Effect of Reflected Sunlight on Differential Expression of Anthocyanin Synthesis-Related Genes in Young Apple Fruit

Abstract

ABSTRACT Anthocyanin accumulation is responsible for the red color of the skin of apple fruits (Malus × domestica Borkh.). Environmental stimuli, such as light, temperature, soil factors, tree factors, and the application of chemicals can alter the synthesis of anthocyanins. Herein, we examined the expression of genes related to anthocyanin biosynthesis in the fruit of apple cultivars, ‘Summer Prince’ and ‘Arisoo’ at the early stage of fruit development 60 DAFB (days after full bloom). The expression of genes, which included structural and regulatory genes involved in anthocyanin biosynthesis, and light-responsive genes was determined in fruits developed under the effect of sunlight exposure for seven days. Apple fruits were divided in to: ‘reflected sunlight’, ‘bagged’, and ‘control’ groups. The expression levels of the anthocyanin synthesis-related genes were significantly different among the groups and between the shaded and reflected sides. We also determined the difference in coloration patterns in the different groups using the colorimetric coordinates method. The shaded side of apple fruits quickly turned more redder after exposure to reflected sunlight and the coloration was almost similar to that on the exposed side after the treatment. Strong correlation coefficients between anthocyanin-related gene expression levels and coloration patterns were obtained. This study shows that sunlight plays an important role in stimulating the coloration of apple fruit by regulating the expression of genes involved in anthocyanin accumulation during the early stage of fruit development. The present study assumes importance because redder fruits, generated through a non-transgenic approach would be more acceptable to consumers.