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

光合作用的过程使生物能够利用阳光作为能源。然而，光合作用复合体的形成是一个耗能的过程，在氧气存在的情况下，光合色素有助于产生活性氧物种。球形红杆菌是一种兼性光合作用细菌，在高氧或中等氧分压下抑制光合作用复合体的形成。从我的团队和其他人的深入研究中，我们发现了一个控制红细菌光合作用基因的调控网络，它由许多蛋白质组成，其中一些蛋白质对氧化还原或光反应，或者两者兼而有之。我们在过去也表明，多顺反子转录本片段的不同稳定性有助于不同光合作用复合体的化学计量。在过去的几年里，许多全球性的方法被用来分析细菌的基因表达，小的非编码RNA(SRNAs)和基于RNA的调控过程被认为是另一个重要的调控水平。我们的研究发现，RNA伴侣Hfq影响光合作用复合体的形成，这支持了基于RNA的调控在这一过程中的重要作用。我们最近已经鉴定并分析了sRNA PcrZ，它通过与色素结合蛋白或色素合成酶的mRNAs碱基配对来影响光合作用基因的表达。PCrZ被加工成较小的非功能性产品，并且在不同的生长条件下加工模式不同。RNAseq已经在光合作用基因簇中发现了sRNA。RSspufX位于PUF基因下游，PUF基因编码反应中心和捕光I蛋白。RSspufX AS pufX mRNA与Hfq免疫共沉淀。反义RNA RSaspufL重叠在pufL编码区的5‘端，我们推测它影响pufL mRNA片段的衰退。这两个sRNA在球藻中过表达时都会影响光合作用复合体的数量。RSspufX和RSaspufL的调控功能有待阐明。这一建议的主要焦点是决定影响光合作用基因表达的sRNA及其靶标的稳定性的机制。我们的目标是找出生长条件如何影响加工步骤，从而影响基因表达。生长条件可能会改变RNA的可及性或核糖核酸酶的数量或活性。这项研究的结果也将增加我们对RNA加工和降解的机制以及它们在α-蛋白细菌基因调控中的作用的总体理解。

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.