Symbiosis in legume plant Pisum sativum upon Nod factor stimulation
It was suggested previously, that Nod factors may suppress defense activation during legume-rhizobial symbiosis, providing effective inoculation of plants by rhizobia, searching of possible mechanisms of such regulation is important. In the present study, we observed that Nod factors may effectively suppress the expression of genes encoding the defense markers (WRKYs, PRs, PALs), as well as ROS formation, and decrease the content of pattern recognition receptor (PRR) LYK9 induced by CO8-DA treatment in pea roots. Since PRR LYK9 may recognize not only chitin/COs, but peptidoglycan, it can play an important role in activation of the defense responses during rhizobial inoculation. This indicates the need to suppress the activity of PRR during symbiosis. To identify a number of potential regulators through which Nod factors can suppress the development of the immune response in plants during symbiosis with rhizobia, the analysis of proteome and transcriptome was performed in our experimental work. Indeed, comprehensive analysis allowed to identify a few potential candidates activated by Nod factors. We showed that synthesis of superoxide dismutase and catalase enzymes, which block excessive accumulation of ROS and prevent the development of oxidative stress, increases significantly in the pea root proteome in response to effective A34 strain in 24 h, but not to defective in Nod-factor production A56 strain (nodC-). Nod factors activate enzymes may be involved in the production of JA, it in turn can activate the transcription factor ABR1, turning off the ABA-induced responses and decreasing the immune response in plants. We also found the ubiquitin-ligases and ubiquitin-conjugating enzymes, because the PRRs activated as an initial response to rhizobial inoculation may be their potential targets. It was shown, that degradation of PRRs by means of activated by Nod factors ubiquitinylating may prevent an excessive immune response in legumes. We showed that LysM (Lysin motif)-receptor-like kinases (LysM-RLK) PsLYK11/MtLYK11, the probable homologs of Arabidopsis LysM-RLK AtLYK3 in pea and Medicago, are involved in regulation of the immune response.