Matching population diversity of rhizobial A and legume genes in plant-microbe symbiosis.

We hypothesized that population diversities of partners in nitrogen-fixing rhizobium-legume symbiosis can be matched for "interplaying" genes. We tested this hypothesis using data on nucleotide polymorphism of symbiotic genes encoding two components of the plant-bacteria signaling system: (a) the rhizobial A acyltransferase involved in the fatty acid tail decoration of the Nod factor (signaling molecule); (b) the plant receptor required for Nod factor binding. We collected three wild-growing legume species together with soil samples adjacent to the roots from one large 25-year fallow: , , and nodulated by one of the two biovars ( and ).

Investigation of the core microbiome in main soil types from the East European plain.

The main goal of modern microbial ecology is to determine the key factors influencing the global diversity of microorganisms. Because of their complexity, soil communities are largely underexplored in this context. We studied soil genesis (combination of various soil-forming processes, specific to a particular soil type) that is driven by microbial activity.

The preservation of microbial DNA in archived soils of various genetic types.

This study is a comparative analysis of samples of archived (stored for over 70-90 years) and modern soils of two different genetic types-chernozem and sod-podzolic soils. We revealed a reduction in biodiversity of archived soils relative to their modern state. Particularly, long-term storage in the museum exerted a greater impact on the microbiomes of sod-podzolic soils, while chernozem samples better preserved the native community.

Simulation of evolution implemented in the mutualistic symbioses towards enhancing their ecological efficiency, functional integrity and genotypic specificity.

We created the mathematical model for the evolution of the Efficiency of Mutualistic Symbioses (EMS) which was estimated as the microsymbiont impacts on the host's reproductive potential. Using the example of rhizobia-legume interaction, the relationships were studied between EMS and Functional Integrity of Symbiosis (FIS) which is represented as a measure for concordance of changes in the partners' genotypic frequencies under the environmental fluctuations represented by the minor deviations of the systemic model parameters. The FIS indices correlate positively with EMS values suggesting an enhancement of FIS via the natural selection operating in the partners' populations in favor of high EMS.

Equilibrium between the "genuine mutualists" and "symbiotic cheaters" in the bacterial population co-evolving with plants in a facultative symbiosis.

The mathematical model for evolution of the plant-microbe facultative mutualistic interactions based on the partners' symbiotic feedbacks is constructed. Using the example of rhizobia-legume symbiosis, we addressed these feedbacks in terms of the metabolic (C<-->N) exchange resulting in the parallel improvements of the partners' fitness (positive feedbacks). These improvements are correlated to the symbiotic efficiency dependent on the ratio of N(2)-fixing bacterial strains ("genuine mutualists") to the non- N(2)-fixing strains ("symbiotic cheaters") in the root nodules.

Cooperation of plants and microorganisms: getting closer to the genetic construction of sustainable agro-systems.

The molecular research into two types of beneficial plant-microbe symbioses is reviewed: nutritional (with N(2)-fixing bacteria or mycorrhizal fungi) and defensive (with endo- and epiphytic microbes suppressing pathogens and phytophagans). These symbioses are based on the signaling interactions that result in the development of novel tissue/cellular structures and of extended metabolic capacities in the partners, which greatly improve the adaptive potential of plants due to a decrease in their sensitivity to biotic and abiotic stresses. The molecular, genetic and ecological knowledge on plant-microbe interactions provides a strategy for the organization of sustainable crop production based on substituting the agrochemicals (mineral fertilizers, pesticides) by microbial inoculants.

Interplay of Darwinian and frequency-dependent selection in the host-associated microbial populations.

In order to analyze the microevolutionary processes in host-associated microorganisms, we simulated the dynamics of rhizobia populations composed of a parental strain and its mutants possessing the altered fitness within "plant-soil" system. The population dynamics was presented as a series of cycles (each one involves "soil-->rhizosphere-->nodules-->soil" succession) described using recurrent equations. For representing the selection and mutation pressures, we used a universal approach based on calculating the shifts in the genetic ratios of competing bacterial genotypes within the particular habitats and across several habitats.

Developmental genetics and evolution of symbiotic structures in nitrogen-fixing nodules and arbuscular mycorrhiza.

Genetic and molecular mechanisms of development are compared for two major plant-microbe endosymbioses: N(2)-fixing nodules (with rhizobia or actinomycetes Frankia) and arbuscular mycorrhiza (with Glomales fungi). Development from the primordia formed de novo in root tissues is common for all known types of N(2)-fixing nodules. However, their structure varies greatly with respect to: (i) tissue topology (location of vascular bundles is peripherical in legumes or central in non-legumes); (ii) position of nodule primordium (inner or outer cortex in legumes, pericycle in non-legumes); (iii) stability of apical meristem (persistent in the indeterminate nodules, transient in the determinate ones).