Department of Plant Sciences, University of Oxford, Oxford, UK.
Max Planck Institute for Molecular Plant Physiology, Potsdam-Golm, Germany.
Plant J. 2020 Jul;103(1):68-82. doi: 10.1111/tpj.14707. Epub 2020 Mar 23.
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.
细胞扩张是器官生长的重要贡献者，是由渗透物的积累来增加细胞膨压驱动的。代谢建模有可能深入了解支持渗透物合成和运输的过程，但预测代谢网络通量的主要计算方法——通量平衡分析（FBA），通常使用生物质组成作为主要输出约束，而忽略了细胞体积的潜在变化。在这里，我们提出了一种基于渗透压膨胀的生长通量平衡分析（GrOE-FBA）框架，该框架考虑了驱动细胞扩张的代谢和离子对渗透压的贡献，以及为细胞增大所需的蛋白质、细胞壁和细胞膜成分的合成。使用 GrOE-FBA 分析了分裂和扩张细胞的代谢通量，发现两种情况下代谢物生物合成和积累的能量成本惊人地相似。还使用多相单优化 GrOE-FBA 模型对番茄果实生长的扩张阶段进行了建模，该方法准确预测了整个果实发育过程中的主要代谢物水平，同时还揭示了暂态淀粉积累在确保最佳果实发育中的作用。
