NpCIPK6–NpSnRK1 module facilitates inter-subgeneric hybridization barriers in water lily (nymphaea) by reducing abscisic acid content

Pre-fertilization hybridization barriers are the main causes of inter-subgeneric hybridization challenges in water lily. However, the mechanism underlying low compatibility between pollen and stigma of water lily remains unclear. This study demonstrates that CBL-interacting protein kinase 6 (CIPK6) responded to the signaling exchange between incompatible pollen and stigma through interactions with SNF1-related kinase 1 (SnRK1) and promotes the accumulation of SnRK1 protein. Activated SnRK1 interacted with 9-cis-epoxycarotenoid dioxygenase 2 (NCED2) to promote its degradation, thereby inhibiting abscisic acid (ABA) synthesis. A decrease in ABA content in the stigma impaired the ABA-mediated removal of reactive oxygen species (ROS), ultimately resulting in the rejection of the incompatible pollen by the stigma. Our results highlight the essential role of the NpCIPK6–NpSnRK1–NpNCED2 module in conferring inter-subgeneric hybridization barriers in water lily by interfering with ABA synthesis and promoting ROS accumulation. This study offers valuable mechanistic insights into cellular signaling and reproductive barriers in water lily as well as across other biological contexts.