Identification and functional characterization of sorbitol-6-phosphate dehydrogenase protein from rice and structural elucidation by in silico approach

Two G-box-like elements essential to high gene expression of SlAKR4B in tomato leaves

Aldo-keto reductases (AKRs) play important roles in aldehyde detoxification as well as primary and secondary metabolism in plants. We previously reported inducible expression of a Solanum lycopersicum AKR4B (SlAKR4B) in tomato leaves treated with salicylic acid and jasmonic acid, and high promoter activity of SlAKR4B in tomato leaf protoplasts. In this study, we investigated the expression response of SlAKR4B in the tomato leaves with infiltration treatment and the cis-element(s) involved in high promoter activity. Gene expression analysis in tomato leaf protoplasts and buffer-infiltrated tomato leaves suggested that cell damage caused the increased expression of SlAKR4B. Promoter activity of SlAKR4B was significantly reduced by mutation of two G-box like elements. It is suggested that the two G-box like elements are responsible for the high promoter activity.

Chromatin-associated regulation of sorbitol synthesis in flower buds of peach

PpeS6PDH gene is postulated to mediate sorbitol synthesis in flower buds of peach concomitantly with specific chromatin modifications. Perennial plants have evolved an adaptive mechanism involving protection of meristems within specialized structures named buds in order to survive low temperatures and water deprivation during winter. A seasonal period of dormancy further improves tolerance of buds to environmental stresses through specific mechanisms poorly known at the molecular level. We have shown that peach PpeS6PDH gene is down-regulated in flower buds after dormancy release, concomitantly with changes in the methylation level at specific lysine residues of histone H3 (H3K27 and H3K4) in the chromatin around the translation start site of the gene. PpeS6PDH encodes a NADPH-dependent sorbitol-6-phosphate dehydrogenase, the key enzyme for biosynthesis of sorbitol. Consistently, sorbitol accumulates in dormant buds showing higher PpeS6PDH expression. Moreover, PpeS6PDH gene expression is affected by cold and water deficit stress. Particularly, its expression is up-regulated by low temperature in buds and leaves, whereas desiccation treatment induces PpeS6PDH in buds and represses the gene in leaves. These data reveal the concurrent participation of chromatin modification mechanisms, transcriptional regulation of PpeS6PDH and sorbitol accumulation in flower buds of peach. In addition to its role as a major translocatable photosynthate in Rosaceae species, sorbitol is a widespread compatible solute and cryoprotectant, which suggests its participation in tolerance to environmental stresses in flower buds of peach.

Inhibition of Recombinant Aldose-6-Phosphate Reductase from Peach Leaves by Hexose-Phosphates, Inorganic Phosphate and Oxidants

Glucitol, also known as sorbitol, is a major photosynthetic product in plants from the Rosaceae family. This sugar alcohol is synthesized from glucose-6-phosphate by the combined activities of aldose-6-phosphate reductase (Ald6PRase) and glucitol-6-phosphatase. In this work we show the purification and characterization of recombinant Ald6PRase from peach leaves. The recombinant enzyme was inhibited by glucose-1-phosphate, fructose-6-phosphate, fructose-1,6-bisphosphate and orthophosphate. Oxidizing agents irreversibly inhibited the enzyme and produced protein precipitation. Enzyme thiolation with oxidized glutathione protected the enzyme from insolubilization caused by diamide, while incubation with NADP+ (one of the substrates) completely prevented enzyme precipitation. Our results suggest that Ald6PRase is finely regulated to control carbon partitioning in peach leaves.