Functional Analyses of APETALA3-Like Genes

Yale University, New Haven CT

Investigators

Abstract

0110731 Irish Flowers are a defining characteristic of the angiosperms, yet there is wide variation in floral form. Based on results from Arabidopsis and several other higher eudicot species, it has been proposed that, despite the wide variation in floral architecture, the molecular mechanisms controlling floral development are conserved across all angiosperms. This hypothesis, however, has not been critically tested. One key regulatory gene, the floral homeotic APETALA3 (AP3) gene, has been shown to be required for specifying petals and stamens in the higher eudicot Arabidopsis. The experiments described will address the larger question of whether the molecular mechanisms controlling floral development are conserved or have diverged by investigating the functions of AP3-like genes in other angiosperm species. These studies will be carried out in tomato and in opium poppy. Phylogenetic analyses indicate that a duplication event in the AP3 lineage occurred at the base of the higher eudicots, leading to two AP3-like lineages in these species: the euAP3 lineage and the TM6 lineage. To date, all functional analyses have focussed on the role of the euAP3 lineage genes, of which the Arabidopsis AP3 gene is a member. The roles of the paralogous TM6 lineage genes are currently unknown and will be addressed by carrying out functional studies in tomato, a species for which a number of genetic and molecular tools exist. These investigations will include screening for insertional mutations in the TM6 gene, transgenic manipulation of the TM6 gene, and genetic experiments utilizing a previously identified tomato AP3 insertional mutation. The lower eudicots and basal angiosperms contain only one AP3-like lineage. These genes are more similar in sequence to the higher eudicot TM6 genes and are termed the paleoAP3 lineage genes. The function of a paleoAP3 lineage member will be investigated using opium poppy as a model system. These studies will include cloning and characterizing the opium poppy paleoAP3 gene and determining whether any of the previously identified poppy floral homeotic mutations correspond to lesions in this gene. In addition, expression studies will be carried out in order to characterize the processes controlling floral development in this species. The results obtained from these studies will be valuable in shedding light on how gene duplication and diversification are related to changes in gene function. They will also provide a basis for developing new and more rigorous hypotheses to explain, at the molecular genetic level, how morphological innovations in floral form have arisen.