Evolution of TOR and translation control

The evolutionarily conserved serine/threonine protein kinase target of rapamycin (TOR) is a master controller of cell growth. TOR controls growth by promoting anabolic processes and inhibiting catabolic processes in response to nutrient availability, growth factors and cellular energy, which can be perturbed by environmental and cellular stresses. These upstream signals are integrated by TOR, which in turn modulates protein synthesis—an energetically demanding cellular process that requires tight regulation to minimize energy expenditure. The TOR pathway plays a central role in the control of protein synthesis through the phosphorylation of numerous substrates with well-characterized functions in ribosome biogenesis and the initiation and elongation steps of protein synthesis. The role of TOR in protein synthesis has been studied in extensive detail in several eukaryotic model systems, and consequently, a great deal is now known about how TOR controls protein synthesis in eukaryotes. In this book chapter, we provide an evolutionary perspective of the TOR pathway in the control of protein synthesis and ribosome biogenesis across eukaryotes (from unicellular to multicellular organisms).