Spotlights on the post-translational regulation of enzymes involved in glucitol metabolism in peach (Prunus persica)

HARTMAN, MATÍAS D.; IGLESIAS, ALBERTO A.; ROJAS, BRUNO E.; FIGUEROA, CARLOS M.

Honolulu

Congreso; Plant Biology 2017; 2017

American Society of Plant Biologists

Inmost plants, fixed carbon is partitioned within cells between starch andsucrose. After its synthesis, sucrose is exported to sink tissues for carbonskeletons supply. Sugar alcohols (like glucitol -Gol-, mannitol or galactitol),along with sucrose and starch, are produced as primary photosynthates in asmall number of plant species. Gol is produced from glucose-6-phosphate by thecombined action of aldose-6-phosphate reductase (Ald6PRase) andGol-6-phosphatase. Gol is translocated into sink tissues where serves assubstrate of Gol dehydrogenase (GolDHase), oxidizing it to fructose. In thiswork we studied how post-translational modifications modulate the activity ofAld6PRase and GolDHase.Ald6PRasewas inhibited by sugar phosphates and inorganic phosphate, and its activity wasmodulated by compounds that react with Cys. Although Ald6PRasegluthationylation did not produce changes on enzymatic activity, it preventedthe enzyme from oxidative insolubility. Our results suggest that polyolsynthesis would maintain active under certain oxidative conditions, not onlybecause Ald6PRase is highly resistant to oxidants, but additionallyglutathionylation could have a protective role. Interestingly, polyols exert aprotective action against stress. Under severe stress conditions the Ald6PRasewould be inactivated.Wefound that oxidized gluthatione, hydrogen peroxide and diamide inactivatedGolDHase. Interestingly, reduced gluthatione and thioredoxin-h reverted theinactivation caused by oxidants, depending on initial inactivation degree. Dueto the high susceptibility of GolDHase to oxidants, we hypothesized that Golmetabolism in non-photosynthetic tissues would be rapidly down-regulated underoxidative stress conditions. Once redox imbalance is restored, GolDHase couldbe reactivated allowing normal carbon flux. Altogether,under stress conditions, Gol could exert protective functions not only in itssynthesis site (source leaves) but also at distant cells (sink tissues).Overall, both transcriptional and post-translational regulation of Gol enzymeswould operate in the same direction, to ensure an optimal defense barrieragainst stress.