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标题：NTRC links built-in thioredoxin to light and sucrose in regulating starch synthesis in chloroplasts and amyloplasts
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作者：Justyna Michalska ; Henrik Zauber ; Bob B. Buchanan 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2009
卷号：106
期号：24
页码：9908-9913
DOI：10.1073/pnas.0903559106
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Plants have an unusual plastid-localized NADP-thioredoxin reductase C (NTRC) containing both an NADP-thioredoxin reductase (NTR) and a thioredoxin (Trx) domain in a single polypeptide. Although NTRC is known to supply reductant for detoxifying hydrogen peroxide in the dark, its other functions are unknown. We now report that NTRC plays a previously unrecognized role in the redox regulation of ADP-glucose pyrophosphorylase (AGPase), a central enzyme of starch synthesis. When supplied NADPH, NTRC activated AGPase in vitro in a redox reaction that required the active site cysteines of both domains of the enzyme. In leaves, AGPase was activated in planta either by light or external feeding of sucrose in the dark. Leaves of an Arabidopsis NTRC KO mutant showed a decrease both in the extent of redox activation of AGPase and in the enhancement of starch synthesis either in the light (by 40-60%) or in the dark after treatment with external sucrose (by almost 100%). The light-dependent activation of AGPase in isolated chloroplasts, by contrast, was unaffected. In nonphotosynthetic tissue (roots), KO of NTRC decreased redox activation of AGPase and starch synthesis in response to light or external sucrose by almost 90%. The results provide biochemical and genetic evidence for a role of NTRC in regulating starch synthesis in response to either light or sucrose. The data also suggest that the Trx domain of NTRC and, to a lesser extent, free Trxs linked to ferredoxin enable amyloplasts of distant sink tissues to sense light used in photosynthesis by leaf chloroplasts and adjust heterotrophic starch synthesis accordingly.
关键词：NADP-thioredoxin reductase ; sugar sensing ; redox regulation ; ADP-glucose pyrophosphorylase