Comparative analyses of immature and mature apple fruit peel proteomes

Abstract

The peel color of ‘Hongro’, an apple cultivar bred and cultivated in Korea, is greenish-yellow in the immature stage, turning to deep red in the mature stage. Conversely, the peel of ‘Greenball’ exhibits a greenish-yellow color in both its immature and mature stages. Following protein extraction from the peel of each apple cultivar and their separation via two-dimensional electrophoresis, 23 proteins in ‘Hongro’ and 9 proteins in ‘Greenball’ exhibited expression differences exceeding two-fold between the immature and mature stages. Proteins involved in carbohydrate metabolism, amino acid metabolism, plant hormone biosynthesis, lipid metabolism, transport, nucleotide metabolism, antioxidant enzymes, and allergens were expressed at higher levels in peels of mature ‘Hongro’ fruits compared to immature fruits. Conversely, proteins such as RuBisCO large subunit, RuBisCO activase, chloroplastic-like, oxygen-evolving enhancer protein 1, chloroplastic and PPD-containing proteins, involved in photosynthesis; and SAM synthase, involved in amino acid metabolism, were expressed at higher levels in the peels of immature ‘Hongro’ fruits, compared to mature fruits. In ‘Greenball’, proteins involved in amino acid metabolism, carbohydrate metabolism, nucleotide metabolism, and allergen expression were expressed at higher levels in mature ‘Greenball’ fruit peels compared to immature peels. In immature ‘Greenball’ peels, only the allergen agglutinin alpha chain-like was expressed at a higher level compared to mature ‘Greenball’ peels. The above results are expected to serve as foundational data for understanding the types and functions of proteins involved in the apple fruit ripening process and for improving target traits during the breeding of new apple varieties. © 2025 Korean Society for Plant Biotechnology.