|Hurkman Ii, William|
Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2004
Publication Date: 2/24/2004
Citation: Balmer, Y., Vensel, W.H., Tanaka, C.K., Hurkman, W.J., Gelhaye, E., Rouhier, N., Hacquot, J., Manieri, W., Schurmann, P., Buchanan, B.B. 2004. Thioredoxin links redox to the regulation of fundamental processes of plant mitochondria. Proceedings of the National Academy of Sciences. 2004. 101: 2642-2647 Interpretive Summary: Proteins constitute a large percentage of the plant cell and are fundamental to all cellular processes. Protein function is often facilitated through interactions with other proteins. Thioredoxin is a protein with a catalytically active disulfide group that is known to interact with many other proteins (target proteins) and, in this way, regulates a range of cellular activities. In previous studies, we identified target proteins in the cytoplasm or cellular matrix and in chloroplasts, specialized organelles for photosynthesis. In this study, we identified target proteins in mitochondria, specialized organelles for respiration. Mitochondria were isolated, proteins extracted, and over 50 target proteins identified. Based on their functions, thioredoxin regulates a number of processes in mitochondria, including photorespiration, protein assembly, hormone synthesis, and stress response. Knowledge of the coordinate regulation of cellular processes is essential to improving complex crop traits such as productivity and quality.
Technical Abstract: Mitochondria contain thioredoxin (Trx), a regulatory disulfide protein, and an associated flavoenzyme, NADP-thioredoxin reductase, that provide a link to NADPH in the organelle. Unlike animal and yeast counterparts, the function of Trx in plant mitochondria is largely unknown. Accordingly, we have applied recently devised proteomic approaches to identify soluble Trx-linked proteins in mitochondria isolated from photosynthetic (pea and spinach leaves) and heterotrophic (potato tubers) sources. Application of the mitochondrial extracts to mutant Trx affinity columns in conjunction with proteomics led to the identification of 52 potential Trx-linked proteins functional in 12 processes: photorespiration, citric acid cycle and associated reactions, lipid metabolism, electron transport, ATP synthesis/transformation, membrane transport, translation, protein assembly/folding, nitrogen metabolism, sulfur metabolism, hormone synthesis and stress-related reactions. Almost all of these targets were also identified by a fluorescent gel electrophoresis procedure in which reduction by Trx can be observed directly. In some cases, the processes targeted by Trx depended on the source of the mitochondria. The results support the view that Trx acts as a sensor and enables mitochondria to adjust key reactions in accord with prevailing redox state. These and earlier findings further suggest that, by sensing redox in chloroplasts and mitochondria, Trx enables the two organelles of photosynthetic tissues to communicate via a network of transportable metabolites such as dihydroxyacetone phosphate, malate and glycolate. In this way, light absorbed and processed via chlorophyll can be perceived and function in regulating fundamental mitochondrial processes akin to its mode of action in chloroplasts.