All source data from the referenced paper (Figures 1b and Table 1). 22 Excel files of data from each experimental block of the reactive oxygen species assay, 1 Excel file of the combined data from the bacterial growth enhancement assay, 1 Excel file of the RT-qPCR data.

Parasitic plants are the primary biotic constraint in many crop production systems. The most agriculturally devastating parasitic plants, including witchweeds (Striga spp.) and broomrapes (Phelipanche and Orobanche spp.), are in the Orobanchaceae family. Phelipanche aegyptiaca is an obligate holoparasite that lacks the capacity for photosynthesis and therefore relies on host parasitization for acquisition of all nutrients. P. aegyptiaca is a broad host range pathogen with the ability to parasitize diverse dicot hosts through attachment and development of a feeding structure known as a haustorium. The mechanisms P. aegyptiaca and other parasitic plants employ to avoid host plant immunity and form successful haustorial attachments are unknown. Here, we demonstrate that P. aegyptiaca actively suppresses salicylic acid-mediated immunity of the host plant Arabidopsis thaliana. We hypothesized that parasitic plants may deploy immunity-suppressing effector proteins through the haustorial interface to subvert host plant immune responses. We devised a pipeline to select and clone 27 candidate secreted effector proteins in P. aegyptiaca and tested these proteins for the potential to suppress known plant immunity pathways. Five candidate effectors suppressed flg22-elicited production of reactive oxygen species when transiently expressed in Nicotiana benthamiana. We propose that two of these candidate effectors function through interfering with pattern triggered immunity using molecular mimicry.