|Hurkman Ii, William|
Submitted to: Journal of Proteomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2008
Publication Date: 4/13/2009
Citation: Montrichard, F., Alkhalfioui, F., Yano, H., Vensel, W.H., Hurkman II, W.J., Buchanan, B.B. 2009. Thioredoxin targets in plants: The first 30 years. Journal of Proteomics. 72(3):452-474. Interpretive Summary: Proteins constitute a large percentage of the plant cell and are fundamental to all biological processes. The functions of many proteins are facilitated by interactions with other proteins. Thioredoxin (Trx) is a small regulatory disulfide protein that influences virtually every major process of the cell, including carbon assimilation, seed germination, transcription, translation, cell division, redox signaling, radical scavenging and detoxification. The recent development of large scale methods for protein identification (proteomics) has led to the identification of approximately 500 proteins as potential or established Trx targets in land plants and oxygen-evolving microorganisms. These methods include protein labelling techniques and affinity chromatography methods that have enabled the detection and isolation of fractions enriched in putative Trx targets. In a widely used approach, proteins are separated by electrophoresis in one- or two-dimensional-gels (SDS-PAGE or 2DE) and identified by mass spectrometry. A recent application of a labelling technique based on the use of isotope-coded affinity tags (ICAT) not only can identify Trx targets, but can also determine their redox-active disulfides. This review provides an up-to-date, comprehensive list of established and potential target proteins currently known to be linked to Trx. More importantly, it presents an overview of the mechanisms involved in Trx regulation, approaches used to identify Trx targets, advantages and limits of proteomic approaches, and strategies for target validation. Knowledge of the regulation of cellular processes is essential for improving crop traits such as productivity, quality, and resistance to environmental conditions.
Technical Abstract: The turn of the century welcomed major developments in redox biology. In one development with plants, proteomics made possible the identification of proteins linked to thioredoxin (Trx), initially in chloroplasts and then other cell compartments. Two procedures, one based on thiol specific probes and the other on mutant Trx proteins, facilitated the labeling or isolation of potential Trx targets that were later identified with proteomic approaches. As a result, the number of targets in land plants increased 10-fold from fewer than 40 to more than 400. Additional targets have been identified in green algae and cyanobacteria, making a grand total of 500 in oxygenic photosynthetic organisms. Collectively these proteins have the potential to influence virtually every major process of the cell. A number of laboratories currently seek to confirm newly identified Trx targets by biochemical and genetic approaches. Almost certainly many new targets become redox active during oxidative stress, enabling the plant to cope with changing environments. Under these conditions, certain targets may be glutathionylated or nitrosylated such that reversion to the original reduced state is facilitated not only by Trx, but also, in some cases preferably, by glutaredoxin. When judging changes linked to Trx, it is prudent to recognize that effects transcend classical light/dark or oxidative regulation and fall in other arenas, in some cases yet to be defined. While future work will continue to give insight into functional details, it is clear that Trx plays a fundamental role in regulating diverse processes of the living cell.