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Abstract

Fruit quality, defined by traits such as fruit size and composition, is a multi-criteria concept  and the result of a complex network of interacting biological processes, under the effect of environment. Aim of the Virtual fruit model is to connect existing models describing fruit growth and respiration, sugar and acid accumulation, ethylene production and use them to in silico analyze the impact of mutations, or naturally occurring genetic variations, under different environmental scenarii.
 In its original version, the Virtual fruit model makes uses of coarse-grained, empirical description of physiological processes. Moreover, the fruit is described as single big compartment, in expansion, without considering the specificities of the early developmental phase, namely the coexistence of cell division and expansion processes. Current advances in molecular and developmental biology claim for an improved description of the biological mechanisms, taking advantage of available omics data.
 In this perspective, a kinetic model of sugar metabolism has been recently developed to simulate the concentrations of sugars (sucrose, glucose, fructose and sorbitol) during fruit development in peach, taking advantage of recent profiling data. Cellular compartmentation (cytosol and vacuole) is explicitly described and data-driven enzyme capacities are used to parameterize the equations. The model correctly accounts for both genetic and annual variability observed in experimental data of ten genotypes and provides clues into the molecular mechanisms involved in the specification of phenotypic differences.
 
 In parallel, an integrated model of tomato growth, explicitly accounting for cell proliferation and expansion processes, has been developed and used to investigate the impact of water deficit and carbon limitation on the resulting fruit growth. Results show the effect of stress on individual cells strongly depends on their age, size and uptake capabilities and that the timing of stress application, together with the fruit position on the plant, is crucial to determine the final phenotypic outcome. In the future, the addition of DNA endoreduplication to the model and the description of the cell cycle adjustments to environmental conditions will help to refine model predictions, shedding light on the complex control of growth plasticity.