Nikolai Provorov, Olga Onishchuk, Oksana Kurchak and Nikolai Vorobyov
All-Russia Research Institute for Agricultural Microbiology, Podbelsky sh., 3, Pushkin, St.-
Petersburg, 196608, Russia
Symbioses between N2-fixing bacteria and plants are broadly used in sustainable agriculture as an alternative for expensive and ecologically hazardous nitrogen fertilizers. The genetic methods for improving these symbioses should represent an extension of their natural evolution in which the gains of novel “symbiotic” gene systems by bacteria was combined with the losses of genes for free-living adaptations (e.g., photosynthesis and plant-independent diazotrophic growth). At the late stages of this evolution, many bacteria acquired the ability for “altruistic” transformation into non-viable cellular forms (e.g., bacteroids in rhizobia) which develop very high nitrogenase activity due to loss of their own reproductive ability. Using the model of rhizobialegume symbioses we suggest the three-stage algorithm amplification to improve the N2-fixing symbioses including: (i) increase of nitrogenase activity via amplifications of genes for nitrogenase synthesis or energy supply; (ii) bacteriacontrolled modifications of plant habitus (based on manipulating the plant hormonal status by the bacterial own synthesis of phytohormones or by modulating their production in plant cells) balancing the additional nitrogen accumulation and shoot mass yield; (iii) inactivation of negative symbioses regulators (bacterial eff genes) increasing the efficiency of altruistic bacteria-plant interaction. Parallel genetic modifications of plants and bacteria should be used for creating the optimal combinations of partners’ genotypes required for switching the legume and non-legume crops for symbiotrophic N nutrition and providing the ecologically safe production of plant biomass for food, fodder and pharmacological industries.