Parallel CLE peptide signaling pathways control nodulation in pea

Legume root nodulation with nitrogen-fixing bacteria requires precise control via root-shoot-root autoregulation of nodulation (AON). Post-translationally modified root-derived CLAVATA3/Embryo Surrounding Region-Related (CLE) peptides signal through shoot acting leucine-rich repeat receptors (CLAVATAs) to regulate nodule number and this pathway is a target to optimise nodulation. We characterise the AON system in the crop model pea ( Pisum sativum L.) and address key gaps in our understanding of AON; the role of parallel signalling pathways, shoot receptor complexes and downstream targets. We use novel mutant combinations, overexpression, grafting, gene expression and careful analysis of infection and nodule organogenesis using GFP-labelled rhizobium. These studies provide evidence that in pea both Ps CLE12 and Ps CLE13 require arabinosylation via Ps RDN1. Perception of Ps CLE12 and Ps CLE13 in the shoot to suppress the mature nodules in the root requires the pea CLAVATA1 orthologue Ps NARK and Ps CLV2. However, we found little evidence that Ps CLE12 and Ps CLE13 suppress infection thread development or that they act via Ps TML1 and/or Ps TML2, root acting suppressors of nodulation, indicating a role for additional CLE signals. Grafting and double mutant studies indicate that Ps NARK can act together with Ps CLV2, but also independently, to influences nodulation providing in planta evidence for shoot receptor complexes that control AON.