A receptor-like kinase mutant with absent endodermal diffusion barrier displays selective nutrient homeostasis defects.
A receptor-like kinase mutant with absent endodermal diffusion barrier displays selective nutrient homeostasis defects.
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DOI：
10.7554/elife.03115
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发表时间：
2014-09-16
期刊：
影响因子：
7.7
通讯作者：
Geldner N
中科院分区：
文献类型：
--
作者：
Pfister A;Barberon M;Alassimone J;Kalmbach L;Lee Y;Vermeer JE;Yamazaki M;Li G;Maurel C;Takano J;Kamiya T;Salt DE;Roppolo D;Geldner N
内皮层是植物根细胞外扩散的主要屏障，是目前植物养分吸收模型的核心。尽管如此，人们对建立这种内胚层屏障的基因知之甚少。在这项研究中，我们报告了一个强屏障突变体，schengen 3（sgn 3）的鉴定和表征。我们观察到一个令人惊讶的能力的突变体，以维持营养平衡，但表现出一个重大的缺陷，在维持足够水平的常量营养素钾。我们发现SGN 3/GASSHO 1是一种受体样激酶，它是将内胚层分化的主要参与者--卡斯帕里亚条域蛋白（CASPs）定位成一个不间断的环状结构域所必需的。SGN 3似乎定位于更宽的条带中，嵌入不断增长的CASP微域。SGN 3的发现有力地推进了我们询问植物营养稳态机制的能力，并为内胚层质膜上局部微区的形成提供了一种新的参与者。http://dx.doi.org/10.7554/eLife.03115.001植物的根在土壤中寻找矿物质和水，但它们也必须提供一个屏障，阻止这些营养物质从植物中泄漏出来，阻止微生物入侵和引起疾病。内胚层是一层内层细胞，围绕着沿着根中部的静脉，在幼根中起着这样一种屏障的作用。排斥水分的聚合物沉积在几乎所有维管植物（包括蕨类植物、针叶树和开花植物）的根细胞之间，在内皮周围形成一个称为“凯氏带”的带。这条带密封了年轻的根，并阻止水通过植物细胞之间的间隙移动，但仍然允许矿物质，营养物质和水通过根细胞运输到植物中。然而，这种结构的重要性还有待测试，由于缺乏突变体植物没有凯氏带。Pfister等人现在报告说，在模式植物拟南芥中，删除编码一种名为SCHENGEN 3的蛋白质的基因，会导致凯氏带被不规则大小的洞打断。这种蛋白质通常以高水平存在于根内皮层中，在那里它嵌入细胞膜中。Pfister等人还表明，如果没有SCHENGEN 3蛋白，其他称为CASPs的蛋白质-通常在根细胞周围形成凯氏带的地方标记出条纹-只能以不连续的斑块积累。进一步的实验表明，删除SCHENGEN 3基因不会在将CASP蛋白递送到细胞膜方面引起一般性问题;相反，它会特异性地阻止CASP蛋白形成单一的不间断条带。出乎意料的是，破坏凯氏带似乎并没有妨碍根的许多功能。突变植物仍然可以吸收水分和养分，而且突变植物的叶子中除了钾之外，许多必需矿物质的含量都是正常的。这种矿物质的水平在没有SCHENGEN 3蛋白的突变体植物中要低得多。Pfister等人认为，在缺乏完整凯氏带的植物中，钾不断从根部泄漏到土壤中。这些发现表明，至少在拟南芥中，凯氏带在帮助植物吸收和积累水分和养分方面可能没有以前认为的那么重要。现在需要进一步开展工作，以发现可能能够弥补这一结构损失的未知备份系统。DOI：http://dx.doi.org/10.7554/eLife.03115.002网站
The endodermis represents the main barrier to extracellular diffusion in plant roots, and it is central to current models of plant nutrient uptake. Despite this, little is known about the genes setting up this endodermal barrier. In this study, we report the identification and characterization of a strong barrier mutant, schengen3 (sgn3). We observe a surprising ability of the mutant to maintain nutrient homeostasis, but demonstrate a major defect in maintaining sufficient levels of the macronutrient potassium. We show that SGN3/GASSHO1 is a receptor-like kinase that is necessary for localizing CASPARIAN STRIP DOMAIN PROTEINS (CASPs)—major players of endodermal differentiation—into an uninterrupted, ring-like domain. SGN3 appears to localize into a broader band, embedding growing CASP microdomains. The discovery of SGN3 strongly advances our ability to interrogate mechanisms of plant nutrient homeostasis and provides a novel actor for localized microdomain formation at the endodermal plasma membrane. DOI: http://dx.doi.org/10.7554/eLife.03115.001 Plant roots forage in the soil for minerals and water, but they must also provide a barrier that stops these nutrients leaking back out of the plant and stops microbes invading and causing disease. The endodermis—an inner layer of cells that surrounds the veins that run along the middle of a root—acts as such a barrier in young roots. Polymers that repel water are deposited between the cells in the roots of almost all vascular plants—which include ferns, conifers, and flowering plants—to form a band around the endodermis called the ‘Casparian strip’. This strip seals off the young roots and stops water moving through the gaps between plant cells, but still allows minerals, nutrients, and water to be transported through the root cells and into the plant. However, the importance of this structure has yet to be tested due to the lack of mutant plants without a Casparian strip. Pfister et al. now report that deleting the gene that encodes a protein called SCHENGEN3 in the model plant Arabidopsis thaliana causes the Casparian strip to be interrupted by irregularly sized holes. This protein is normally found at high levels in the root endodermis, where it is embedded into the cell membranes. Pfister et al. also showed that without the SCHENGEN3 protein, other proteins called CASPs—that normally mark out a stripe around the root cells where the Casparian strip will form—only accumulated in discontinuous patches. Further experiments revealed that deleting the gene for SCHENGEN3 does not cause general problems in delivering the CASP proteins to the cell membrane; instead, it specifically stops the CASP proteins from forming a single, uninterrupted stripe. Unexpectedly, disrupting the Casparian strip did not appear to hinder many of the functions of a root. The mutant plants could still take up water and nutrients, and the leaves of mutant plants had normal levels of many essential minerals—with the exception of potassium. The level of this mineral was much lower in mutant plants without the SCHENGEN3 protein. Pfister et al. suggest that in plants that lack an intact Casparian strip, potassium is continuously leaked from the root into the soil. These findings reveal that in Arabidopsis, at least, the Casparian strip might not be as important as once thought for helping the plant to take up and accumulate water and nutrients. Further work is now needed to uncover the as yet unknown backup systems that might be able to compensate for the loss of this structure. DOI: http://dx.doi.org/10.7554/eLife.03115.002