Plants are continuously challenged by pathogens. To defend themselves against pathogenic microorganisms, plants possess an innate immune system, by which they are able to recognise invading pathogens and activate a cellular immune response. Receptor-like proteins (RLPs) and receptor-like kinases (RLKs) located on the plasma membrane (PM) are essential for resistance to pathogens. RLPs, such as Cf-4, lack a kinase domain and the RLK SUPPRESSOR of BIR1-1 (SOBIR1) is required for Cf-4-mediated resistance to Cladosporium fulvum that secretes the effector Avr4. The bimolecular complex Cf-4/SOBIR1 further recruits BRI1-ASSOCIATED KINASE 1 (BAK1) to trigger downstream signalling upon Avr4 perception. The identification of additional RLKs and/or receptor-like cytoplasmic kinases (RLCKs) interacting with the tripartite complex Cf-4/SOBIR1/BAK1, in addition to elucidation of the mechanism by which SOBIR1 and BAK1 activate each other upon recognition of Avr4, should lead to a better understanding of the natural resistance of plants to pathogens.