Molecular and genetic characterization of genes involved in maize cuticular wax biosynthesis
Maize juvenile plants are coated with a complex mixture of lipids that are referred to as cuticular waxes. Cuticular waxes are ubiquitous throughout the plant kingdom and serve a variety of purposes including protection from desiccation, UV radiation, and pathogens. The lipids that compose cuticular waxes are primarily very long chain fatty acids (VLCFAs) and their derivatives such as alcohols, aldehydes, alkanes, ketones, and esters. These lipids are synthesized in the cytosol by the enzyme complex acyl-CoA elongase. Despite intensive efforts, the characterization of the individual proteins of acyl-CoA elongase and the genes encoding these proteins is lacking due to the technical difficulties associated with isolating these proteins as a consequence of their association with the endoplasmic reticulum. Genetic approaches utilizing mutants defective in their ability to elongate fatty acids have however led to the cloning of several genes that encode components of the acyl-CoA elongase. One class of such mutants in maize, the glossy mutants, have defects that led to a visible reduction in the amount of cuticular waxes that accumulate on the surfaces of leaves. Because cuticular waxes are composed of VLCFAs, mutations that block their accumulation may encode components of the acyl-CoA elongase. Molecular characterization of one such mutant, glossy8, has led to the cloning of an acyl-CoA elongase component, specifically, the beta-ketoacyl reductase component. Research presented in this dissertation described the most extensive genetic characterization of the glossy mutants that has been completed to date. The findings include the identification of several novel glossy loci as well as new insights into the composition of cuticular waxes. Further molecular characterization of the genetically defined glossy8 locus (now termed gl8a) has led to the identification of a gl8 paralog (gl8b). Genetic and molecular analyses of these two paralogous genes indicate that they encode partially redundant functions, that are absolutely essential for normal maize development.