Ph.D Indiana University, 1979
306 Manter Hall
I have been interested in gene structure and function in plants. Much of the work I have done in the past used maize Adh genes as a model for gene structure and function. For the past three years Dr. John Markwell from the Biochemistry Department and myself have been working on single carbon metabolism in plants and how this pathway responds to stress. My interests in this system started with the work I did related to characterization of formaldehyde dehydrogenase genes in Arabidopsis and rice. This enzyme is related to alcohol dehydrogenase in plants in terms of protein domains and catalytic function. Gene structure is also conserved. The enzyme is part of the single carbon metabolic pathway that serves as a carbon dissimilation pathway. Starting with 10-formyltetrahydrofolate synthetase (THF) production of formaldehyde, which is converted to formate by formaldehyde DH. Formate dehydrogenase then converts this to carbonate that can be removed by gas exchange. We have cloned and sequenced the Arabidopsis genes for formate DH and THF. We have used these sequences as probes for expression in Arabidopsis and other plants. These genes can be induced by foliar application of single carbon molecules such as formate or methanol. When these plants are also under water limitation, they can maintain biomass compared with untreated controls. This is observable in C3 but not C4 plants suggesting some interaction with photorespiration. Our hypothesis is that the single carbon compounds can induce this carbon dissimilation pathway and, under water limitation, some of the CO2 produced by photorespiration could be recaptured by this pathway assimilating the carbon. We are in the process of creating transgenic plants altered in the expression of these genes to examine the physiology of this pathway.
In characterizing the formate DH we discovered that the enzyme has the targeting sequences for both mitochondria and chloroplasts. This has been observed for some tRNA synthetases in Arabidopsis but the formate DH for other plants is mitochondrial. We are in the process of demonstrating the co-localization by using fusion proteins and immunolocalization. We are planning to examine the properties of the dual signal by in vitro mutagenesis and to use expression mutants to examine the role of the enzyme in the chloroplast.
This pathway occurs in some bacteria as a carbon assimilatory pathway. In plants it has been adapted to dissimilate carbon instead. By comparing the use of this pathway in related taxa we may uncover the evolution of this adaptation. This work has applied implications for the development of drought resistance in plants. Genetic manipulation of this pathway may increase the yield potential of plants grown under water-limited conditions.