Glyoxysomes are specialized peroxisomes that contain enzymes critically required for the mobilization of lipids. To study processes involved in the biogenesis of the organelle, Dr. Harada is investigating the regulation of genes encoding isocitrate lyase and malate synthase, two glyoxylate cycle enzymes that are associated exclusively with glyoxysomes. The genes are regulated developmentally; they are expressed in seedlings, developing seeds, senescent organs, and in pollen but not in non-senescent organs of the mature plant. Moreover, regulation of the genes occurs primarily at the transcriptional level. The proposal's long term goal is to define the physiological signals that regulate these genes, and, therefore, control glyoxysome biogenesis. An accompanying objective is to determine whether a common signal regulates these genes at different periods of the plant life cycle. Two primary approaches are proposed to address these issues. First, Dr. Harada will localize cis-acting elements and identify the DNA binding proteins that interact with these elements to obtain a mechanistic understanding of the regulation of the genes. Second, he will identify mutants altered in the expression of the genes to begin to define components of the pathway regulating the genes. He anticipates that these complementary studies ultimately will provide insight into the physiological cues that control glyoxysome biogenesis.
