A rhizobacterium-secreted protein induces lateral root development through the IAA34-PUCHI pathway

Highlights•Bacillolysin identified from B. velezensis SQR9 can promote lateral root development•Bacillolysin interacts with Arabidopsis receptor CEPR2 to mediate IAA34-PUCHI module•Bacillolysin activates downstream LBD33 expression to promote lateral root developmentSummaryLateral roots (LRs) can continuously forage water and nutrients from soil. In Arabidopsis thaliana, LR development depends on a canonical auxin signaling pathway involving the core transcription factors INDOLE-3-ACETIC ACIDs (IAAs) and AUXIN RESPONSE FACTORs (ARFs). In this study, we identified a protein, bacillolysin, secreted by the beneficial rhizobacterium Bacillus velezensis SQR9, that is able to stimulate LR formation of Arabidopsis. The receptor protein kinase C-TERMINALLY ENCODED PEPTIDE RECEPTOR2 (CEPR2) interacts with bacillolysin and plays a critical role in LR development. In the bacillolysin-regulated signaling pathway, the transcriptional repressor IAA34 interacts with PUCHI to activate downstream LATERAL ORGAN BOUNDARIES-DOMAIN33 (LBD33) expression, consequently inducing LR development. This study reveals interkingdom communication via a protein that mediates a novel pathway to induce LR development.Graphical abstract