless Ps pv. tomato D28E induces chlorosis in Arabidopsis thaliana leaves, associating this pathogenicity islet with a strong virulence activity.Future enzymatic activity assays and subcellular localization experiments will be used to functionally characterise TcdA with the aim to understand how it supports Pss growth and disease causation in sweet cherry.