Rice is a crucial staple for over half of the world’s population, yet many farmers cannot afford to grow high-yielding varieties due to the high cost of seeds. A team of researchers from the University of California (UC), Davis, and Berkeley, has developed a promising solution that could lower costs and boost rice production.
The breakthrough involves activating two genes in rice egg cells that prompt their development into embryos without fertilization. This process could create high-yielding clonal strains of rice, allowing for more efficient and cost-effective farming.
The team, led by Venkatesan Sundaresan, a Distinguished Professor of Plant Biology and Plant Sciences at UC Davis, previously demonstrated that the BBM1 gene could trigger embryo formation in rice egg cells. However, this method was only successful 30% of the time. Now, in collaboration with UC Berkeley’s Innovative Genomics Institute, the team has discovered that activating a second gene, WOX9A, boosts the success rate to approximately 90%. The findings were published in Nature Plants.
Sundaresan expressed optimism about the progress, noting, “After 20 years of failed attempts in clonal hybrids, this is a significant leap forward. We are now closer than ever to achieving sustainable agriculture with high yields globally.”
A More Affordable Way to Feed the World
Hybrid rice varieties, which yield up to twice the amount of regular crops, are highly beneficial. However, they are expensive to produce, requiring farmers to purchase new seeds each year. The ability for hybrid rice to reproduce asexually would allow farmers to save seeds, cutting costs significantly. For over 30 years, scientists have struggled to develop a way to make rice plants reproduce without fertilization.
In earlier research, Sundaresan’s team showed that activating BBM1 in rice egg cells could bypass the need for fertilization. However, this process only worked one-third of the time. The team hypothesized that BBM1 alone might not be enough, and that additional support was needed.
By analyzing gene expression in fertilized rice eggs, they identified WOX9A, a gene that is typically only activated by the sperm. When both BBM1 and WOX9A were activated together in egg cells, embryo formation occurred 90% of the time. However, activating WOX9A alone did not initiate embryo formation.
Sundaresan explained, “BBM1 primes the egg cell to become an embryo, but it needs WOX9A to ensure that the process continues and doesn’t reverse.”
Achieving Hybrid Vigor Without Hybrids
The plants produced by this method are haploids, meaning they carry half the usual number of chromosomes. While these plants do grow, they are generally smaller than diploid plants, which contain two sets of chromosomes.
Imtiyaz Khanday, a co-author of the study and assistant professor at UC Davis, explained, “Haploids are valuable for breeding pure lines, ensuring uniform crops. This method also allows for the high-frequency production of clonal seeds, preserving hybrid vigor.”
Looking ahead, the researchers plan to combine this technique with “synthetic apomixis”—a process they developed that enables asexual seed production. By combining both methods, farmers could repeatedly harvest high-yielding hybrid seeds from saved crops.
Sundaresan concluded, “By turning egg cells into embryos without fertilization and combining this with a technique to eliminate meiosis, we can create high-yielding hybrid seeds. This innovation offers a sustainable path forward for rice farmers and could extend to other crops in the future.”
Additional authors of the study include Hui Ren and Kyle Shankle from UC Davis, as well as Myeong-Je Cho and Michelle Tjahjadi from UC Berkeley.
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