Effect of the overexpression of the GGP1 gene on cell wall remodelling and redox state in the tomato fruit.

Tomato fruit ripening is a complex physiological process that involves morphological, anatomical, biochemical, and molecular alterations. One of these changes occurring during ripening is the softening of the fruit, which is attributed to modifications in the biosynthesis and degradation of individual cell wall components, i.e. polysaccharides and proteoglycans. In addition, ripening is affected by redox processes, and interplay of the reactive oxygen species (ROS) and specific antioxidants, enzymes, ascorbate, and phenolic compounds. The present study aims to determine the impact of the overexpression of the GDP-l-galactose phosphorylase (GGP1) gene under the control of two fruit-specific promoters, namely PPC - phosphoenolpyruvate carboxylase and PG - polygalacturonase on cell wall properties, activities of H2O2-regulating enzymes and the abundance of phenolic compounds. PPC-GGP1 and PG-GGP1 transgenic lines revealed significant structural changes in fruit parenchyma, compared to wild type fruit, followed by a disturbance in the spatial distribution and molecular & chemical composition of homogalacturonans. In addition, cell wall-bound monolignol, p-coumaryl alcohol was higher in transgenic fruit compared with wild type ones. Lastly, the catalase and ascorbate peroxidase activities were lower in PPC-GGP1 fruits, indicating changes in the regulation of antioxidative defense during the ripening process of this line. These results suggest that overexpression of the GGP1 gene affects the cell wall remodelling and redox state in the red ripe tomato fruits.