Part 1: Non-technical Seeds provide a significant fraction of the protein and calories in the diets of humans and livestock. Formation of seeds requires specialized cells called gametes that develop within a flower. A mechanistic understanding of how gametes are produced by plants can lead to an improvement of seed quality and quantity in seed crops. This project will elucidate the genes and genetic networks underlying the process of gamete formation occurring within the flower organs. The project will also provide training in plant genetics and development for undergraduate students, graduate students, and postdoctoral researchers. An outreach program with Langston University, a primarily undergraduate and historically black university, will stimulate involvement by minority undergraduate students in plant biology research.
Part 2: Technical Flowering plants produce two types of female gametes, the egg cell and the central cell, that are both specified within a haploid embryo sac which develops following meiosis in an ovule. The egg cell is haploid, specified from a single nucleus at the distal pole of the embryo sac, whereas the central cell is homodiploid, specified by two nuclei, one from each pole of the embryo sac. Double fertilization of the female gametes by pollen results in a seed containing a diploid embryo arising from the egg cell, and a triploid nourishing tissue, the endosperm, arising from the central cell. The molecular mechanisms by which two female gametes with very distinct characteristics are specified have been largely uncharacterized. Previous research has revealed that the CKI1 gene, encoding a histidine kinase activator of the cytokinin signaling pathway, plays a key role in female gamete specification in the model plant Arabidopsis. Loss of CKI1 expression results in conversion of the central cell to an egg cell leading to arrested seed development. Ectopic expression of CKI1 results in conversion of the egg cell to a central cell, producing seeds with dual endosperms and no embryos. These findings, together with observations of CKI1 protein localization in the developing embryo sac, lead to a model by which female gamete specification is controlled by differential expression and localization of CKI1 to the proximal domain of the embryo sac. This project will identify and characterize factors acting upstream and downstream of CKI1 in the female gametophyte. Transcription factors that activate or restrict CKI1 expression will be identified by screens for upstream regulators of CKI1. Candidate regulatory genes will be functionally characterized by genetic analysis. Transcription factors that act downstream of CKI1 to promote central cell fate will be sought by testing expression of candidate genes using mutant response regulators. The project will provide insights into the spatial regulatory networks that specify cell identities in the developing female gametophyte, and the mechanisms underlying the formation of female gametes in flowering plants.
