Engineering of symbiotic bacteria for the sustainable crop production: search for the evolutionary based opportunities

摘要

Using the example of N_2-fixing legume-rhizobia symbiosis, we demonstrate that origin and evolution of beneficial micro-symbionts of plants involves: (1) emergence of novel sym gene networks based on the gene duplication-divergence and on the horizontal gene transfer between the diverse plant-associated microbes; (2) loss of genes encoding for free-living adaptations that are interfering with the. effective symbiosis development. Proceeding from the evolutionary knowledge, two approaches for genetic engineering of highly effective rhizobia strains are suggested: (1) amplification of positive symbiotic regulators (e.g. of dct genes responsible for dicarboxylate uptake by N_2-fixing bacteroids); (2) inactivation of negative symbiotic regulators (some genes responsible for sugar uptake, polysaccharide production or respiration). Both approaches should be combined with construction of the host plant genotypes capable for a complete assimilation of additionally fixed N and for its active allocation into shoots improving the crop productivity.