Biography
A native Virginian, Bob B. Buchanan received his doctorate in microbiology from Duke University. Following postdoctoral study, he accepted a faculty appointment at the University of California Berkeley where he has spent his entire career. Early on, he and his collaborators demonstrated the reversibility of the citric acid cycle and its use as a path of carbon dioxide fixation in photosynthetic bacteria. An extension of the bacterial work led to the discovery of the role of the protein, thioredoxin, in linking light to the regulation of enzymes of oxygenic photosynthesis. While uncovered in studies with chloroplasts, this type of regulation, now known as redox regulation, has been found to occur in all types of cells. More recently, he and his collaborators have demonstrated a role for thioredoxin in a number of other processes, including seed germination. They have also identified potential applications of thioredoxin. Buchanan is a member of the National Academy of Sciences.
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The Horizon of Redox Regulation Continues
to Broaden in Plants
Abstract:
Thioredoxins (Trxs) are small proteins that occur in all types of organisms. Nineteen different Trx isoforms grouped in 6 subfamilies and distributed throughout the cell have been identified in the Arabidopsis thaliana genome. Trxs contain a conserved redox active disulfide, WC[G/P]PC, that is reduced either (1) photosynthetically by ferredoxin via ferredoxin-thioredoxin reductase in chloroplasts, or (2) enzymatically by NADPH via NADP-thioredoxin reductase in other organelles. Reduced Trxs function as hydrogen donors for the reduction of substrates, such as ribonucleotides, or, more broadly, in the regulation of enzymes (redox regulation). For the first 25 years following its identification in chloroplasts, Trxs were linked to the regulation of a limited number of proteins. The advent of proteomics has made possible the identification of more than 250 Trx-linked proteins, most previously unrecognized, and suggested a role for Trx in new types of regulation and in modes of communication between organs and organelles. In seeds, the role of Trx has been extended to amyloplasts—the site of starch synthesis and storage. Amyloplasts were found to have a complete ferredoxin-linked system that, like the chloroplast counterpart, targets a spectrum of proteins. Recent work on Trx has also uncovered previously unknown roles for redox regulation in chloroplasts—e.g., in linking protein phosphorylation to starch metabolism in the stroma and in regulating enzyme activity in the thylkoid lumen. Redox has also assumed a prominent role in processes important to agriculture such as response to drought. Current evidence indicates that redox regulates processes functional at virtually every stage of plant development and, in addition, participates in a growing number of stress responses.
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