Conservation and diversity in transcriptional responses among host plants forming distinct arbuscular mycorrhizal morphotypes

Summary The morphotype of arbuscular mycorrhizal (AM) roots is distinct mostly depending on AM host species: Arum , Paris , and Intermediate types. We previously reported that gibberellin (GA) promotes the establishment of Paris -type AM symbiosis in Eustoma grandiflorum despite its negative effects on Arum -type AM symbiosis in model plants. However, the molecular mechanisms underlying the differential effects of GA on different morphotypes, including Intermediate-type AM symbiosis, remain elusive. Comparative transcriptomics revealed that several symbiosis-related genes were transcriptionally promoted upon AM fungal colonization in Lotus japonicus ( Arum -type), Daucus carota (Intermediate-type), and E. grandiflorum ( Paris -type). Interestingly, upon GA treatment, the fungal colonization levels and expression of symbiosis-related genes were suppressed in L. japonicus and D. carota but were promoted in E. grandiflorum . Exogenous GA transcriptionally inhibited the biosynthetic process of a host-derived signal molecule involved in AM symbiosis, strigolactone, in L. japonicus and E. grandiflorum . Additionally, disaccharides mainly metabolized in AM roots would be different between L. japonicus and D. carota / E. grandiflorum . This study uncovered the conserved transcriptional responses during mycorrhization and diverse responses to GA in AM roots with distinct morphotypes among phylogenetically distant host plants.