P-414 - Immune modulation by the host's peptidyl-prolyl cis/trans isomerase in root nodule symbiosis

In symbiosis, hosts accept partners within their tolerance range by suppressing rejection. Legume-rhizobia symbiosis, widely known as root nodule symbiosis, embodies this principle. Legumes utilize an intracellular infection system involving tunnel-like structures to recruit compatible rhizobia. In this process, the hosts must properly control the immune response that could otherwise reject the symbionts. To explore how legumes engage with symbionts through post-translational regulation of immune responses, we focused on the peptidyl-prolyl cis/trans isomerase Cyclophilin A (CyPA). Previous studies have shown that Arabidopsis CyPA, especially its gain-of-function variant, suppresses immune responses against pathogens, an effect that may seem counterproductive for the host. Here, we hypothesized that native CyPA might fulfill a beneficial function in symbiotic interactions, such as facilitating the suppression of immune responses against compatible rhizobia. We analyzed CyPAs in the context of root nodule symbiosis using the model legume Lotus japonicus and found that one of CyPAs (named CyPA1) is required for intracellular infection in legumes. CyPA1 was associated with the immune hub RIN4, whose cis and trans conformations respectively promoted and inhibited symbiont acceptance. These results illuminate our understanding of mechanisms for acceptance of symbiotic partners.