# Reduced MdFLS Expression Decreases Flavonol Content in Apple Flesh

## TL;DR

This study explores how apple genes affect flavonol levels in fruit flesh, which could improve the nutritional value of apples.

## Contribution

The study identifies functional flavonol synthase genes in apple and their role in flavonol accumulation in fruit flesh.

## Key findings

- MdFLS1, 2, and 3 are highly expressed in fruit skin but less so in flesh.
- Overexpression of MdFLS genes increases flavonol content in apple flesh.
- Light exposure boosts MdFLS1 and MdFLS2 expression and flavonol levels.

## Abstract

Flavonols contribute significantly to both plant defense and human health. In apple (Malus domestica), flavonols accumulate at high levels in leaves and fruit skin but are present at low levels in the fruit flesh, the primary tissue consumed by humans. Enhancing flavonol content in the flesh requires a deeper understanding of the underlying molecular mechanisms. In this study, we investigated the expression patterns and functional roles of four apple flavonol synthase genes (MdFLS1, 2, 3, 4). MdFLS1, 2, 3 exhibited higher expression in fruit skin than in flesh, while MdFLS4 was not expressed in either tissue. Transient overexpression of each gene promoted flavonol accumulation in apple fruit flesh, indicating that all four genes encode functional flavonol synthases. This enzyme activity was further confirmed through stable overexpression in transgenic Arabidopsis and tomato plants. Notably, light exposure of apple fruit flesh enhanced the expression of MdFLS1 and MdFLS2 and increased flavonol accumulation. These findings advance our understanding of flavonol biosynthesis in apple.