Comparative Analysis of the Proteome in the Peel and Flesh of 'Hongro' Apples

The proteome expressed in the peel and flesh of 'Hongro', a domestic breeding apple cultivar, was extracted and separated by two-dimensional electrophoresis. Most of the proteins were expressed at similar levels in the peel and flesh, but 30 protein spots showed a difference of more than two times higher in expression level in the peel and flesh. Of these, 25 were higher in the peel and 5 were higher in the flesh. By analyzing these proteins with MALDI-TOF/TOF, 18 of the protein spots that were higher in the peel were identified as proteins with their respective functions, and the remaining 7 were identified as having unknown function or were unidentified. In the case of the protein spots expressed higher in the flesh, two were identified as proteins having respective functions, and the other three were unidentified. Proteins more highly expressed in the peel were 1-aminocyclopropane-1-carboxylate oxidase homolog (spot 21) related to the biosynthesis of ethylene; acetyl-CoA acetyltransferase (spot 148), cytosolic 1, acetyl-CoA acetyltransferase, cytosolic 1-like (spot 316) and 8-hydroxygeraniol dehydrogenase-like (spot 348) related to the biosynthesis of secondary metabolites; oxygen-evolving enhancer protein 1, chloroplastic (spot 210), and ribulose-1, 5-bisphosphate carboxylase/oxygenase large subunit (spot 273) related to the photosynthesis; (+)-neomenthol dehydrogenase-like (spot 216 and 219), formate dehydrogenase, mitochondrial (spot 305), glutathione S-transferase-like (spot 483 and 484), and acidic endochitinase SE 2-like, partial (spot 391 and 392) related to the biological defense and stress response; and antioxidant enzyme L-ascorbate peroxidase 2 (spot 221), MLP-like protein 34 (spot 406), major allergen Mal d 1 (spot 451 and 452), and major allergen Mal d 1.06A01 (spot 457) related to allergies. On the other hand, proteins that were more highly expressed in the flesh were chaperonin 60 subunit alpha 1, chloroplastic (spot 8) related to protein folding, and NADP-dependent D-sorbitol-6-phosphate dehydrogenase (spot 380) related to carbohydrate metabolism. These results will be useful in a wide range of studies related to apple breeding, storage, quality, and environmental tolerance.