Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
Japan Society for Promotion of Science, Kojimachi, Tokyo 102-0083, Japan.
Proc Natl Acad Sci U S A. 2020 Sep 22;117(38):23970-23981. doi: 10.1073/pnas.2011859117. Epub 2020 Sep 3.
Fruit set is the process whereby ovaries develop into fruits after pollination and fertilization. The process is induced by the phytohormone gibberellin (GA) in tomatoes, as determined by the constitutive GA response mutant However, the role of GA on the metabolic behavior in fruit-setting ovaries remains largely unknown. This study explored the biochemical mechanisms of fruit set using a network analysis of integrated transcriptome, proteome, metabolome, and enzyme activity data. Our results revealed that fruit set involves the activation of central carbon metabolism, with increased hexoses, hexose phosphates, and downstream metabolites, including intermediates and derivatives of glycolysis, the tricarboxylic acid cycle, and associated organic and amino acids. The network analysis also identified the transcriptional hub gene , that coordinated metabolic activation. Furthermore, a kinetic model of sucrose metabolism predicted that the sucrose cycle had high activity levels in unpollinated ovaries, whereas it was shut down when sugars rapidly accumulated in vacuoles in fruit-setting ovaries, in a time-dependent manner via tonoplastic sugar carriers. Moreover, fruit set at least partly required the activity of fructokinase, which may pull fructose out of the vacuole, and this could feed the downstream pathways. Collectively, our results indicate that GA cascades enhance sink capacities, by up-regulating central metabolic enzyme capacities at both transcriptional and posttranscriptional levels. This leads to increased sucrose uptake and carbon fluxes for the production of the constituents of biomass and energy that are essential for rapid ovary growth during the initiation of fruit set.
坐果是授粉和受精后子房发育成果实的过程。在番茄中，这一过程是由植物激素赤霉素（GA）诱导的，这一点已被组成型 GA 反应突变体所确定。然而，GA 对坐果子房代谢行为的影响在很大程度上仍然未知。本研究通过整合转录组、蛋白质组、代谢组和酶活性数据的网络分析，探讨了坐果的生化机制。我们的研究结果表明，坐果涉及到中心碳代谢的激活，伴随着己糖、己糖磷酸和下游代谢物的增加，包括糖酵解、三羧酸循环及其相关有机和氨基酸的中间产物和衍生物。网络分析还确定了转录枢纽基因 ，它协调了代谢的激活。此外，蔗糖代谢的动力学模型预测，在未授粉的子房中有很高的蔗糖循环活性水平，而在坐果的子房中，糖迅速积累在液泡中时，蔗糖循环活性水平会被液泡膜上的糖载体以时间依赖性的方式关闭。此外，坐果至少部分需要果糖激酶的活性，果糖激酶可能将果糖从液泡中抽出，从而为下游途径提供物质。总之，我们的研究结果表明，GA 级联通过在上转录和转录后水平上调中心代谢酶的能力来增强汇的能力。这导致蔗糖摄取和碳通量的增加，用于产生生物量和能量的组成部分，这对于在果实起始时迅速生长的子房生长是必不可少的。
