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

光合作用的过程使生物体能够利用阳光作为能量来源。然而，光合复合体的形成是一个需要能量的过程，在氧气存在的情况下，光合色素有助于活性氧的产生。球形红杆菌是一种兼性光合细菌，它在高水平的氧气存在下或在有光的情况下在中等氧张力下抑制光合复合体的形成。通过我的小组和其他人的深入研究，一个控制红杆菌光合作用基因的调节网络出现了，它由许多蛋白质组成，其中一些是氧化还原或光反应的，或者两者兼而有之。我们也在过去表明，不同的多顺反子转录片段的稳定性有助于不同的光合复合体的化学计量。在过去的几年里，许多分析细菌基因表达的全球方法已经被应用，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。我们发现RNA伴侣子Hfq影响光合复合体的形成，这支持了RNA调控在这一过程中的重要作用。我们最近发现并分析了sRNA PcrZ，它通过与色素结合蛋白或色素合成酶的mrna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，不同的生长条件下加工模式不同。RNAseq已经鉴定出光合作用基因簇中的sRNAs。RSspufX位于puf基因的下游，而puf基因编码反应中心和光收获I蛋白。RSspufX和pufX mRNA均与Hfq共免疫沉淀。反义RNA RSaspufL重叠在pufL编码区的5′端，我们假设它影响了pufL mRNA片段的衰减。当这两种sRNAs在球孢中过表达时，都会影响光合复合体的数量。RSspufX和RSaspufL的调控功能有待阐明。本提案的主要重点是确定影响光合作用基因表达的sRNAs及其靶标的稳定性的机制。目的是找出生长条件是如何影响加工步骤和基因表达的。生长条件可能改变RNA的可及性或RNA酶的数量或活性。本研究的结果也将增加我们对α -变形菌中RNA加工和降解的机制及其在基因调控中的作用的一般理解。

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.