Cells sense extracellular signals via their surface localized transmembrane receptor kinases. Although long regarded as a conduit for cell surface receptor degradation or recycling, the endosomal system is also an essential site for signal transduction. Say endosomes are the logistics platforms for receptors, activated receptors accumulate in endosomes, and certain signaling components are exclusively localized to endosomes. Receptors can continue to transmit signals from endosomes that are different from those that arise from the plasma membrane, resulting in distinct physiological responses. In mammals, endosomal signaling was demonstrated for many receptor families including receptor tyrosine kinases, G‐protein‐coupled receptors and toll‐like receptors. Unlike mammals, the mechanisms of endosomal signaling in plants are unknown. Recent study of the immune receptor PEPR1 that perceives the endogenous peptide Pep1, showed that endocytosis is required for mitogen-activated protein kinase (MAPK) activation after elicitation with Pep1. However, because MAPK activation occurs faster than the endocytosis of the main receptor it raised the question if endocytosis of so far unknown signaling components is required for Pep1-elicited immune responses. In ENDOLOGISTIC, I aim to identify those components. To reach this goal, I will perform proteomics and phosphoproteomics analyses on isolated endosomes after elicitation with Pep1. This will enabled me to map and to correlate endosomal-specific phosphorylation with changes in subcellular protein distribution. Furthermore, I will employ the proximity labelling method to identify components of both the PEPR1 signaling complex and endosomal or autophagy machinery. In ENDOLOGISTIC I will combine my expertise in immunity with state -of- the -art proteomics, live cell imaging and genome-editing techniques available at the host institute to further advance our understanding of how endocytosis controls immunity in plants.
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