Date of Award
Spring 2005
Document Type
Dissertation - Restricted
Degree Name
Doctor of Philosophy (PhD)
Department
Biological Sciences
First Advisor
Dorweiler, Jane
Second Advisor
Schlappi, Michael
Third Advisor
Karrer, Kathleen
Abstract
MADS-box genes are a large group of transcription factors regulating various aspects of development in different species throughout the eukaryotic kingdom. Here I analyze two cases that will further our understanding about the evolutionary significance and the functional diversity of MADS-box genes in plants. Data presented here suggest that a dosage-dependent floral repression mechanism is provided by the Arabidopsis MADS-box floral repressor FLC and its paralogs. Gene duplication is a prevalent phenomenon in the evolution of genomes. Gene duplicates may provide an evolutionary advantage and be preserved in the genome. One mechanism for the preservation of gene duplicates is if they function in an additive way to regulate a quantitative trait. It is shown here that FLC and its duplicates, primarily FCL4 , delay flowering time in Arabidopsis, and their effects are additive and can be attenuated by cold. The conservation and divergence among FLC and its duplicates are also analyzed and their evolutionary significance is discussed. Since FLC homologs have only been found in species of the Brassica family, therefore, floral repression by FLC homologs is suggested to be a unique strategy conserved in these closely related species. Quite opposite to the MADS-box floral repressor FLC , members of the AP1/FUL group of MADS-box genes are found throughout flowering plants, and many are shown to activate the floral transition. In Arabidopsis, AP1 activates the floral development program through specifying the identity of floral meristems. Here, a maize (corn) AP1/FUL gene, zap1 , was analyzed for its function in floral activation. zap1 is downregulated in a late-flowering maize mutant ( mop1 ). Moreover, several putative repressors of zap1 are upregulated in the mop1 mutant. The functional analysis of zap1 in the heterologous system, Arabidopsis, suggested that zap1 activates floral transition. Although the regulation of flowering time is not well characterized in maize, these data suggest that maize AP1/FUL gene zap1 may function as a MADS-domain floral activator. The conservation and divergence of floral regulation between the two systems, the model plant Arabidopsis and the economically important crop maize, is discussed.