9507082 Napoli A contributing factor to the enormous diversity observed for plant form is the outgrowth of lateral buds, and the subsequent formation of a characteristic shoot system. This proposal is a renewal of previous funding supporting a genetic analysis of axillary branching and apical dominance. Previous work demonstrated that sufficient genetic diversity can be induced through mutagenesis in order to make a genetic study of axillary branching possible. Three genetic loci have been identified in Petunia hybrida that control the degree of axillary branching. The recessive alleles condition the phenotypic expression of increased branching potential or decreased apical dominance (dad). The following objectives will be pursued: 1) continued developmental and physiological characterization of dad1 and dad3 mutants, 2) genetic studies to isolate second site suppressors of dad1 and dad3, along with the genetic characterization of suppressor mutants, 3) double mutant and triple mutant analysis employing dad mutants and increased apical dominance mutants, and 4) transposon tagging to clone the dad1 gene. A transposon tagging system using the maize element Dissociation (Ds) has been developed in this laboratory for an inbred genetic line of P. hybrida. The Davis collection contains 159 plants containing independent Ds donor loci. Ds can be transactivated to excise from donor sites at a high frequency in F1 progeny resulting from a cross to provide active transposase from Activator (Ac). Dr. Napoli has analyzed 51 of the Ds donor loci and have demonstrated the occurrence of pre-meiotic events giving rise to germinal excision events. Two donor Ds loci have been mapped to approximately 2.8cM of the dad1 gene. A test cross has been initiated to tag and clone the dad1 gene. ***
