FSBSI ARRIAM
Federal State Budget Scientific Institution
All-Russia Research Institute for Agricultural Microbiology
All-Russia Research Institute for Agricultural Microbiology
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The symbiosis of pea with nodule bacteria is an example of a highly specific interaction. Peas, like other legumes, secrete flavonoid molecules in their root exudates, which attract a certain type of rhizobia – Rhizobium leguminosarum – and activate the expression of symbiotic genes in bacterial cells. In turn, rhizobia secrete signal molecules – Nod factors – which are recognized by plant receptors. If the bacteria are successfully recognized as suitable symbionts, the plant initiates a program for the development of new organs – nitrogen-fixing nodules – and allows the bacteria to penetrate into them.
The structure of Nod factors secreted by a specific rhizobia strain is determined by the set of its symbiotic genes. Pea varieties originating from Afghanistan form nodules only with Rhizobium leguminosarum strains that have the nodX gene in their genome, encoding acetyltransferase that modifies the structure of the Nod factor. In turn, modern European pea varieties interact with Rhizobium leguminosarum strains regardless of the presence of the nodX gene in their genomes. The manifestation of the specificity trait from the plant’s side is controlled by the Sym2 gene, the most likely candidate for which is the LykX gene, which we identified several years ago (Sulima et al., 2017). The LykX gene encodes a receptor kinase likely involved in recognizing the structure of Nod factors. The LykX allelic state is unique to pea accessions from Afghanistan and differs from the LykX sequence in European cultivars. Recently, a new allelic variant of LykX was identified in pea accessions from Tajikistan, differing from the European alleles by a single substitution that likely affects the manifestation of the symbiosis specificity trait (Sulima et al., 2019).
Modern pea varieties are capable of interacting with a wide range of strains of nodule bacteria living in the soils of the Russian Federation, but these strains are characterized by low efficiency of nitrogen fixation. Selected strains used in new-generation biopreparations, on the contrary, effectively fix nitrogen, but lose the competition with native strains when introduced into the soil. This problem can be solved by creating pea varieties with artificially narrowed specificity of interaction with nodule bacteria, which will protect plants from native microflora and ensure the formation of nodules with highly effective strains introduced as part of biopreparations.
To achieve this goal, within the framework of a joint project with Sirius University of Science and Technology, genetic editing of the pea gene LykX, encoding a receptor for signaling molecules that determines the specificity of interaction with nodule bacteria, is being carried out. In a field experiment, it was shown that introgression of "wild" alleles of the LykX gene into the genome of the pea cv. Rondo ensures penetration of the TOM strain (carrying the nodX gene), used for inoculation, into 95% of the nodules, while in the original cv. Rondo, the TOM strain was found in only 7% of the nodules (Sulima et al., 2025). In the course of the current work, the method of genomic editing of peas is being optimized to create a technology that allows for a targeted narrowing of the specificity of interaction of modern pea varieties, thereby guaranteeing the formation of a highly effective microbial-plant system in field conditions.
Interestingly, a certain allelic state of the specified LykX gene is associated with increased seed productivity when growing plants in symbiotic conditions (Sulima et al., 2017; Zhukov et al., 2021b). This result also highlights the importance of manipulating the microbial-plant signaling interactions to achieve high crop yields.
