Flux balance analysis of metabolism during growth by osmotic cell expansion and its application to tomato fruits. (23rd March 2020) - Shameer, Sanu
Summary: Cell expansion is a significant contributor to organ growth and is driven by the accumulation of osmolytes to increase cell turgor pressure. Metabolic modelling has the potential to provide insights into the processes that underpin osmolyte synthesis and transport, but the main computational approach for predicting metabolic network fluxes, flux balance analysis, often uses biomass composition as the main output constraint and ignores potential changes in cell volume. Here we present growth‐by‐osmotic‐expansion flux balance analysis (GrOE‐FBA), a framework that accounts for both the metabolic and ionic contributions to the osmotica that drive cell expansion, as well as the synthesis of protein, cell wall and cell membrane components required for cell enlargement. Using GrOE‐FBA, the metabolic fluxes in dividing and expanding cells were analysed, and the energetic costs for metabolite biosynthesis and accumulation in the two scenarios were found to be surprisingly similar. The expansion phase of tomato fruit growth was also modelled using a multiphase single‐optimization GrOE‐FBA model and this approach gave accurate predictions of the major metabolite levels throughout fruit development, as well as revealing a role for transitory starch accumulation in ensuring optimal fruit development. Significance Statement: In flux balance analysis (FBA), a modelling approach widely used to study plant metabolism, growth is represented by the accumulation of biomass components in fixed proportions, which can be considered to be true during cell division. In plants, however, much of the observable growth results from cell expansion and so, in this paper, we introduce a framework for using FBA to study metabolism during cell expansion and demonstrate its application in predicting metabolic changes during tomato fruit development.