Chloroplastidäre Ribonukleoproteine (cpRNPs): globale Stabilisatoren chloroplastidärer RNA-Reservoirs während der Stressantwort

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Chloroplast RNA processing is mediated by a multitude of nuclear-encoded RNA binding proteins. Despite growing knowledge on the factors involved and mechanistic questions of individual gene expression steps being addressed, we still know little about the truly regulatory steps of chloroplast gene expression. Nor do we understand how chloroplast genes are co-regulated and how chloroplast gene expression is acclimated to changing external conditions. We have recently demonstrated that chloroplast ribonucleoproteins (cpRNPs) impact chloroplast mRNA accumulation and processing under low temperature conditions on a global scale. Unpublished experiments furthermore demonstrate that cpRNPs globally bind RNAs freed from chloroplast ribosomes under conditions of translational stress. cpRNPs are expressed and phosphorylated in a light and temperature-dependent manner. Taken together, cpRNPs have the unique potential to act as global modulators of external signals towards chloroplast RNA pools. We propose to address the following questions:I. How do RNA-pools bound by cpRNPs and by ribosomes, respectively, correspond to each other during stress acclimation?II. How does phosphorylation impact the role of cpRNPs and what are the kinases linking cpRNPs to external signals?III. How do cpRNPs mediate cold-resistance in Arabidopsis?IV. What is the molecular mechanism of cpRNP action, in particular, what are the exact binding sites on chloroplast mRNAs?We will use genome-wide quantitative profiling of RNA ligands of cpRNPs (RIP-Chip and iCLIP) to determine the role of cpRNPs and their known phosphorylation sites during acclimation processes. Furthermore, we will identify kinases acting upon cpRNPs using a combination of genetic and biochemical approaches. Finally, pharmacological, genetic and physiological perturbations of chloroplast gene expression will be harnessed to determine, at what time during development and stress acclimation cpRNPs are important to provide stability to chloroplast mRNAs. In sum, our analysis is designed to unravel, how chloroplast RNA metabolism is controlled and executed by cpRNPs on a global scale in response to stressors relevant for chloroplast function and plant survival.