Regulation of glucitol dehydrogenase from peach fruits by post-translational modifications

FIGUEROA CM; HARTMAN MD; IGLESIAS AA

Minneapolis

Congreso; Plant Biology 2011; 2011

American Society of Plant Biologists

Sucrose and starch are major photosynthetic products in plants. Interestingly, a third compound is produced in species from the Rosaceae family. Glucitol (Gol) is synthesized in mature leaves and used for carbon translocation to heterotrophic tissues, where it is converted into fructose by a NAD-dependent Gol dehydrogenase (GolDHase, EC 1.1.1.14). Despite the importance of this enzyme for carbon partitioning in these plants, little is known about its regulation. Herein, we report the heterologous expression and kinetic characterization of GolDHase from peach (Prunus persica) fruits (PpeGolDHase). We found that the recombinant enzyme was highly inhibited by Cu2+ and Hg2+, with I0.5 of 31 and 96 nM, respectively. In addition, loss of activity was observed when PpeGolDHase was incubated with oxidizing reagents like diamide, H2O2 and oxidized glutathione (k´´ values were 12.3, 6.93 and 0.086 M-1s-1, respectively). The activity of the oxidized enzyme was recovered by reduction with DTT, reduced glutathione and recombinant thioredoxins from Escherichia coli and wheat leaves. Considering that Gol accumulation has been related with abiotic stress tolerance, we hypothesize that PpeGolDHase could be inhibited under oxidative stress, thus maintaining levels of Gol high enough to exert a protective role as a hydroxyl-radical scavenger. We also found that PpeGolDHase can be in vitro phosphorylated by a Mg2+- and Ca2+-dependent protein kinase present in protein extracts from peach fruits. In silico analysis, including molecular modeling, allowed us to identify a putative site for phosphorylation in PpeGolDHase. As a whole, results support that in peach (and probably also in other Rosaceae plants) GolDHase could be a key target for post-translational in vivo regulation.