Regulation of plant receptor kinases in pattern triggered immunity

Project team leader: Dr. D. Chinchilla
Project team members: Dr. A. Dominguez, M. Kiss-Papp

In plants, as well as in animals, the understanding of the molecular mechanisms underlying the immune recognition and signaling system represents one of the most exciting challenges in the field of host-microbe interactions.

Immunity relies on the recognition of surrounding microbes and the induction of robust defense responses to prevent pathogen ingress. In contrast to animals which also have adaptive immunity mechanisms, plants rely solely on an innate immune system. Yet the plant immune system is efficient since, in nature, plants are generally resistant to most pathogens. The recognition of "non-self" occurs in part at the cell surface and is controlled by immune receptors, called pattern recognition receptors (PRRs). These receptors recognize molecules that are characteristic of a given group of microbes and referred to as microbe/pathogen associated molecular patterns (MAMPs or PAMPs). So far, a series of MAMPs originating from fungi, oomycetes and bacteria have been described that act as potent elicitors of defense responses in plants but many MAMPs and their specific PRRs remain to be identified in order to understand the plant immune system.

Our lab is interested in the molecular mechanisms of PRR activation and we use the plant paradigm for a PRR, the well-characterized FLS2 receptor kinase which recognizes flagellin, the main component of bacterial flagellum. Since 2003, we have been interested in understanding 1) how FLS2, a large and complex protein present in the plasma membrane, can recognize its ligand in the apoplast 2) how the signal is transferred across the plasma membrane to activate intracellular signaling.

Importantly we discovered that another receptor like-kinase called BAK1 (for BRI1-Associated Kinase1) acts as a positive regulator and partner for many PRRs, including FLS2. This is fascinating because this receptor like kinase is also involved in activation of the phytohormone receptor BRI1, another receptor kinase involved in plant development. With our recent work we showed that immediately after flg22 binding (<15 seconds) FLS2 and BAK1 associate in a stable complex and are phosphorylated in vivo. Thus these (trans) phosphorylation events are very likely responsible for the activation of intracellular signaling.

Overall our work aims at understanding the regulation of PRRs by BAK1 at the biochemical level, the repertoire of BAK1-regulated PRRs and more generally the role of BAK1 in plant immunity.

The seminal finding that BAK1 is involved in plant immunity paved the path for numerous recent publications in the plant research field.