Regulation of Glucitol Dehydrogenase from Peach Fruits by Post-translational Modifications

C.M. FIGUEROA; M.D. HARTMAN; A.A. IGLESIAS

Minneapolis

Congreso; Annual Meeting of the American Society of Plant Biologists of Plant Physiologists; 2011

American Society of Plant Biologists

Sucrose and starch are major photosynthetic products in plants. Interestingly, a thirdcompound is produced in species from the Rosaceae family. Glucitol (Gol) is synthesized inmature leaves and used for carbon translocation to heterotrophic tissues, where it isconverted 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 isknown about its regulation. Herein, we report the heterologous expression and kineticcharacterization of GolDHase from peach (Prunus persica) fruits (PpeGolDHase). We foundthat 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 wasincubated with oxidizing reagents like diamide, H2O2 and oxidized glutathione (k´´ valueswere 12.3, 6.93 and 0.086 M-1s-1, respectively). The activity of the oxidized enzyme wasrecovered by reduction with DTT, reduced glutathione and recombinant thioredoxins fromEscherichia coli and wheat leaves. Considering that Gol accumulation has been related withabiotic 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 ahydroxyl-radical scavenger. We also found that PpeGolDHase can be in vitro phosphorylated by a Mg2+- and Ca2+-dependent protein kinase present in protein extractsfrom peach fruits. In silico analysis, including molecular modeling, allowed us to identify aputative 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 posttranslational in vivo regulation.