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Stressed Soybean Signaling

Glutathione protects legumes from oxidative damage that arises from various stress conditions. Considerable increases in the pool size of glutathione have been reported in plants exposed to various abiotic and biotic stresses. Increased glutathione concentrations have also been observed when cysteine content is increased artificially, suggesting that cysteine availability plays an important role in determining glutathione content.

Phosphorylation of GmSerat2;1 by CDPK increases glutathione production, which results in the stress response.

In this Paper of the Week, Fenglong Liu and colleagues show that phosphorylation of a soybean serine acetyltransferase by a calcium-dependent protein kinase (CDPK) is involved in regulating cysteine synthesis and thus the oxidative stress response. The soybean serine acetyltransferase GmSerat2;1 catalyzes the first reaction in the biosynthesis of cysteine from serine. Liu et al. showed that phosphorylation of GmSerat2;1 at a specific serine residue in the carboxyl terminus renders the enzyme insensitive to feedback inhibition by cysteine. Furthermore, treatment of cells with hydrogen peroxide induced both phosphorylation and protein synthesis of GmSerat2;1. Based on these results the authors propose that a hydrogen peroxide-induced increase in GmSerat2;1 activity contributes to the oxidative stress response in soybean. Since the targets of protein kinases are still very poorly defined in most plant systems, the results described here are important for understanding the signaling mechanisms mediated through plant CDPKs.

FOOTNOTES

See referenced article, J. Biol. Chem. 2006, 281, 27405-27415

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