Legume plants have acquired the ability to obtain nitrogen sources through symbiosis with nitrogen-fixing bacteria, rhizobia. In this symbiosis, excessive infection of rhizobia inhibits the growth of the host plants. Therefore, suppression system of a rhizobial infection to optimize the number of rhizobia is important. In this study, Akira Akamatsu and his colleagues revealed that the rhizobial infection suppression system is regulated by phosphatidylinositol (PI), a plasma membrane glycerolipid, and clarified its suppression mechanism.
　In this study, Dr. Akamatsu and his colleagues focused on PITP-like protein (PLP), which encodes a transport protein for PI whose expression is up-regulated during rhizobial infection. In the mutants of PLP rhizobial infection was increased and failed to induce accumulation of PI. Observation of PI using a fluorescent marker in rhizobia-infected roots found that the ectopic accumulation of PI is closely related to the suppression of rhizobial infection. Based on these findings, Dr. Akamatsu and his colleagues conclude that there is a rhizobial infection inhibitory pathway that acts by the accumulation of PI and they suppress rhizobial infection to maintain optimal infection levels.