Periodic Reporting for period 1 - HybridSeed (Sex determination genes as a toolbox for F1 hybrid seed production and yield increase)
Reporting period: 2024-01-01 to 2025-06-30
How the gender of a flower or plant is determined is an important question in plant developmental biology. Understanding this process has also practical applications, as the gender of a flower or plant determines how it is bred and cultivated. In particular, one of the remaining challenges in plant breeding is to optimize the production of F1 hybrid seeds in many crops.
F1 hybrid cultivars have made major contributions to the world's food supply. In many cases, hybrid varieties have much superior performance in grain, fruit yield or biomass. The production of F1 hybrid seeds requires controlled pollination to ensure that the seed indeed results from crossing, but not from self-fertilization. To this end, the female parental line that will produce the hybrid seeds should carry strictly female flower to avoid self-pollination. On the other hand, the male line must produce enough pollen. In most crops, producing pure female plants is a challenge that often requires the tedious hand emasculation of bisexual flowers by a skilled workforce. This process is only applicable on a small scale and usually associated with high abortion rates.
The majority of flowering plants are hermaphrodites, producing only bisexual flowers. However, about 10% of species, among which major crops such as maize and cucumber display different sexual morphs. Monoecious species exhibit male and female flowers on the same plant while dioecious species have separate male and female individuals. Gynoecious plants bear only pistillate flowers, androecious ones only staminate flowers. Andromonoecious plants exhibit both male and bisexual flowers.
The Cucurbitaceae family is in the top list for the number of species consumed as human food and used for cultural, medicinal, and botanical purposes. Melon, cucumber, watermelon and zucchini are broadly cultivated in western countries. In total, 34 species are cultivated worldwide. Most of them are monoecious or andromonoecious. Thus, it is not possible to use of two mutually exclusive sexual morphs for F1 hybrid production and the process requires hand emasculation and hand pollination of the female parental line.
The foundation of HybridSeed is the knowledge of how unisexual and hermaphrodite flowers develop, which was built during the previous ERC-funded project, SEXYPARTH. In that research, key genes involved in flower sex determination were identified: CmWIP1, a zinc finger transcription factor that causes gynoecy; CmACS-7, involved in ethylene production and controlling andromonoecy; CmACS11, linked to androecy; and CmHB40, responsible for a second form of andromonoecy.
The HybridSeed project set out to solve major challenges in producing F1 hybrid seeds in cucurbit crops like melon and cucumber. Traditional seed production methods depend on manual flower emasculation and controlled pollination, which are labor-intensive, expensive, and often unreliable due to unstable flower development in parent plants. To address this, HybridSeed developed a new approach using sex determination genes to create female-only (gynoecious), male-only (androecious) and bisexual (hermaphroditic) plants. These modified plants were investigated to ease hybrid seeds production, while maintaining important fruit traits like shape and size.
F1 hybrid cultivars have made major contributions to the world's food supply. In many cases, hybrid varieties have much superior performance in grain, fruit yield or biomass. The production of F1 hybrid seeds requires controlled pollination to ensure that the seed indeed results from crossing, but not from self-fertilization. To this end, the female parental line that will produce the hybrid seeds should carry strictly female flower to avoid self-pollination. On the other hand, the male line must produce enough pollen. In most crops, producing pure female plants is a challenge that often requires the tedious hand emasculation of bisexual flowers by a skilled workforce. This process is only applicable on a small scale and usually associated with high abortion rates.
The majority of flowering plants are hermaphrodites, producing only bisexual flowers. However, about 10% of species, among which major crops such as maize and cucumber display different sexual morphs. Monoecious species exhibit male and female flowers on the same plant while dioecious species have separate male and female individuals. Gynoecious plants bear only pistillate flowers, androecious ones only staminate flowers. Andromonoecious plants exhibit both male and bisexual flowers.
The Cucurbitaceae family is in the top list for the number of species consumed as human food and used for cultural, medicinal, and botanical purposes. Melon, cucumber, watermelon and zucchini are broadly cultivated in western countries. In total, 34 species are cultivated worldwide. Most of them are monoecious or andromonoecious. Thus, it is not possible to use of two mutually exclusive sexual morphs for F1 hybrid production and the process requires hand emasculation and hand pollination of the female parental line.
The foundation of HybridSeed is the knowledge of how unisexual and hermaphrodite flowers develop, which was built during the previous ERC-funded project, SEXYPARTH. In that research, key genes involved in flower sex determination were identified: CmWIP1, a zinc finger transcription factor that causes gynoecy; CmACS-7, involved in ethylene production and controlling andromonoecy; CmACS11, linked to androecy; and CmHB40, responsible for a second form of andromonoecy.
The HybridSeed project set out to solve major challenges in producing F1 hybrid seeds in cucurbit crops like melon and cucumber. Traditional seed production methods depend on manual flower emasculation and controlled pollination, which are labor-intensive, expensive, and often unreliable due to unstable flower development in parent plants. To address this, HybridSeed developed a new approach using sex determination genes to create female-only (gynoecious), male-only (androecious) and bisexual (hermaphroditic) plants. These modified plants were investigated to ease hybrid seeds production, while maintaining important fruit traits like shape and size.
We engineered induced alleles in different component of the sex determination pathway and analysed their impact on sex transition and stability. By combining different versions (alleles) of these genes, we engineered various plant lines and tested their performance under greenhouse conditions. Through genetic characterisation of sex determination pathway, we identified a new gene that enhance gynoecy stability.
The best-performing gene, and allele combinations were used to produce F1 hybrid seeds. These seeds were tested for purity using molecular markers specific to each parent line. Fully hermaphroditic plants were also produced, and assessed for fruit traits. In cucumber, hermaphroditic plants performed especially well, producing more fruits per plant because they could self-pollinate. In melon, the resulting andromonoecious plants showed no changes in fruit shape, as confirmed by measurements of shape and ovary indices. This was a significant achievement, as previous efforts to alter flower sex frequently led to undesirable modifications in fruit appearance.
The best-performing gene, and allele combinations were used to produce F1 hybrid seeds. These seeds were tested for purity using molecular markers specific to each parent line. Fully hermaphroditic plants were also produced, and assessed for fruit traits. In cucumber, hermaphroditic plants performed especially well, producing more fruits per plant because they could self-pollinate. In melon, the resulting andromonoecious plants showed no changes in fruit shape, as confirmed by measurements of shape and ovary indices. This was a significant achievement, as previous efforts to alter flower sex frequently led to undesirable modifications in fruit appearance.
The HybridSeed project achieved its objectives by identifying a new key gene involved in sex determination and uncovering critical alleles that modify sexual morphs. Building on this foundation, the project established an innovative and cost-effective strategy for producing F1 hybrid seeds using genetically induced new sexual morphs. Central to this breakthrough was the use of a novel genetic approach combining gynoecy and dominant hermaphroditism. Our integrated solution directly addressed key genetic, agronomic, and economic barriers in hybrid seed production. It eliminates the need for manual flower emasculation and allows hybrid seeds to be produced naturally through insect pollination. Importantly, this was achieved without compromising essential commercial traits, such as fruit shape. Yield evaluations confirmed significant performance benefits, especially in cucumber, where hermaphroditic plants produced more fruits per plant.
By offering a new tool kit of genes and alleles modifying sexual morphs, our research established a new benchmark in precision breeding for cucurbits. Our strategy has the potential to be extended to other crops where control of floral sex is a breeding priority. This elevates HybridSeed beyond a technical innovation to a transformative breeding strategy with broad applicability across the seed industry.
The project's scientific advances are underpinned by robust intellectual property protection, most notably the patent titled Identification of a New Gene Involved in Sex Determination in Cucurbitaceae (US20240206413A1). This patent not only secures the novelty of the findings but also enhances the project's potential for adoption in commercial breeding programs. The strong results and scalable nature of the technology demonstrate that HybridSeed is not only a valuable tool for modern plant breeding, but a groundbreaking innovation poised to transform hybrid seed production in cucurbits and beyond.
By offering a new tool kit of genes and alleles modifying sexual morphs, our research established a new benchmark in precision breeding for cucurbits. Our strategy has the potential to be extended to other crops where control of floral sex is a breeding priority. This elevates HybridSeed beyond a technical innovation to a transformative breeding strategy with broad applicability across the seed industry.
The project's scientific advances are underpinned by robust intellectual property protection, most notably the patent titled Identification of a New Gene Involved in Sex Determination in Cucurbitaceae (US20240206413A1). This patent not only secures the novelty of the findings but also enhances the project's potential for adoption in commercial breeding programs. The strong results and scalable nature of the technology demonstrate that HybridSeed is not only a valuable tool for modern plant breeding, but a groundbreaking innovation poised to transform hybrid seed production in cucurbits and beyond.