Arbuscular mycorrhizal fungi induce lateral root development in angiosperms via a conserved set of MAMP receptors

Root systems regulate their branching patterns in response to environmental stimuli. Lateral root develop-ment in both monocotyledons and dicotyledons is enhanced in response to inoculation with arbuscular mycorrhizal (AM) fungi, which has been interpreted as a developmental response to specific, symbiosis -acti-vating chitinaceous signals. Here, we report that generic instead of symbiosis-specific, chitin-derived mole-cules trigger lateral root formation. We demonstrate that this developmental response requires the well-known microbe-associated molecular pattern (MAMP) receptor, Chitin Elicitor Receptor Kinase 1 (CERK1), in rice, Medicago truncatula, and Lotus japonicus, as well as the non-host of AM fungi, Arabidopsis thaliana, lending further support for a broadly conserved signal transduction mechanism across angiosperms. Using rice mutants impaired in strigolactone biosynthesis and signaling, we show that strigolactone signaling is necessary to regulate this developmental response. Rice CERK1 operates together with either Chitin Elicitor Binding Protein (CEBiP) or Nod Factor Receptor 5 (NFR5) in immunity and symbiosis signaling, respectively; for the lateral root response, however, all three LysM receptors are required. Our work, therefore, reveals an overlooked but a conserved role of LysM receptors integrating MAMP perception with developmental re-sponses in plants, an ability that might influence the interaction between roots and the rhizosphere biota.

Automated summary

This study reveals that chitin-derived molecules, rather than symbiosis-specific signals, can trigger lateral root formation. The LysM receptors integrate MAMP perception with developmental responses, and their role in coordinating the interaction between roots and the rhizosphere biota is conserved across different plant species.