The Genetic and Molecular Basis of Sex Determination in Ceratopteris

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AbstractGametophytes of the fern Ceratopteris richardii are sexually dimorphic, either hermaphroditic or male. The determinant of sex in this and other ferns is antheridiogen, a gibberellin-like pheromone that is secreted by the hermaphroditic gametophyte and promotes male development of other sexually undetermined gametophytes. The plant hormone abscisic acid blocks the antheridiogen response. The primary objective of this proposal is to understand how antheridiogen and abscisic acid govern the sex of the Ceratopteris gametophyte. The genetic analysis of five phenotypic classes of sex-determining mutants (12 loci) has led to a hypothetical sex-determining genetic pathway in this species. To understand how these genes regulate sex determination at the molecular level, it will be necessary to clone these genes. The objectives of the proposed research are to continue the genetic analysis of sex determination and develop methods required to clone the sex-determining genes in Ceratopteris. These methods include transformation, which will allow us to incorporate reverse genetic approaches to study gene function, and endogenous transposable element identification, which will provide new options to clone the many genes that have been identified by mutation. Understanding how sex is determined in plants is an important developmental question whose answer may ultimately have practical applications in agriculture and plant breeding. The proposed studies will provide a basic understanding of the genes involved in this process and will also be of value in understanding how the fate of a plant cell (the fern spore) is ultimately regulated by antheridiogen, a gibberellin-like pheromone.