Projects on PPR-Proteins

PPR proteins as regulators of the acclimation of chloroplast RNA metabolism (team H. Ruwe)

Pentatricopeptide repeat (PPR) proteins are RNA-binding proteins with high specificity. This protein family is present in almost every eukaryotic genome. Encoded in the nuclear genome, most members are imported post-translationally into the two endosymbiotic organelles, the mitochondrion and the chloroplast. In these DNA-containing organelles they bind RNA transcripts and influence organellar gene-expression post-transcriptionally.

Plants as sessile organisms need to acclimate to environmental conditions. In temperate regions plants experience low temperatures and shorter day-length during winter and elevated temperatures with increased light intensities during summer. Temperature and light quantities are integrated by plants and result in acclimation responses that include reprogramming of gene expression patterns.

The genes encoded in the chloroplast genome are regulated predominantly on the post-transcriptional level. PPR proteins impact RNA stability and influence the rate of translation of individual chloroplast mRNAs. Our goal is to understand how PPR proteins reprogram chloroplast gene-expression in response to environmental signals, especially temperature.

 

 

 

PPR proteins as biotech tools (team C. Schmitz-Linneweber)

The chloroplast is a prime target for genetic engineering in plants, offering various advantages over nuclear transformation. For example, chloroplasts allow the expression of polycistronic transcripts and thus to engineer complex metabolic pathways. Each cistron within such a longer transcript needs its own expression elements. Within the 5’-UTR, such expression elements are needed for stabilizing mRNAs and for translation of the downstream reading frame.

Key players in chloroplast transcript stabilization and translation are pentatricopeptide repeat (PPR) proteins. PPR proteins that stabilize mRNAs leave behind short RNA footprints that are indicators of their activity. We identified such sRNAs in various plant species and have used them to stabilize and stimulate translation of mRNAs from synthetic transgenes in chloroplasts. Our goal is to develop a PPR protein-based toolbox to allow expression of various transgenes. Currently, we are focusing on the production of antigens for vaccination and on the production of enzymes relevant for biotechnological applications.

 

Publications

Legen J, Ruf S, Kroop X, Wang G, Barkan A, Bock R, Schmitz-Linneweber C
Stabilization and translation of synthetic operon-derived mRNAs in chloroplasts by sequences representing PPR protein-binding sites. Plant J. 2018 Apr;94(1):8-21. doi: 10.1111/tpj.13863.