Glucose signal transduction and the role of the HD2 family of histone deacetylases in Arabidopsis seedling germination and development

Histone deacetylases (HDACs) are an essential class of enzyme that are required by eukaryotic organisms for the coordinated expression of genes. They therefore play key roles in cell differentiation and organ development through global gene regulation. The HD2 sub-family of HDACs are unique to the plant kingdom. Arabidopsis thaliana contains four members of the HD2 family known as HD2A, HD2B, HD2C, and HD2D. A prior thesis by Adam Colville identified the induction of HD2 transcripts in response to glucose, sucrose and fructose.;Phenotypic analysis of hd2 mutants suggested functional specialization among the HD2 members in embryo development and seed germination. HD2A and HD2C play opposite roles in the control of seed germination.;This study reveals functional differences among the HD2 family members, and provides new insights into the mechanisms that govern control of HD2 gene expression and the role that this novel gene family performs in plant development.;Using quantitative real-time PCR, the results of my study indicate that the induction of HD2 expression by glucose, sucrose and fructose is specific to the HD2A and HD2D members in the wild-type background. Using a hexokinase null mutant in the signaling, gin2-1, the glucose-HD2 induction pathway was found to be mediated by a hexokinase-independent pathway. The induction of HD2A and HD2D by glucose may occur directly at the promoter through motifs that have been identified previously in the promoters of glucose responsive genes.