Molecular cloning of antheridiogen-induced genes during gametophyte development of the homosporous fern Ceratopteris richardii
Abstract
The gametophytes of the homosporous fern Ceratopteris richardii can be either male or hermaphroditic. The primary sex-determining factor is a plant pheromone known as antheridiogen (A$\sb{\rm CE}$) that is secreted by sexually-determined hermaphrodites. Only during a competent stage of development can antheridiogen induce a single gametophyte to develop as a male. In the absence of A$\sb{\rm CE}$, a single gametophyte will develop as a hermaphrodite. To understand how A$\sb{\rm CE}$ controls the sex of the gametophyte, a PCR-coupled subtractive hybridization approach was used to clone one gene induced by A$\sb{\rm CE}$, named ANI1, as well as five other genes (Hn) that are expressed during male development. The Hn genes are first expressed as antheridia differentiate on the prothallus of the male gametophyte, indicating that they are involved male differentiation. One gene, Hn153, is similar to pectinesterase. The ANI1 gene is expressed earlier in gametophyte development as the sex of the gametophyte is determined. ANI1 shares no significant homology to other genes. The deduced amino acid sequence of ANI1 shows that ANI1 contains two types of amino acid repeats. The protein is predicted to form a $\beta$-barrel with hydrophobic regions positioned inside the barrel, suggesting that ANI1 is a carrier protein of small hydrophobic molecules. The expression of ANI1 in different sex-determining mutant backgrounds indicates that TRA5, a gene required for the female development, encodes a repressor of ANI1 expression. The expression of ANI1 is not affected by other sex-determining mutants tested, suggesting ANI1 regulation may be independent, or up-stream of other genes defining the A$\sb{\rm CE}$ signal transduction genes. Based on these studies, I propose that A$\sb{\rm CE}$ is concentrated and carried by ANI1 and brought to the A$\sb{\rm CE}$ receptor(s) during the brief stage of development that the gametophyte is competent to respond to A$\sb{\rm CE}$. The Hn genes may belong to the class of genes that are activated by the FEM gene and required for the differentiation of male traits. In the absence of A$\sb{\rm CE}$, ANI1 is repressed by TRA5 or genes regulated by TRA5. The TRA genes also repress FEM, the gametophyte will develop female traits.
Degree
Ph.D.
Advisors
Banks, Purdue University.
Subject Area
Molecular biology|Genetics|Botany
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