The Roles of sRNAs in Regulating Stress Responses in Cyanobacteria

Abstract

Small RNAs (sRNAs) are transcriptional and posttranscriptional regulators of gene expression that play important roles in virtually every aspect of the life cycle of an organism, such as metabolic reactions, plasmid control, pathogenesis, and quorum sensing. Emerging evidence indicates that sRNAs also function in various stress responses. The large number of sRNAs present in organisms reflects the diverse roles of these molecules in adaptation to various environmental conditions. During the long period of evolution, sRNA regulatory networks have provided an economical and efficient way for organisms to adapt to various environmental stresses, as the regulation of gene expression by sRNAs likely requires fewer resources than protein-based gene regulation. Cyanobacteria, one of the most ancient life forms, include all types of photoautotrophic bacteria; these organisms are present in almost all environments on Earth. Recent investigations ofsRNA-mediated gene regulation in cyanobacteria have uncovered numerous novel mechanisms that display far more mechanistic complexity and regulatory features than those identified in other model microorganisms, such as Escherichia coli and yeast. These complex RNA-based regulatory mechanisms are thought to help cyanobacteria adapt to changes in their diverse environments. In this chapter, we critically review recent efforts to identify the roles of cyanobacterial sRNAs in stress responses and their potential implications for biological evolution. This chapter focuses on the biogenesis, conservation, functions, and traits of sRNAs, setting the course for future research on sRNAs in photosynthetic cyanobacteria.