Role of RNA processing in the regulation of photosynthesis gene expression in Rhodobacter sphaeroides

• Applicant: Professorin Dr. Gabriele Klug
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms
• Term: from 2013 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 237518331

The process of photosynthesis enables living organisms to use sunlight as energy source. However the formation of photosynthetic complexes is an energy demanding process and in the presence of oxygen photosynthetic pigments contribute to the generation of reactive oxygen species. Rhodobacter sphaeroides is a facultative photosynthetic bacterium, which represses formation of photosynthetic complexes in the presence of high levels of oxygen or at intermediate oxygen tension when light is present. From intensive studies by my group and others a regulatory network for controlling photosynthesis genes in Rhodobacter emerged comprising a number of proteins, some of them redox- or light-responsive, or both. We have also shown in the past that differential stabilities of segments of polycistronic transcripts contribute to the stoichiometry of the different photosynthetic complexes. Over the last years many global approaches to analyze bacterial gene expression have been applied and small non-coding RNAs (sRNAs) and RNA-based regulatory processes were recognized as an additional important level of regulation. Our finding that the RNA chaperon Hfq influences formation of photosynthetic complexes supports an important role of RNA-based regulation in this process. We have recently identified and analyzed the sRNA PcrZ, which affects expression of photosynthesis genes by base pairing to mRNAs for pigment binding proteins or for enzymes of pigment synthesis. PcrZ is processed to smaller non-functional products and the processing pattern varies under different growth conditions. RNAseq has identified sRNAs within the photosynthetic gene cluster. RSspufX is localized downstream of the puf genes which encode reaction center and light harvesting I proteins. As well RSspufX as pufX mRNA were coimmunoprecipitated with Hfq. An antisense RNA RSaspufL overlaps the 5´end of the pufL coding region and we hypothesize that it influences the decay of the pufL mRNA segment. Both sRNAs influence the amount of photosynthetic complexes when overexpressed in R. sphaeroides. The regulatory functions of RSspufX and RSaspufL should be elucidated. The main focus of this proposal is on the mechanisms that determine the stability of the sRNAs affecting photosynthesis gene expression and their targets. The goal is to find out, how growth conditions influence the processing steps and consequently gene expression. Growth conditions may alter the accessibility of the RNA or the amount or activity of RNases. The results of this study will also increase our general understanding of the mechanisms of RNA processing and degradation and their role in gene regulation in alpha-proteobacteria.

• DFG Programme: Research Grants