Raphael Trösch - The regulation of chloroplast protein homeostasis: from chloroplast protein import to protein synthesis

The proteome of chloroplasts is constructed from proteins which are encoded on the nuclear genome and imported post-translationally via the translocons at the outer and inner chloroplast envelope membrane (TOC and TIC), as well as from proteins which are encoded on the chloroplast genome and translated on stromal ribosomes. The chloroplast proteome is thus modified by import, synthesis and degradation both during development and environmental stresses. While the protein import and translation machineries are well characterized, the recent focus of research has shifted towards the regulation of these processes. Forward genetics on protein import mutants led to the discovery of TOC regulation via the ubiquitin proteasome system. Furthermore, regulation of chloroplast translation as uncovered by ribosome profiling could be shown to be both specific and reversible during heat acclimation. While the steady state translational output of chloroplasts is remarkably conserved even between green alga and land plants, the common themes of regulation and acclimation need yet to be identified.