<i>Arabidopsis</i> glycosylphosphatidylinositol-anchored protein LLG1 associates with and modulates FLS2 to regulate innate immunity.

Abstract

Plants detect and respond to pathogen invasion with membrane-localized pattern recognition receptors (PRRs), which recognize pathogen-associated molecular patterns (PAMPs) and activate downstream immune responses. Here we report that <i>Arabidopsis thaliana</i> LORELEI-LIKE GPI-ANCHORED PROTEIN 1 (LLG1), a coreceptor of the receptor-like kinase FERONIA, regulates PRR signaling. In a forward genetic screen for suppressors of <i>enhanced disease resistance 1</i> (<i>edr1</i>), we identified the point mutation <i>llg1-3</i>, which suppresses <i>edr1</i> disease resistance but does not affect plant growth and development. The <i>llg1</i> mutants show enhanced susceptibility to various virulent pathogens, indicating that LLG1 has an important role in plant immunity. LLG1 constitutively associates with the PAMP receptor FLAGELLIN SENSING 2 (FLS2) and the elongation factor-Tu receptor, and forms a complex with BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED RECEPTOR KINASE 1 in a ligand-dependent manner, indicating that LLG1 functions as a key component of PAMP-recognition immune complexes. Moreover, LLG1 contributes to accumulation and ligand-induced degradation of FLS2, and is required for downstream innate immunity responses, including ligand-induced phosphorylation of BOTRYTIS-INDUCED KINASE 1 and production of reactive oxygen species. Taken together, our findings reveal that LLG1 associates with PAMP receptors and modulates their function to regulate disease responses. As LLG1 functions as a coreceptor of FERONIA and plays central roles in plant growth and development, our findings indicate that LLG1 participates in separate pathways, and may suggest a potential connection between development and innate immunity in plants.