Researchers Uncover Water Lily Hybridization Secrets Using NpCIPK6

Researchers at Nanjing Agricultural University have made significant strides in understanding the hybridization barriers faced by water lilies, a challenge that has long hindered efforts to create new varieties. Their study, published on October 23, 2024, in the journal Horticulture Research, highlights the critical roles of the proteins NpCIPK6 and NpSnRK1 in overcoming these barriers. Hybridization between hardy and tropical water lilies has been complicated by pre-fertilization obstacles, particularly issues related to pollen viability.

The research indicates that one of the main issues affecting successful hybridization is the poor germination of pollen and abnormal growth of pollen tubes. While abscisic acid (ABA), a plant hormone, is known to influence pollen viability, its specific role in hybridization barriers had remained unclear until now. The study reveals how the interaction between NpCIPK6 and NpSnRK1 affects ABA synthesis and the accumulation of reactive oxygen species (ROS), which are crucial for pollen germination.

Unveiling the Molecular Mechanisms

Focusing on the NpCIPK6 – NpSnRK1 signaling pathway, the team discovered that NpCIPK6 plays a vital role in regulating hybridization barriers. When activated by signals from intersubgeneric hybridization, NpCIPK6 enhances the kinase activity of NpSnRK1. This interaction leads to the degradation of NpNCED2, a key enzyme in ABA biosynthesis, resulting in reduced ABA levels in the stigma. Lower ABA levels in turn impair the removal of ROS, which is responsible for preventing the germination of incompatible pollen.

Interestingly, the study found that knocking down either NpCIPK6 or NpSnRK1 resulted in increased ABA content in the stigma, which facilitated pollen germination on stigmas that would otherwise be incompatible. This indicates that manipulating the NpCIPK6 – NpSnRK1 pathway could enhance fruit set in intersubgeneric crosses, providing practical applications not only in water lily breeding but potentially in other crops facing similar reproductive challenges.

Implications for Plant Breeding

The findings from this research open new avenues for addressing hybridization barriers in various plant species. As Dr. Yingchun Xu, a leading researcher in the study, noted, “This discovery sheds light on the complex signaling mechanisms that govern hybridization barriers in water lilies. Understanding the NpCIPK6 – NpSnRK1 pathway not only advances our knowledge of plant reproductive biology but also opens up new possibilities for overcoming hybridization barriers in other plant species.”

The implications are far-reaching. By targeting the NpCIPK6 – NpSnRK1 signaling pathway, scientists may enhance hybridization success across a range of plants, leading to the development of new cultivars with improved traits, such as enhanced color variation, cold resistance, and better adaptability to environmental changes. This research also contributes to a broader understanding of plant hormonal regulation, which is crucial for crop improvement, conservation efforts, and ecological restoration initiatives.

This study was supported by the National Natural Science Foundation of China (grants U1803104 and U2003113), the Hainan Natural Science Foundation (grant 2021JJLH0031), and the Guangxi Natural Science Foundation (grant 2022GXNSFBA035635).

For those interested in the detailed findings, the full study can be accessed through this DOI: 10.1093/hr/uhae289.