A proteometabolomic study of Actinidia deliciosa fruit development

Green-fleshed kiwifruit is worldwide appreciated for its flavor and macronutrients that are related to its physiological development. Fruit ripe stage for harvesting does not correspond to an optimal edible condition due to firmness/acidity pome characteristics; this is overcome with postharvest fruit processing. To describe the metabolic pathways/molecular effectors underlying Actinidia deliciosa cv. Hayward pome physiological development, kiwifruits were harvested at four growth stages (from fruit set to physiological maturity), and corresponding outer endocarp samples were analysed for metabolite and protein content. Combined NMR/LC-UV/ ESI-IT-MSn procedures quantified 46 metabolites at these developmental stages; similarly, integrated 2D-DIGE/ nLC-ESI-LIT-MS/MS analyses described corresponding proteomic changes. Quantitative protein dynamics showed that components related to disease/defense, protein destination/storage, metabolism, energy and cell structure functions were highly affected at specific moments of fruit development, suggesting a rationale to pomological and metabolite content characteristics at those times. Bioinformatic interaction prediction revealed a main network of differentially represented proteins, which may control metabolic changes in developing kiwifruit. Main pome allergens were also quantified, demonstrating their highest levels at the mature stage. By aligning kiwifruit development to a proteometabolomic representation, this investigation integrates previous metabolic observations and provides a reference framework for further physiological/nutritional studies, also allowing cross comparison among crop species. Biological significance: Compared with some other fruits, green-fleshed kiwifruit is unique for its nutrient density, health benefits, and consumer appeal; in fact, it is exceptionally rich in vitamins, carotenoids, potassium, fibre and phytochemicals acting in synergy to achieve multiple health advantages. However, kiwifruit is allergenic, and although symptoms in most susceptible individuals are mild, severe reactions have also been described. In the course of their 6-month development, kiwifruit undergoes radical changes in its morphology and chemical composition; these modifications may highly affect fruit nutraceutical and allergenic properties. To gain a better understanding of the molecular processes regulating metabolite concentration during fruit development but also affecting general pomological characteristics, a time-course metabolomic and proteomic analysis of kiwifruit flesh tissues was undertaken. Combined information on modified levels of 46 metabolites and 241 proteins showed that molecular processes underlying central and secondary metabolism, energy, cell structure, protein destination/storage, disease/defense kiwifruit functions were highly affected during fruit development, providing a rationale to the corresponding changes in organic acids, sugars, amino acids, polyphenols, fatty acids, phospholipids and allergens content, but also to the corresponding modifications in pome firmness, pulp colour