Water lilies (Nymphaea spp.) are treasured worldwide for their aesthetic, ecological, and medicinal value. Yet breeding new hybrids combining the colorful traits of tropical varieties with the cold resistance of hardy types has proven difficult. For over 150 years, researchers have attempted to cross subgenera but faced challenges primarily due to prefertilization barriers, particularly poor pollen germination on stigmas. Prior studies have implicated abscisic acid (ABA) and reactive oxygen species (ROS) in regulating pollen-stigma interactions, but the precise mechanisms remained unclear. Due to these unresolved challenges, there is a pressing need to investigate the molecular networks that govern stigma receptivity and pollen compatibility in water lilies.
A research team from Nanjing Agricultural University, in collaboration with Hainan University and Guangxi Academy of Agricultural Science, published their findings (DOI: 10.1093/hr/uhae289) on October 23, 2024, in Horticulture Research. Their study, titled "NpCIPK6–NpSnRK1 module facilitates intersubgeneric hybridization barriers in water lily by reducing abscisic acid content," reveals a novel molecular mechanism underlying cross-subgenus incompatibility in water lilies. By dissecting the NpCIPK6–NpSnRK1–NpNCED2 signaling pathway, the researchers offer promising strategies for improving hybridization success.
The study identified NpCIPK6 as a key regulator activated by intersubgeneric hybridization signals in water lily stigmas. NpCIPK6 interacts with NpSnRK1, enhancing its kinase activity and leading to the degradation of NpNCED2, a critical enzyme involved in ABA biosynthesis. Reduced ABA levels in stigmas impair the antioxidant system, causing an accumulation of ROS, which subsequently inhibits the germination of incompatible pollen. Using antisense oligonucleotide technology to knock down NpCIPK6 or NpSnRK1 significantly increased ABA levels, reduced ROS content, and promoted pollen germination, ultimately improving fruit set in intersubgeneric crosses. Additionally, heterologous overexpression experiments in tobacco confirmed that elevated NpCIPK6 and NpSnRK1 suppress pollen germination through ROS accumulation. The research not only clarifies the molecular basis of hybridization barriers in water lilies but also highlights potential genetic targets for facilitating cross-breeding between tropical and hardy varieties. The discovery of this pathway fills a critical gap in understanding plant reproductive isolation mechanisms and provides practical solutions for breeding programs.
"Our research sheds light on a previously unknown molecular barrier that limits cross-breeding in water lilies," said Dr. Yingchun Xu, the corresponding author. "By targeting the NpCIPK6–NpSnRK1–NpNCED2 pathway, breeders could potentially develop strategies to overcome these prefertilization obstacles. This could dramatically expand the genetic diversity of water lilies and produce new cultivars with enhanced traits. Beyond water lilies, these insights may also inspire studies in other species facing similar reproductive challenges."
The elucidation of the NpCIPK6–NpSnRK1–NpNCED2 module offers promising avenues for enhancing intersubgeneric hybridization in water lilies, enabling the creation of cultivars that combine vivid coloration with cold hardiness. By genetically manipulating key components of this pathway or using targeted chemical treatments to regulate ABA and ROS levels, breeders can improve pollination success rates. Furthermore, this study provides a model for investigating reproductive barriers in other ornamental and crop plants, offering new perspectives for overcoming species boundaries and enhancing biodiversity in plant breeding.
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References
DOI
10.1093/hr/uhae289
Original Source URL
https://doi.org/10.1093/hr/uhae289
Funding information
This work was supported by the National Natural Science Foundation of China (grant nos. U1803104 and U2003113), Hainan Natural Science Foundation (grant no. 2021JJLH0031), and Guangxi Natural Science Foundation (grant no. 2022GXNSFBA035635).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.