Arbuscular mycorrhizal (AM) fungi form mutualistic associations with more than 80% of all land plants. This symbiotic interaction is established by a strict controlled exchange of signals whereby the fungus also needs to repress the plant’s defense response. From the plant pathology field, we know that this is achieved by the secretion of small effector proteins. Interestingly, AM fungi are also known to secrete effectors but little is known about their role inside the plant. In our research proposal, we will advance the state-of-the-art about how these AM effectors act, by identifying with which plant proteins they interact and how this interaction alters plant growth during mycorrhization. Here, we will focus on Rhizophagus irregularis with its host tomato. First, we will identify an interaction network between fungal effectors and tomato proteins via high-throughput analyses of direct interactions by Y2H-Seq. After verification of the interactions with conventional assays, we will use the innovative proteomics technique BioID to further fine tune and validate the obtained interactome. Finally, we will study the role of three main tomato root proteins in reprogramming plant growth using a multidisciplinary approach combining phenotyping with molecular, physiological and biochemical assays. Our findings will benefit the current international interest in AM fungal effector biology as well as the tomato research community by providing novel insights in tomato interactomics.