How the gender of a flower or plant is determined is an important problem in plant developmental biology. Understanding this process also has practical applications in agriculture and plant breeding, as the gender of a flower or plant often limits how it is bred and cultivated. To address this problem, we have used the fern Ceratopteris as a model system. The haploid gametophytes of Ceratopteris are sexually dimorphic, either male or hermaphroditic. The sex of the gametophyte is determined by the gibberellin-like pheromone, antheridiogen, which is secreted by the hermaphrodite and causes sexually immature gametophytes to develop as males. By generating mutations that alter the sex of the gametophyte and by cloning genes that are induced by the pheromone, we have identified more than 15 genes that regulate the sex of the gameotphyte, and defined the sex-determining pathway in this species.
Our present and future research goals are to clone both the antheridiogen signal transduction genes and the master sex regulator genes that ultimately determine the gender of the gametophyte. Once cloned, we will study if and how homologous genes are involved in regulating sex expression in flowering plants, and how these and other genes involved in sexual reproduction evolved during land plant evolution.