Evolution from Free-Living Bacteria to Endosymbionts of Insects: Genomic Changes and the Importance of the Chaperonin Gr
Major insect lineages have independently acquired bacterial species, mainly from Gamma-proteobacteria and Bacteroidetes class, which could be nutritional mutualistic factories, facultative mutualists that protect against biotic and abiotic stresses, or re
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Evolution from Free-Living Bacteria to Endosymbionts of Insects: Genomic Changes and the Importance of the Chaperonin GroEL Beatriz Sabater-Muñoz and Christina Toft
Abstract Major insect lineages have independently acquired bacterial species, mainly from Gamma-proteobacteria and Bacteroidetes class, which could be nutritional mutualistic factories, facultative mutualists that protect against biotic and abiotic stresses, or reproductive manipulators (which alter the fertility of the host species in its benefit). Some of them are enclosed in bacteriocytes to assure their maternal transmission over generations. All of them show an increased level of genetic drift due to the small population size and the continuous population bottlenecking at each generation, processes that have shaped their genome, proteome, and morphology. Depending on the nature of the relationship, the degree of genome plasticity varies, i.e., obligate nutritional mutualistic symbionts have extremely small genomes lacking mobile elements, bacteriophages, or recombination machinery. Under these conditions, endosymbionts face high mutational pressures that may drive to extinction or symbiont replacement. How do then they survive for such long evolutionary time, and why do they show a genome stasis? In this chapter, after a brief introduction to the problem, we will focus on the genome changes suffered by these endosymbionts, and on the mutational robustness mechanisms, including the moonlighting chaperone GroEL that could explain their long prevalence from an evolutionary perspective by comparing them with free-living bacteria.
B. Sabater-Muñoz (*) Institute for Molecular and Cellular Biology of Plants (IBMCP), Spanish National Research Council (CSIC)–Polytechnic University of Valencia (UPV), Valencia, Spain Smurfit Institute of Genetics, Trinity College of Dublin (TCD), Dublin, Ireland e-mail: [email protected]; [email protected] C. Toft Smurfit Institute of Genetics, Trinity College of Dublin (TCD), Dublin, Ireland Institute for Integrative and Systems Biology (I2SysBio), Spanish National Research Council (CSIC)–University of Valencia (UV), Paterna, Spain e-mail: [email protected]; [email protected] © Springer Nature Switzerland AG 2020 M. Kloc (ed.), Symbiosis: Cellular, Molecular, Medical and Evolutionary Aspects, Results and Problems in Cell Differentiation 69, https://doi.org/10.1007/978-3-030-51849-3_3
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B. Sabater-Muñoz and C. Toft
Introduction: A Brief History about Symbiosis and its Importance in Insects’ Biology and Control
Symbiosis—from the Greek συμβίωσις (συμ ¼ sym, within; βίωσις ¼ biosis, living)—refers to any type of close and long-term interaction between two different organisms. The use of the term “symbiosis” became a controversy to describe the phenomenon of “living together” as reviewed in (Martin and Schwab 2012, 2013; Gontier 2016; Oborník 2019). Despite this controversy, symbiosis has been redefined in terms of the relationship between and physical location of partners. Depending on the type of relationships, s
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