Conserved role of the SERK–BIR module in development and immunity across land plants

Abstract

SummarySOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASES (SERKs), which are subfamily II of leucine-rich repeat receptor-like kinases (LRR-RLKs), play diverse roles in development and immunity in the angiospermArabidopsis thaliana. AtSERKs act as co-receptors for many LRR-RLKs, including BRASSINOSTEROID INSENSITIVE 1 (BRI1) and FLAGELLIN SENSITIVE 2 (FLS2).1–4The conserved tyrosine (Y) residue in AtSERK3 is crucial for signaling specificity in differentiating BRI1- and FLS2-mediated pathways.5BRI1-ASSOCIATED RECEPTOR KINASE 1 (BAK1)-INTERACTING RECEPTOR-LIKE KINASES (BIRs) interact with SERKs under resting conditions, negatively regulating SERK-mediated pathways.6,7SERK and BIR are highly conserved in land plants, whereas BRI1 and FLS2 homologs are absent or poorly conserved in bryophyte lineages.8,9The biological functions of SERK homologs in non-flowering plants are largely unknown. The genome of the liverwortMarchantia polymorphaencodes single homologs for SERK and BIR, namely MpSERK and MpBIR.9We here show that Mpserkdisruptants display growth and developmental defects with no observable sexual or vegetative reproduction. Complementation analysis revealed a contribution of the conserved Y residue of MpSERK to growth. Proximity labelling-based interactomics identified MpBIR as a MpSERK interactor. Mpbirdisruptants displayed defects in reproductive organ development. Patterns of development- and immunity-related gene expression in Mpserkand Mpbirwere antagonistic, suggesting that MpBIR functions as a MpSERK repressor. The pathogenic bacteriumPseudomonas syringaepv.tomatoDC3000 grew poorly on Mpbir, indicating a significant role of the MpSERK1MpBIR module in immunity. Taken together, we propose that the SERK–BIR functional module was already regulating both development and immunity in the last common ancestor of land plants.