Gametophytes of the fern ceratipteris richardii are either hermaphroditic or male. The primary sex-determining signal in this and many other ferns is antheridiogen, a gibberellin-like pheromone that is secreted by the gametophyte. In its presence, a juvenile gametophyte develops as a male, whereas in its absence, the juvenile develops as a hermaphoxlite. The primary objective of this proposal is to use a combined genetic and molecular approach to understand how antheridiogen governs the sex of the gametophyte of Ceratopteris. The specific objectives are 1) to identify key regulatory genes involved in sex determination by generating and characterizing mutations; and 2) to isolate genes whose expression is altered in response to antheridiogen using a gene expression screen which identifies mRNAs that differ in abundance between two mRNA populations by a subtractive hybridization method; the temporal and spatial patterns of their expression will then be assessed and their function investigated by expressing their antisense cDNA in transgenic plants. %%% This analysis of the sex determining process in Ceratopterts may advance our general understanding of similar processes in higher plants, and will also relate to more general questions concerning hormonal control of genes involved in the reproductive development of all organisms.
