Rapid transporter regulation prevents substrate flow traffic jams in boron transport.
Rapid transporter regulation prevents substrate flow traffic jams in boron transport.
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DOI：
10.7554/elife.27038
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发表时间：
2017-09-05
期刊：
影响因子：
7.7
通讯作者：
Grieneisen VA
中科院分区：
文献类型：
--
作者：
Sotta N;Duncan S;Tanaka M;Sato T;Marée AF;Fujiwara T;Grieneisen VA
根部对养分的吸收通常涉及底物依赖性调节养分转运蛋白。为了实现强劲的吸收，该系统需要细胞内的调节回路以及整个组织的集体协调行为。这种系统的一个范例是硼吸收，以其定向运输和稳态而闻名，因为硼对于植物生长至关重要，但在高浓度下有毒。在拟南芥中，硼的吸收是通过扩散促进剂（NIP）和输出剂（BOR）发生的，每种都呈现出不同的极性。有趣的是，尽管土壤中硼浓度均匀且稳定，但这两种转运蛋白都表现出惊人的快速硼依赖性调节。通过数学模型，我们证明这些转运蛋白的较慢调节会导致生理上有害的振荡行为。细胞定期暴露于具有潜在细胞毒性的硼水平，并且木质部的养分输送量受到阻碍。我们的结论是，在维持稳态的同时，极化组织环境中的快速转运蛋白调节对于防止营养物流的内在交通拥堵行为至关重要。每个多细胞生物体，包括所有植物和动物，都面临着吸收所需营养并将其分布到全身的挑战。植物从土壤中吸收许多营养物质，包括氮和硼，进入根部，通常使用严格控制的过程，需要能量才能发挥作用。植物根部包含几个不同的细胞层，养分需要穿过这些层才能到达根部中心的通道（称为木质部），该通道将养分输送到植物的其他部分。植物需要硼才能生长。然而，高含量的这种营养物质是有毒的，因此植物已经进化出改变吸收硼的速度，以优化不同环境中的生长。当土壤中硼含量很少时，某些转运蛋白会移动到根细胞表面，更有效地将硼带入根部。另一方面，当植物在高硼土壤中生长时，其根细胞表面的转运蛋白较少，以防止过多的硼进入植物。这种硼吸收调节似乎是合乎逻辑的，但有一个细节除外：在任何给定位置，土壤中硼的含量相对稳定，变化非常缓慢。为什么植物要投入能量来快速响应自然界变化如此缓慢的养分供应？索塔等人。使用数学和实验方法来研究拟南芥植物对硼的吸收。这项工作表明，植物快速改变硼进入根细胞的效率的能力实际上可以避免硼运输中的内部“交通堵塞”。如果根细胞表面转运蛋白的数量变化得更慢，单个细胞偶尔会经历高水平的硼，这会干扰硼进一步进入根部，导致堵塞。此外，这些硼“峰”可能会损害它们所影响的单个细胞。 Sotta 等人的研究结果。研究表明，通过快速改变根细胞表面某些转运蛋白的数量，植物可以确保它们获得稳定的硼供应。这项工作表明，为了开发能够适应不断变化的环境的人工系统，研究人员需要设计类似于植物中的解决方案，以避免系统中出现类似的交通拥堵。除了考虑植物如何与环境相互作用之外，研究它们如何避免养分吸收的内部交通拥堵可能有助于改变植物（包括农作物），使它们在恶劣的环境中生长得更好。
Nutrient uptake by roots often involves substrate-dependent regulated nutrient transporters. For robust uptake, the system requires a regulatory circuit within cells and a collective, coordinated behaviour across the tissue. A paradigm for such systems is boron uptake, known for its directional transport and homeostasis, as boron is essential for plant growth but toxic at high concentrations. In Arabidopsis thaliana, boron uptake occurs via diffusion facilitators (NIPs) and exporters (BORs), each presenting distinct polarity. Intriguingly, although boron soil concentrations are homogenous and stable, both transporters manifest strikingly swift boron-dependent regulation. Through mathematical modelling, we demonstrate that slower regulation of these transporters leads to physiologically detrimental oscillatory behaviour. Cells become periodically exposed to potentially cytotoxic boron levels, and nutrient throughput to the xylem becomes hampered. We conclude that, while maintaining homeostasis, swift transporter regulation within a polarised tissue context is critical to prevent intrinsic traffic-jam like behaviour of nutrient flow. Every multicellular organism, including all plants and animals, faces the challenge of taking up the nutrients it needs and distributing them throughout its body. Plants absorb many nutrients including nitrogen and boron from the soil into their roots, often using tightly controlled processes that require energy to work. Plant roots contain several distinct layers of cells and the nutrients need to cross these layers to reach a channel at the centre of the root known as the xylem, which transports the nutrients to other parts of the plant. Plants need boron to grow. However, high levels of this nutrient are toxic so plants have evolved to change the rate at which they absorb boron to optimize growth in different environments. When there is little boron in the soil, certain transporter proteins move to the surface of root cells to bring boron into the root more effectively. On the other hand, when plants grow in soils with high boron, their root cells have fewer of these transporters on their surfaces to prevent too much boron entering the plant. This regulation of boron uptake appears logical, except for one detail: at any given location, the amount of boron in the soil is relatively stable and changes only very slowly. Why do plants invest energy in responding rapidly to the supply of a nutrient that changes so slowly in nature? Sotta et al. used mathematics and experimental approaches to study boron uptake in a plant known as Arabidopsis. The work reveals that the plants ability to rapidly alter how efficiently boron moves into root cells actually serves to avoid internal “traffic jams” in boron transport. If the numbers of transporter proteins on the surface of root cells changed more slowly, individual cells would occasionally experience high levels of boron that would interfere with the movement of boron further into the root, causing a jam. Furthermore, these ‘peaks’ of boron could damage the individual cells they affect. The findings of Sotta et al. reveal that, by being able to rapidly change the numbers of certain transporter proteins on the surface of root cells, plants can ensure they receive a steady supply of boron. This work suggests that to develop artificial systems that can adapt to changing surroundings, researchers will need to engineer solutions like those found in plants in order to avoid similar traffic jams in the systems. Along with considering how plants interact with their environment, studying how they avoid internal traffic jams in nutrient uptake may help efforts to alter plants, including crops, so that they grow better in harsh environments.