Strigolactones: promising plant signals.

As obligate biotrophic symbionts, Arbuscular Mycorrhizal (AM) fungi must efficiently recognize their host plant to insure their survival and complete their life cycle. Recent works have shown that some root secreted molecules, the strigolactones, activate the presymbiotic growth of AM fungi at extremely low concentrations. These compounds, derived from carotenoid biosynthesis, induce the mitochondrial metabolism of the fungus. The hypothesis that strigolactones are important plant recognition signals for AM fungi was further supported in this study by using maize seedlings treated with fluridone, an upstream inhibitor of the carotenoid metabolism. We showed that mycorrhization of the treated seedlings was significantly reduced, but restored by the addition of GR24, a strigolactone analogue. Similar results were obtained with the y9 mutant of maize defective in an upstream step of carotenoid synthesis. These data provide additional evidence that strigolactones may be essential symbiotic signals for the establishment of AM symbiosis.