Unfolded protein responses in Chlamydomonas reinhardtii.

The disruption of protein homeostasis leads to the increased un- and misfolding of proteins and the formation of toxic protein aggregates. Their accumulation triggers an unfolded protein response that is characterized by the transcriptional upregulation of molecular chaperones and proteases, and aims to restore proteome integrity, maintain cellular function, suppress the cause of perturbation, and prevent disease and death. In the green microalga Chlamydomonas reinhardtii, the study of this response to proteotoxic stress has provided insights into the function of chaperone and protease systems, which are, though simpler, closely related to those found in land plants. In addition, there has been considerable progress in understanding the triggers and regulation of compartment-specific unfolded protein responses. This review provides an overview on how the dysfunction of protein homeostasis is sensed in the different compartments of Chlamydomonas, and summarizes the current knowledge on the pathways that are triggered to restore equilibrium in the cell, while also highlighting similarities and differences to the unfolded protein responses of other model organisms.