P-441 - The PTI or the ETI? Unveiling BAK1-INTERACTING RECEPTOR Evolution and Functional Diversity

BAK1-INTERACTING RECEPTOR-LIKE KINASE (BIR) proteins are negative regulators of BRI1-ASSOCIATED KINASE 1 (BAK1) complex formation with pattern recognition receptors (PRR) and negative regulators of cell death by suppression of a nucleotide binding-leucine-rich repeat (NLR) protein CONSTITUTIVE SHADE AVOIDANCE 1 (CSA1). BIR proteins can interact with both BAK1 and CSA1, thereby linking surface pattern-triggered immunity (PTI) receptors to intracellular effector-triggered immunity (ETI) receptors. CSA1 guards homeostasis of BAK1/BIR3 receptor complexes and is required to activate full immunity without affecting classical PTI responses. Within the BIR protein family of four members, the two traits -suppression of BAK1 complex formation and cell death control-are distributed antagonistically. To correlate the two traits within the BIR family, we used AlphaFold-predicted structures to uncover interaction interfaces with BAK1 and CSA1. We are currently working on the impact of the unveiled interfaces and correlating it to cell death control and PTI. We exploit the evolutionary sequence and structural adaptations correlated with immune outcomes to study how BIR proteins interfere with the two branches of plant immunity. In conclusion, our research offers insights into the evolutionary dynamics and functional diversification of BIR family proteins, providing a foundation for understanding the integration of PTI and ETI for full immunity.