Molecular mechanisms regulating cell death function and membrane localization of potentially N-terminal acylated plant CNL-type immune receptors.

• Applicant: Dr. Farid El Kasmi
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems ; Plant Genetics and Genomics ; Plant Physiology ; Plant Breeding and Plant Pathology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 490734579

Plant intracellular immune receptors of the nucleotide-binding leucine-rich repeat receptor (NLR) family recognize pathogen-derived effectors to initiate effector-triggered immunity (ETI). The current hypothesis for NLR, specifically CNL (coiled-coil (CC)-domain containing NLRs) and helper NLR function is that activation leads to the formation of an oligomeric complex at the plasma membrane, where the very N-terminal alpha-helix of the CC domains might form a membrane penetrating pore required for cell death initiation upon NLR activation in ETI. We have recently contributed to an important study supporting the model of pore formation and localization at membranes of CNLs and helper NLRs. Membrane localization is important for the function of many CNLs and membrane localization is often mediated by the CC domain. However, we are only beginning to understand the exact mechanism of how CNL proteins initiate cell death during ETI or auto-immunity. We have identified phylogenetically related CNLs, characterized by a potential N-terminal myristoylation and palmitoylation (PM) site. In Arabidopsis this subclade of ‘PM CNLs’ includes well characterized CNLs like RPS5, SUMM2, SUT1 or UNI. Interestingly, one PM CNL, At1g61300/PM5, has a variant CC domain with a 115 amino acid deletion. We have started to characterize this ‘truncated’ PM NLR in more detail and can show that, in spite of the deletion, PM5 has canonical cell death activity. Furthermore, expression of the first 60 amino acids of PM5 are sufficient for cell death initiation. Full-length PM5 localizes to Golgi membranes and the tonoplast, and PM5 expression induces a vacuolar vesiculation and nuclear expansion phenotype. Interestingly, pm5 mutants, as well as mutants of other members of this PM CNL clade, are more susceptible to infections with the virulent bacteria Pseudomonas syringae, indicating an important function for plant immunity. We have established a unique experimental framework for the analysis of CNL-mediated cell death by exploiting diverse approaches to uncover mechanisms of regulation and activity of this truncated CNL PM5 - a unique CNL, potentially stripped off by evolution to the minimal required features for CNL function. PM5 is an extraordinary example to obtain new and important insights into the minimal requirements for CNL cell death activity, immune functions and regulation. We will investigate how pm5 mutants affect plant immunity, and define what immune sectors/regulators are required for PM5-induced phenotypes. Further, are we aiming to identify components regulating PM5 function and required for downstream responses initiated upon PM5 (auto-)immunity, and to elucidate the molecular mechanisms of PM5-mediated cell death and PM5-triggered vacuolar vesiculation.

• DFG Programme: Research Grants