Prenylcysteine Metabolism and Phytohormone Signaling in Arabidopsis

Indiana University, Bloomington IN

Investigators

Abstract

In plant and animal cells, proteins must be delivered to appropriate sites of action and often must interact with other proteins for normal function. Protein prenylation, the attachment of an isoprenoid lipid to a protein, is one mechanism by which proteins are targeted to appropriate sites and/or modified for interaction with other proteins. While this process has been studied in detail, the degradation of prenylated proteins and the fate of the isoprenoid lipid have not been described in plants. The degradation of prenylated proteins results in the release of a prenylcysteine (i.e., either farnesylcysteine or geranylgeranylcysteine) with the isoprenoid attached to the amino acid cysteine via thioether linkage. Prenylcysteine metabolism in plants is important, at least in part, because prenylcysteine compounds cause an enhanced response to the plant hormone abscisic acid (ABA). This project will examine the farnesylcysteine lyase enzyme that metabolizes farnesylcysteine to farnesal and cysteine in the cruciferous plant Arabidopsis thaliana. A gene on chromosome 5 of the Arabidopsis genome encodes this enzyme and mutations in this gene cause an enhanced response to ABA, presumably because of farnesylcysteine accumulation. This project will also examine the metabolism of geranylgeranylcysteine, which proceeds by a different mechanism. Thus, plants possess at least two distinct mechanisms for prenylcysteine metabolism, one for farnesylcysteine and one for geranylgeranylcysteine, and these processes are required for normal ABA responsiveness. To test the hypothesis that the enzymes involved in prenylcysteine metabolism are important for isoprenoid salvage and detoxification and to describe in detail the role of prenylcysteine metabolism in ABA signaling, biochemical analyses on Arabidopsis prenylcysteine metabolic enzymes will be performed and the corresponding genes identified. In addition, the subcellular locations of Arabidopsis prenylcysteine metabolic enzymes and the phenotypes of Arabidopsis plants deficient in prenylcysteine metabolic enzymes will be analyzed. Finally, the regulation of genes encoding prenylcysteine metabolic enzymes in Arabidopsis will be examined. This work will significantly contribute to a better understanding of the metabolism of prenylated proteins and the role of prenylcysteine salvage/detoxification in plant growth and development. Broader Impacts The project will provide an excellent training environment for undergraduate and graduate students. IUPUI students will be recruited to work on this project from the Diversity Scholars Research Program, which is designed to encourage undergraduate women and minorities interested in graduate school to pursue undergraduate research opportunities, and the McNair Scholars Program, a federally funded program to increase the number of low-income, first-generation, underrepresented students in Ph.D. degree programs. Given the central location and urban environment of the IUPUI campus, it is expected that more young scientists, including women and minorities, will receive professional training through participation in this project.