A receptor–channel trio conducts Ca 2+ signalling for pollen tube reception

Precise signalling between pollen tubes and synergid cells in the ovule initiates fertilization in flowering plants 1 . Contact of the pollen tube with the ovule triggers calcium spiking in the synergids 2 , 3 that induces pollen tube rupture and sperm release. This process, termed pollen tube reception, entails the action of three synergid-expressed proteins in Arabidopsis : FERONIA (FER), a receptor-like kinase; LORELEI (LRE), a glycosylphosphatidylinositol-anchored protein; and NORTIA (NTA), a transmembrane protein of unknown function 4 – 6 . Genetic analyses have placed these three proteins in the same pathway; however, it remains unknown how they work together to enable synergid–pollen tube communication. Here we identify two pollen-tube-derived small peptides 7 that belong to the rapid alkalinization factor (RALF) family 8 as ligands for the FER–LRE co-receptor, which in turn recruits NTA to the plasma membrane. NTA functions as a calmodulin-gated calcium channel required for calcium spiking in the synergid. We also reconstitute the biochemical pathway in which FER–LRE perceives pollen-tube-derived peptides to activate the NTA calcium channel and initiate calcium spiking, a second messenger for pollen tube reception. The FER–LRE–NTA trio therefore forms a previously unanticipated receptor–channel complex in the female cell to recognize male signals and trigger the fertilization process.