Evolution of symbiotic bacteria within the extra- and intra-cellular plant compartments: experimental evidence and mathematical simulation (Mini-review)

Autor: Nicholas J. Brewin, Nikolay A. Provorov, Anna V. Tsyganova, Nikolay I Vorobyov, Viktor E. Tsyganov
Rok vydání: 2012
Předmět:
Zdroj: Symbiosis. 58:39-50
ISSN: 1878-7665
0334-5114
DOI: 10.1007/s13199-012-0220-0
Popis: Using the example of nodular legume-rhizobia symbiosis (LRS), we discuss the evolution in plant micro-symbionts of mutualistic traits that are apparently host-beneficial and therefore the products of inter-species evolution. These traits include: in planta activation of N2 fixation machinery; exporting the products of nitrogenase reaction into the plant cells/tissues; and the terminal differentiation of bacteria into non-reproductive N2-fixing bacteroids. It seems probable that such adaptive traits evolved by natural selection within the populations of endosymbiotic bacteria that colonize the extra- and intra-cellular compartments provided by the hosts (i.e., infection threads and symbiosomes). This evolution would occur under the impacts of group (inter-deme, kin) selection pressures induced by the partners’ metabolic and regulatory feedbacks that ensure the high activity of symbiotic N2 fixation. These important feedbacks include: progressive allocation of C compounds into N2-fixing nodules; maintenance of micro-aerobic intracellular environments that are indispensable for intensive N2 fixation; and stringent control by the host over bacterial reproduction in planta. A computational simulation of the associated co-evolutionary processes reveals the trade-off between inter-species and individual species components of progressive and adaptive LRS evolution. This is expressed as a correlated increase of ecological efficiency, functional integrity and genotypic specificity of mutualistic symbiosis. Thus, the evolution of rhizobia in symbiosis may be represented by a progressive multi-level scenario based on increasing the dependency of bacteria on the host-provided nutrients accompanied by increasing complexity of the bacterial genomes and of the symbiosis-encoding gene networks.
Databáze: OpenAIRE
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