Species-specific interaction of EA1 with the maize pollen tube apex

The egg apparatus-secreted polymorphic EA1 peptide is required for micropylar pollen tube (PT) guidance in maize, the last step of the PT journey during the double fertilization process in flowering plants. In a recent study we have shown that maize PTs are attracted in vitro by EA1 and that their growth is arrested at high peptide concentrations. Moreover, we have also shown that maize PTs are guided in vitro in a species-preferential manner to the micropylar opening of transgenic Arabidopsis ovules secreting the EA1-GFP fusion protein. In support of these findings, we have improved the ligand-receptor labeling assay and report here that the EA1 peptide interacts in vitro with the maize PT apex in a species-specific manner. Bound peptide gets internalized in large vesicles and is degraded. This finding indicates that the pollen tube remains sensitive to the attractant by its rapid internalization.