Zakhartsev Maksim, Medvedeva Irina, Orlov Yury, Akberdin Ilya, Krebs Olga, Schulze Waltraud X
Department of Plant Systems Biology, University of Hohenheim, Fruwirthstraße 12, 70599, Stuttgart, Germany.
Novosibirsk State University, Pirogova 2, 630090, Novosibirsk, Russia.
BMC Plant Biol. 2016 Dec 28;16(1):262. doi: 10.1186/s12870-016-0868-3.
Sucrose translocation between plant tissues is crucial for growth, development and reproduction of plants. Systemic analysis of these metabolic and underlying regulatory processes allow a detailed understanding of carbon distribution within the plant and the formation of associated phenotypic traits. Sucrose translocation from 'source' tissues (e.g. mesophyll) to 'sink' tissues (e.g. root) is tightly bound to the proton gradient across the membranes. The plant sucrose transporters are grouped into efflux exporters (SWEET family) and proton-symport importers (SUC, STP families). To better understand regulation of sucrose export from source tissues and sucrose import into sink tissues, there is a need for a metabolic model that takes in account the tissue organisation of Arabidopsis thaliana with corresponding metabolic specificities of respective tissues in terms of sucrose and proton production/utilization. An ability of the model to operate under different light modes ('light' and 'dark') and correspondingly in different energy producing modes is particularly important in understanding regulatory modules.
Here, we describe a multi-compartmental model consisting of a mesophyll cell with plastid and mitochondrion, a phloem cell, as well as a root cell with mitochondrion. In this model, the phloem was considered as a non-growing transport compartment, the mesophyll compartment was considered as both autotrophic (growing on CO under light) and heterotrophic (growing on starch in darkness), and the root was always considered as heterotrophic tissue dependent on sucrose supply from the mesophyll compartment. In total, the model includes 413 balanced compounds interconnected by 400 transformers. The structured metabolic model accounts for central carbon metabolism, photosynthesis, photorespiration, carbohydrate metabolism, energy and redox metabolisms, proton metabolism, biomass growth, nutrients uptake, proton gradient generation and sucrose translocation between tissues. Biochemical processes in the model were associated with gene-products (742 ORFs). Flux Balance Analysis (FBA) of the model resulted in balanced carbon, nitrogen, proton, energy and redox states under both light and dark conditions. The main H-fluxes were reconstructed and their directions matched with proton-dependent sucrose translocation from 'source' to 'sink' under any light condition.
The model quantified the translocation of sucrose between plant tissues in association with an integral balance of protons, which in turn is defined by operational modes of the energy metabolism.
植物组织间的蔗糖转运对于植物的生长、发育和繁殖至关重要。对这些代谢及潜在调控过程进行系统分析，有助于详细了解植物体内的碳分配以及相关表型性状的形成。蔗糖从“源”组织（如叶肉）向“库”组织（如根）的转运与跨膜质子梯度紧密相关。植物蔗糖转运蛋白可分为外排转运体（SWEET家族）和质子同向转运体（SUC、STP家族）。为了更好地理解源组织中蔗糖的输出调控以及库组织中蔗糖的输入调控，需要一个代谢模型，该模型要考虑拟南芥的组织结构以及各组织在蔗糖和质子产生/利用方面相应的代谢特异性。该模型在不同光照模式（“光”和“暗”）下以及相应的不同能量产生模式下运行的能力，对于理解调控模块尤为重要。
在此，我们描述了一个多隔室模型，该模型由一个带有质体和线粒体的叶肉细胞、一个韧皮部细胞以及一个带有线粒体的根细胞组成。在这个模型中，韧皮部被视为一个非生长的运输隔室，叶肉隔室被视为既能自养（在光照下以二氧化碳为原料生长）又能异养（在黑暗中以淀粉为原料生长），而根始终被视为依赖叶肉隔室提供蔗糖的异养组织。该模型总共包括413种平衡化合物，由400个转化器相互连接。这个结构化的代谢模型涵盖了中心碳代谢、光合作用、光呼吸、碳水化合物代谢、能量和氧化还原代谢、质子代谢、生物量生长、养分吸收、质子梯度产生以及组织间的蔗糖转运。模型中的生化过程与基因产物（742个开放阅读框）相关联。对该模型进行通量平衡分析（FBA），结果显示在光照和黑暗条件下碳、氮、质子、能量和氧化还原状态均达到平衡。主要的H通量得以重建，并且它们的方向与在任何光照条件下质子依赖的蔗糖从“源”到“库”的转运相匹配。
该模型量化了植物组织间蔗糖的转运，并与质子的整体平衡相关联，而质子平衡又由能量代谢模式所定义。
