IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

17 th International Congress on Nitrogen Fixation
Fremantle, Western Australia
27 November – 1 December 2011
Session Details: Monday 28 November 2011
Concurrent Session 3 – Taxonomy & Evolution
1530 - 1650
Authors: Nikolay Provorov & Nikolay Vorobyov
All-Russia Research Institute for Agricultural Microbiology, Podbelsky Sh., 3, Pushkin,
196608, St.-Petersburg, Russia
Presentation Title: Mathematical simulation of evolutionary events in the N2-fixing plant-microbe symbioses
Presentation Time: 1530 - 1550
A series of mathematical models is constructed for simulating the evolution of N2-fixing nodular symbioses
towards their improved ecological efficiency (Provorov & Vorobyov 2010a 2010b). By comparing the contrast
forms of legume-rhizobia symbioses formed by plants from different phylogenetic groups of the Fabaceae we for
the first time differentiate the modes and estimate the pressures of individual and group natural selection which
supports the transitions from: (i) mixed to clonal infections of hosts by rhizobia; (ii) extra-cellular maintenance of
rhizobia (inside infection/fixation threads) to their intra-cellular maintenance inside symbiosomes; (iii)
unspecialized (multi-bacterial) symbiosomes to the specialized (mono-bacterial) symbiosomes in which the
rhizobia are transformed into non-reproducible bacteroids. We also quantified the impacts of genotypic specificity
of partners‟ beneficial interaction on the symbiosis evolution: the host-specific microsymbionts obtain a more
pronounced selective support and remain stably mutualistic during a prolonged macroevolutionary process while
the non-host-specific microsymbionts may be transformed readily into the hosts‟ antagonists. Therefore, nodular
symbioses provide us the unique models to study the population-genetic background for progressive evolution
which is poorly investigated in the free-living unitary organisms. The developed simulation techniques may be
used for assessing the evolutionary processes in agriculturally important symbioses induced by: (i) introductions
of cultivated legumes into the novel cropping areas; (ii) release of the genetically modified rhizobia strains into
sustainable agricultural systems. Supported by RFBR grant 09-04-00907a.
Provorov NA & Vorobyov NI (2010a). Evolutionary Genetics of Plant-Microbe Symbioses. Ed I Tikhonovich
NOVA Sci Publ NY 290 p.
Provorov NA & Vorobyov NI (2010b). Simulation of evolution implemented in the mutualistic symbioses towards
enhancing their ecological efficiency, functional integrity and genotypic specificity. Theor Popul Biol 78: 259-269.
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2011