LAUSR

Fertilization of an egg by multiple sperm (polyspermy) leads to lethal genome imbalance and chromosome segregation defects. In Arabidopsis thaliana, the block to polyspermy is facilitated by a mechanism that prevents polytubey (the arrival of multiple pollen tubes to one ovule). We show here that FERONIA, ANJEA, and HERCULES RECEPTOR KINASE 1 receptor-like kinases located at the septum interact with pollen tube–specific RALF6, 7, 16, 36, and 37 peptide ligands to establish this polytubey block. The same combination of RALF (rapid alkalinization factor) peptides and receptor complexes controls pollen tube reception and rupture inside the targeted ovule. Pollen tube rupture releases the polytubey block at the septum, which allows the emergence of secondary pollen tubes upon fertilization failure. Thus, orchestrated steps in the fertilization process in Arabidopsis are coordinated by the same signaling components to guarantee and optimize reproductive success. Description Block to polyspermy The next generation needs enough, but not too many, nuclear genomes. Zhong et al. show how the small mustard plant Arabidopsis both blocks polyspermy and also adds second-chance insurance when the first fertilization effort goes awry. Signals from the synergid cells in the female gametophyte invite a nearby pollen tube, which secretes peptides to block other pollen tubes from tagging along. The blockade persists as the pollen tube grows to its target. If the pollen tube successfully releases its pair of sperm (plants have a dual fertilization system), the pollen tube’s signaling system fades to silence. If the female gametophyte successfully receives the sperm nuclei, invitational signals from the synergid cells also fade to silence. If, however, fertilization fails, the persistent signal from the synergid cells continues to attract pollen tubes and, because pollen tube rupture silenced the first pollen tube’s block to polytuby, secondary pollen tubes are able to give another try at fertilization. —PJH Signaling between pollen tube and female gametophyte ensures that only one pollen tube gets through but can re-establish access in case of failure.