Pectin Methylesterase Regulates Pollen Germination on Stigma after Pollination in Water Lily

Background: In the process of interspecific crossing of water lily, the crossing barrier before fertilization is the main reason for the poor seed setting rate of cross breeding, but the specific mechanism is still unclear. The key regulatory genes involved in the interaction between pollen and stigma at 6 h after cross-pollination and self-pollination in water lilies were studied. Results: Feronia (FER) receptor kinase and respiratory burst oxidase homologue D (RbohD) gene in the regulation pathway of reactive oxygen species (ROS), Calcineurin B-Likes (CBLs), CBL-Interacting protein kinases (CIPKs) and Calcium-dependent protein kinase (CDPKs) in Ca2+signal, and pectin methylesterase (PME) genes may play a key role in the process of mutual recognition between pollen and stigma after cross-pollination of water lilies, which needs further research. Conclusions: We infer that after cross-pollination, the expression levels of reactive oxygen species and a certain target protein in the stigma papilla cells of water lilies increase through Ca2+ receptors. The target protein alone or together with ROS regulates the increase of PME activity, thus increasing the hardness of the cell wall of the stigma papilla cells and making it difficult for pollen tubes to enter the stigma papilla cells.