|
Assistant Professor 308 Latham Hall (0390) Phone: (540) 231-7867
|
Experience|
Teaching Interests|
Research Support|
Selected Publications
1. Regulation of seed metabolism
Seeds represent both the first and the last stages of the plant life cycle. During their development they make and store the lipid, protein, and carbohydrate reserves on which humankind depends. Seed composition differs greatly among plant species and varieties, indicating that there is a wide range of metabolic flexibility. However the regulation of storage compound accumulation during seed filling is poorly understood. The long-term goal of my laboratory is to understand the basis of this variability and flexibility in the weed Arabidopsis thaliana and to use this knowledge to alter seed composition in soybean, canola, and peanut to our advantage.
Transcription factors (TFs) play key regulatory roles in all cellular processes, including those leading to seed storage compounds. Because they regulate the expression of multiple genes, TF's have the potential to regulate the flux through whole pathways. My current goal is to identify and characterize TFs involved in the regulation of storage reserve buildup in Arabidopsis seeds using a combination of molecular, biochemical, and computational biology approaches. To accomplish this goal, we take advantage of our recently developed system of cultured Arabidopsis embryos. This system is amenable to high throughput approaches for screens to identify TF mutants affected in seed composition. It closely mimics in planta embryo development, and allows the use of specific labeled precursors for metabolic flux analysis (MFA). Metabolic fluxes define the functional biochemical phenotype of the cell, and understanding how these fluxes are regulated is the key to rational metabolic engineering. MFA is a powerful toolset for quantifying fluxes and has already proven useful in revealing new aspects of seed metabolism. Therefore, MFA is used in collaboration with Dr. Yair Shachar-Hill at Michigan State University as a tool to functionally characterize mutants in TFs involved in the regulation of seed metabolism and composition.
2. Folate inter-conversions in plants
Folates, also known as Vitamin B9, are crucial for normal growth and neural function in animals by being involved in the metabolism of purines and various amino acids. Folates are mediators of one-carbon metabolism as they transfer one-carbon units (methyl, formyl, and others) to the target molecules. Folates exist in various oxidation states and as such, they can be converted to each other enzymatically or by pH changes. Using various mutants in Arabidopsis affected in folate inter-conversion enzymes, we showed that some of these enzymes are involved in photorespiration (a consequence of oxygen fixation by the key photosynthetic enzyme ribulose-1,5-bisphosphate carboxylase/ oxygenase; Rubisco). Folates are cofactors of glycine decarboxylase (GDC) and serine hydroxymethyltransferase (SHMT) that metabolize glycine produced in photorespiration. As these enzymes are folate dependent, they are be inhibited by 5-formyl tetrahydrofolate (5-CHO THF), one of the products of folate inter-conversion. The roles of this inhibitor are not known in animals and plants, but 5-CHO THF may be involved in the regulation of one-carbon metabolism, rather than serve as a donor of one-carbon units. My future research will pursue the basic questions about the roles of this compound in plants.
Mitochondrial folate inter-conversion in plants and photorespiration. Well-established pathways in photorespiration are shown in black, while folate inter-conversion is shown in red. Mutants in 10-FDF and 5-FCL accumulate 5-CHO THF, an inhibitor of GDC and SHMT, and show various degrees of photorespiratory phenotypes (e.g. accumulation of glycine). The DHC mutant does not show any adverse phenotypes as the route to 5-CHO THF is blocked. Crossing the 10-FDF with the DHC mutant saves the 10-FDF mutant, indicating that all phenotypes associated with the 10-FDF mutation are due to inhibition of the GDC/SHMT complex by 5-CHO THF. Abbreviations: DHC, 5,10-methylene THF dehydrogenase/5,10-methenyl THF cyclohydrolase; 5-FCL, 5-formyl THF cycloligase; 10-FDF, 10-formyl THF deformylase; FDH, formate dehydrogenase
