**1. Introduction**

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Symbioses with beneficial microorganisms constitute the universal and ecologically highly effective strategy of adaptation of plants towards nearly all types of environmental challenges. Representatives of many groups of fungi and bacteria participate in plant-microbial symbioses (PMS) wherein they can colonize the plant surfaces, tissues or intra-cellular compartments using two basic adaptive strategies: nutritional and defensive. Construction of niches for hosting the symbiotic microbes involves the complicated developmental programs imple‐ mented under the joint control by plant and microbial partners and based on the crossregulation of their genes.

Legume plants (family Fabaceae) are known to form symbioses with extremely broad range of beneficial soil microorganisms (BSM), representing examples of almost all plantmicrobe mutualistic systems. Different groups of beneficial microbes improve host miner‐ al nutrition, acquisition of water, promote the plant development and offer protection from pathogens and pests. For ecology and agriculture, the most important beneficial le‐ gume symbioses are arbuscular mycorrhiza (AM) and root nodule (RN) symbiosis. These symbioses demonstrate high level of genetic and metabolic integrity, compared with oth‐ er interactions of legumes with plant growth-promoting rhizosphere bacteria (PGPR) and/or beneficial endophytic bacteria.

High integrity of AM and RN symbioses implies highly specific mutual recognition of partners, formation of special complex symbiotic compartments and integration of partners' metabolic pathways. In the symbioses, legume plant plays a role of the organizing center of the system as it performs functions of coordination and regulation of all developmental processes. During

© 2013 Zhukov et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Zhukov et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

last decade, a significant progress has been achieved in revealing the genetic bases of symbioses formation and functioning, so the knowledge of the plant genetic control over symbioses can effectively facilitate breeding new varieties of legumes that are needed for modern sustainable agriculture. In this chapter, we describe the present state of the developmental genetics of legume symbioses and depict the potential to organize the multi-component symbioses to be used for optimizing the broad spectrum of plant adaptive functions and to improve the sustainability of legume crop production.
