Poster: Evolution

Abs # 794: The phenotype of Arabidopsis ovule mutants mimic an ancestral reproductive structure: telomes surrounding a sporangium

Presenter:	Hauser, Bernard A., bahauser@botany.ufl.edu
Authors	Hauser, Bernard A. (A)   Park, Sung O. (A)   Hwang, Soon  (A)
Affiliations:	(A): University of Florida

An ovule is the female reproductive structure in angiosperms. It has maternal tissues that surround and nourish the centrally located gametophyte and embryo. Genetic analyses of ovule development identified a number of mutants regulating ovule formation, patterning and morphogenesis. The pretty few seeds2 mutant (pfs2) regulates patterning in ovules. The pfs2 mutant exhibited defects in development of the integuments and female gametophyte. This locus was inherited as a maternal trait; indicating that the defect in gametophyte formation results from alterations in the development of the maternal organs. In pfs2 ovule primordia, the boundary between the nucellus and chalaza, shifted towards the distal end. Based on the phenotypes of single- and double-mutants, the PFS2 locus establishes a field in the chalaza that regulates integument morphogenesis. Interestingly, the phenotype of the pfs2 and inner no outer double mutant had integuments that appear similar to telomes (sterilized sporangia and/or branches surrounding female reproductive structures in fossilized plants). The fossil record indicates that the inner integument evolved from the fusion of telomes. During integument evolution, a signaling system between the central fertile sporangia and the surrounding telomes would need to evolve. The PFS2 locus exhibits some properties of this type of signaling system—it establishes a region for integument initiation and is required for smooth morphogenesis of these structures. Evaluating the function of the PFS2 gene in primitive seed plants might provide insights into integument evolution.