Control of defense hormone signaling by the symbiotic genes Does Not Fix nitrogen 2 and Does Not Fix nitrogen 5 in Medicago truncatula nodules

During symbiosis legumes develop specific organs, called nodules, where nitrogen fixing bacteria – the rhizobia – are hosted. Since the plant allows the presence inside cells of a large number of rhizobia without expressing defense-like reactions, this relationship is considered as a chronic infection of the nodules. The Medicago truncatula symbiotic genes Does not fix nitrogen 2 (DNF2) and Does not fix nitrogen 5 (DNF5) are necessary to reduce defenses in the nodules. In plant the hormones Ethylene (ET), Salicylic acid (SA) and Jasmonic acid (JA) play a role in defense. We thus looked for possible correlations between the action of these two symbiotic genes and defense hormones. Our work suggests that DNF2 and DNF5 might act through the defense hormone signaling pathways during the chronic infection in the M. truncatula genotypes Jemalong A17 and R108. Moreover, these experiments suggest additive or antagonist effects between the three hormones and, in particular, that Ethylene and Salicylic acid signaling pathways seem to be strongly linked.