OPR Protein-mediated Control and Adaption of Chloroplast Gene Expression in Chlamydomonas

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Due to the endosymbiotic origin of chloroplasts, many of the proteins constituting the multisubunit complexes of the thylakoid membrane are nowadays encoded in the nucleus while others are encoded in the chloroplast itself. Chloroplast gene expression therefore needs to be coordinated with the nuclear one to allow a balanced assembly of protein complexes. In addition, gene expression of the organelle requires an adaption to a changing environment, in particular light, to meet the demand of the cell. To date, the predominant role of Octotricopeptide Repeat proteins (OPRs) as key players for the posttranscriptional control of chloroplast gene expression in green algae is just emerging. The RNA targets of the majority of OPRs encoded by the algal genome as well as their molecular working modes are unknown. Moreover, the specific interaction of OPRs with their plastid target RNAs makes them ideal candidates as regulators of chloroplast gene expression for an adaption to changing light conditions. As photosystem II (PSII) is most susceptible to photodamage, the focus of the proposed project lies on OPRs with confirmed or expected functions in the expression of PSII subunits in the model organism Chlamydomonas reinhardtii. To gain further important insights into the OPR-mediated control and regulation of chloroplast gene expression, we aim at (I) elucidating the precise molecular working mode of two OPRs involved in the stabilization of two mRNAs encoding PSII subunits, (II) identify new OPRs involved in PSII biogenesis and (III) investigate the impact of these OPRs on light-dependent adaptive processes of the organelle.