Transcriptomic and Metabolic Profiles of Apple Peels of Different Colors

TL;DR

This study explores the genetic and metabolic factors behind yellow apple peel coloration, identifying LAR1 and specific metabolites like catechin and epicatechin as key contributors.

Contribution

The study provides the first integrated transcriptomic and metabolomic evidence for yellow apple peel coloration, highlighting LAR1 and flavonoid metabolites.

Findings

LAR1 gene is critical for yellow apple peel coloration in 'Venus Gold' apples.

Catechin and epicatechin levels are higher in yellow peels compared to red ones.

Hundreds of volatile metabolites differ significantly among apple peels of different colors.

Abstract

Apple (Malus domestica) is a woody fruit tree belonging to the Rosaceae family, genus Malus. It has been widely reported that MYB transcription factors are critical regulators for the red color of apple peel by activating the expression of anthocyanin biogenesis genes. However, it is still not clear what the molecular mechanism for the yellow color of apple peel is. In order to investigate key genes and metabolites responsible for yellow coloration of apple peel, three strains of apples, “Venus Gold (Ype)” with yellow peel, “Yanfu8 (Mpe)” with medium red peel, and “Red love” with dark red peel, were selected in this study. Transcriptomic and metabolomic profiles were obtained for the peels of the three apple strains. After analyzing the transcriptomic profiles and being verified with qRT-PCR experiments, our results suggest that LAR1 is a critical gene for the yellow color of Ype peel. Analysis of metabolomic profiles revealed that the abundances of catechin and epicatechin in Ype peel were higher than those in Rpe, indicating an important reason for the yellow color of Ype peel. Furthermore, when comparing volatile metabolites from Ype, Mpe, and Rpe, hundreds of volatile metabolites show significantly different abundances, suggesting that apples with different peel colors have different odors. Our results uncover a novel metabolic mechanism for yellow coloration, where high expression of LAR1 promotes accumulation of catechin and epicatechin, providing the first integrated transcriptomic and metabolomic evidence for this pathway in apple peel.

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