Plants perceive pathogen-associated molecular patterns (PAMPs) via pattern recognition receptors (PRRs), leading to PAMP-triggered immunity (PTI). The Arabidopsis thaliana leucine-rich repeat receptor kinases FLS2 and EFR are amongst the best-characterized plant PRRs. Ligand-binding triggers the instantaneous association between FLS2/EFR and the LRR-RK BAK1 that acts as a co-receptor, leading to trans-phosphorylation between these proteins. Direct substrates for the FLS2/EFR-BAK1 complexes are cytoplasmic kinases, such as BIK1. Notably, BIK1 is a central signaling integrator that acts downstream of several PRRs and appears to be the merging node of a common PTI pathway. Yet, hardly anything is know about substrates for BIK1 and related PBL proteins, and thus on how these key regulators ultimately drive PTI signaling. The main objective of this joint project is to fill this gap by identifying and characterizing BIK1 (and PBLs) substrates capitalizing on the most recent findings and know-how from both laboratories in a collaborative and integrated approach.