The 124202 candidate effector of Melampsora larici-populina interacts with membranes in Nicotiana and Arabidopsis

Melampsora larici-populina (Mlp) is a parasitic fungus causing poplar leaf rust, a disease that threatens poplar plantations worldwide. Like other phytopathogens, Mlp translocates specialized proteins, called effectors, into host tissues and cells to eventually divert host resources. 124202 is a hypothetical Mlp effector selected through an in silico secretome analysis. It shares about 30% identity with the M. lini AvrM effector. Using heterologous systems, the objectives of this work were to assess if 124202 could mitigate Arabidopsis defence or potentiate Pseudomonas virulence and investigate its putative interaction partners in plants. Yeast two-hybrid screens identified three potential 124202 interactors in plants: lipoxygenase 2, synaptotagmin A and quinolinate synthase. Expression of a fluorescently tagged 124202 protein in Nicotiana benthamiana and Arabidopsis thaliana showed that it could be associated with membranes but may also be found in the cytoplasm of host cells. Bacterial infection assays in wild-type and 124202-expressing Arabidopsis lines indicate that 124202 does not alter the susceptibility of Arabidopsis to Pseudomonas syringae pv. tomato DC3000. Overall, our results suggest that the function of 124202 might involve vesicle-mediated trafficking but is unlikely to quantifiably contribute to the suppression of plant immunity.