EAGER: Generating diploid gametes in maize

The large-scale use of hybrid seeds for growing crops over the past century has resulted in a revolution in agriculture. Hybrid seed is a result of cross-pollinating two plant varieties of the same species that differ in their genetic makeup and phenotype traits. These hybrids are selected for genetic configurations that provide favorable phenotype traits or characteristics like higher grain yield, disease tolerance, etc.

However, the large-scale conventional production of hybrid seeds by crossing inbred parent lines/varieties is resource- and labor-intensive, making them expensive and placing limitations on their availability and benefits to farmers. This hurdle could be overcome if hybrid crops can be made to reproduce asexually as clones, which will maintain the favorable set of genes and combinations that result in high yields, for example.

Recently the technology was developed to produce hybrid rice using the asexual method but it has not yet been successfully adapted to maize, a major crop plant in the U.S.A. In this project, new methods will be developed for maize to maintain the hybrid state of the parent chromosomes in the progeny of hybrid plants. The success of these methods will make possible the inexpensive production of high-yielding hybrid seeds from maize.

With the importance of hybrids for maize cultivation, the project is expected to have a large impact on U.S. agriculture.

Asexual reproduction occurs naturally in many flowering plants by a two-step process called diplosporous apomixis: first, the elimination of genetic segregation during meiosis to make clonal gametes, i.e. egg cells and sperm cells containing unreduced and unrecombined parental genomes, and second, the development of the unfertilized egg cells into embryos to produce clonal plants. Previously, synthetic apomixis has been successfully achieved in rice, through genetic manipulations that combined the substitution of mitosis for meiosis in gamete cells together with the induction of parthenogenesis, where a plant produces fruits and seeds from unfertilized eggs.

In maize, efficient parthenogenesis has recently been demonstrated using the method developed for rice. However, the substitution of mitosis for meiosis has not been successful in maize, due to differences between the function of rice and maize genes involved in the meiosis. This project will develop a novel strategy to generate diploid gametes in maize, based on a hypothesis of conservation of cis-regulatory elements of cell division genes in meiosis and mitosis.

The strategy involves editing multiple genes required for cell division and meiosis, as well as the utilization of selected cell division genes from rice. The methods developed in this project, if successful, could be extended to other major crop plants, and potentially adapted to study other cellular processes in plants.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.