Hsp-associated proteasomal plastid pre-protein degradation as a regulatory and quality control mechanism in plants

Protein homeostasis is a delicate process which keeps the synthesis, folding, trafficking and degradation of proteins in balance. Itsdisruption is linked to various diseases, including neurodegenerative disorders, cancer, and ageing in metazoan species. In plants,protein homeostasis is critical for survival under environmental stresses like extreme temperatures, drought, and pathogen infections.As the global population nears 8 billion, ensuring an adequate food supply is paramount, especially while coping with the adverseeffects of climate change. Chloroplasts (plastids), crucial organelles in plant cells, are responsible for producing most of the world'sfood, and require the import of over 3000 different proteins for their proper function.My research objective is to investigate the evolutionarily conserved CHIP-Bag1-Hsp70 system (CHIP), a vital quality controlmechanism for chloroplast protein import and clearing of unimported and misfolded precursor proteins. CHIP is part of the largerUbiquitin-Proteasome System (UPS). Despite its significance, CHIP's interactions and substrates in plants are poorly understood. Thegoal of my research is to (1) identify CHIP interactors and substrates in plants, using techniques like affinity purification, proximitylabeling, and proteomics; (2) study the structural organization of these complexes and their interactions with substrates throughstructural mass spectrometry; and (3) determine how these complexes interact with the proteasome using cryo-electron microscopy.This research sheds light on an inadequately understood system crucial for chloroplast regulation and various biological processes. Italso lays the foundation for studying the UPS in important plant models. Ultimately, this work indirectly contributes to enhancingcrop resilience against diseases and heat stress, which is increasingly relevant in the context of global warming.