Hormonal and transcriptomic analysis reveals the role of ABA and BR in breaking the barrier of inter-subgeneric hybridization in water lily (Nymphaea)

Understanding the process of signal communication between pollen and stigma is of significant importance for plant sexual reproduction. In the case of inter-subgeneric hybridization in water lily, there exists a pre-fertilization hybridization barrier, the regulatory mechanism of which remains unclear. In this study, we conducted hormone and transcriptome analyses of unpollinated stigmas (Mock), self-pollinated stigmas (SP), cross-pollinated stigmas within the same subgenus (CP), and inter-subgenus cross-pollination stigmas (ISCP) in water lily to elucidate the formation mechanism of the inter-subgeneric hybridization barrier. Our results indicated that the lack of ABA and BR in ISCP stigmas are key factors contributing to the formation of the inter-subgeneric hybridization barrier in water lily. Exogenous application of ABA and BR can help overcome the barrier between inter-subgeneric water lily crosses. Through transcriptome analysis, we identified nine candidate genes involved in regulating the inter-subgeneric hybridization barrier in water lily. In addition, we further demonstrated the importance of the NCED2-mediated ABA synthesis pathway in the hybridization process through AS-ODN technology. Our study confirms that ABA and BR are critical for breaking the inter-subgeneric hybridization barrier in water lily. The identification of the nine candidate genes provides important clues for further research on the hybridization recognition mechanism in water lily.