Proteome Differences Expressed in the Peel of ‘Hongro’ and ‘Greenball’ Apples

Abstract

The peel colors of ‘Hongro’ and ‘Greenball’, apple cultivars bred and cultivated in Korea, were deep red and greenish yellow, respectively, at the time of harvest. ‘Hongro’ had more peel redness than ‘Greenball’, while ‘Greenball’ had more peel yellowness (b value) than ‘Hongro’. As a result of separating proteins extracted from the peels of the two apple cultivars by means of two-dimensional electrophoresis (2-DE), 17 protein spots in ‘Hongro’ and 12 in ‘Greenball’ exhibited expression rates more than twice those in the other cultivar. Through a matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass (MALDI-TOF/TOF) analysis, ten spots in ‘Hongro’ and five spots in ‘Greenball’ were identified as proteins with specific physiological functions. In’ Hongro’, the following proteins were expressed at higher levels than in ‘Greenball’: NADP-dependent malic enzyme (spot 1), enolase-like (spot 2), formate dehydrogenase, mitochondrial (spots 3 and 9) and glyoxalase Ⅰ (spot 13) involved in carbohydrate metabolism; 12-oxophytodienoate reductase 2-like (spot 6) catalyzing the biosynthesis of JA, a type of plant hormone; β-(cyanoalanine synthase) CAS 1 (spot 8) involved in amino acid metabolism; L-ascorbate peroxidase (AP) 2, cytosolic (spot 17) and glutathione S-transferase (GST)-like (spot 19), a type of antioxidant enzyme; and agglutinin alpha chain-like (spot 21), an allergen. In ‘Greenball’, the following proteins were expressed at higher levels than in ‘Hongro’: DJ-1 homolog D-like (spot 4) and thiamine thiazole synthase, chloroplastic (spot 11), which are involved in carbohydrate metabolism; ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) activase, chloroplastic-like (spot 5), oxygen-evolving enhancer protein 1, chloroplastic (spot 16), and PsbP domain (PPD)-containing protein (spot 18), all of which are involved in photosynthesis. Meanwhile, among the proteins whose expression rates differed between ‘Hongro and ‘Greenball’, no proteins directly related to the development of peel color were identified. Additionally, seven proteins in ‘Hongro’ and seven in ‘Greenball’ were identified as unidentified or uncharacterized proteins. These results can be used for a wide range of studies related to the sensory quality, characteristics, production, and preservation of apples and can also serve as basic data for improving target traits in the breeding of new varieties.