Characterization of novel mutants in the Chloroplast Unfolded Protein Response of Chlamydomonas reinhardtii

Green algae and land plants play a pivotal role in supporting life on Earth through photosynthesis. The process of photosynthesis takes place inside their chloroplasts, intracellular organelles that are enclosed by a double membrane and contain a semi-autonomous gene expression system. These organisms have, therefore, developed a plethora of mechanisms to ensure that their chloroplasts function efficiently under a wide range of environmental conditions. One mechanism through which protein homeostasis is maintained is the chloroplast unfolded protein response (cpUPR). The cpUPR is activated in response to chloroplast proteotoxic stress and triggers the transcriptional up-regulation of hundreds of nuclear genes encoding factors that can alleviate chloroplast protein damage and its cellular consequences. As of today, only one cpUPR player has been discovered and characterized, "Mutant Affecting chloroplast-to-nucleus Retrograde Signaling 1" (MARS1), a cytosolic kinase. Therefore, it is reasonable to speculate the existence of upstream components that relay signals from the chloroplast as well as downstream components that transduce the signal to the nucleus. In my thesis project I aim to identify additional key cpUPR players in the green alga Chlamydomonas reinhardtii as a model system. Conducive to this goal, I adopt a forward genetic screen and a suppressor screen followed by the characterization of the most promising candidates with various drug treatments, qRT-PCR and immunoblot analysis. Ultimately, advancing our mechanistic understanding of cpUPR will contribute to a better understanding of how plants cope and adapt to environmental stressors that cause chloroplast protein damage.