Department of Plant Molecular Biology, University of Lausanne-Sorge, Lausanne 1015, Switzerland.
Proc Natl Acad Sci U S A. 2010 Mar 16;107(11):5214-9. doi: 10.1073/pnas.0910772107. Epub 2010 Feb 8.
The endodermis is a root cell layer common to higher plants and of fundamental importance for root function and nutrient uptake. The endodermis separates outer (peripheral) from inner (central) cell layers by virtue of its Casparian strips, precisely aligned bands of specialized wall material. Here we reveal that the membrane at the Casparian strip is a diffusional barrier between the central and peripheral regions of the plasma membrane and that it mediates attachment to the extracellular matrix. This membrane region thus functions like a tight junction in animal epithelia, although plants lack the molecular modules that establish tight junction in animals. We have also identified a pair of influx and efflux transporters that mark both central and peripheral domains of the plasma membrane. These transporters show opposite polar distributions already in meristems, but their localization becomes refined and restricted upon differentiation. This "central-peripheral" polarity coexists with the apical-basal polarity defined by PIN proteins within the same cells, but utilizes different polarity determinants. Central-peripheral polarity can be already observed in early embryogenesis, where it reveals a cellular polarity within the quiescent center precursor cell. A strict diffusion block between polar domains is common in animals, but had never been described in plants. Yet, its relevance to endodermal function is evident, as central and peripheral membranes of the endodermis face fundamentally different root compartments. Further analysis of endodermal transporter polarity and manipulation of its barrier function will greatly promote our understanding of plant nutrition and stress tolerance in roots.
内皮层是高等植物共有的一种根细胞层，对于根的功能和养分吸收具有重要意义。内皮层通过其凯氏带（Casparian strips）将外层（外周）与内层（中央）细胞层分隔开来，凯氏带是由特殊壁材料精确排列而成的带。在这里，我们揭示了凯氏带处的膜是中央和外周质膜区域之间的扩散屏障，并且它介导与细胞外基质的附着。因此，该膜区域的功能类似于动物上皮中的紧密连接，尽管植物缺乏在动物中建立紧密连接的分子模块。我们还鉴定了一对流入和流出转运蛋白，它们标记质膜的中央和外周区域。这些转运蛋白在分生组织中已经表现出相反的极性分布，但在分化过程中其定位变得更加精细和受限。这种“中央-外周”极性与 PIN 蛋白在同一细胞内定义的顶端-基底极性共存，但利用不同的极性决定因素。中央-外周极性在早期胚胎发生中就可以观察到，它揭示了静止中心前体细胞内的细胞极性。在动物中，极性区域之间的严格扩散阻断很常见，但在植物中从未被描述过。然而，它与内皮层功能的相关性是显而易见的，因为内皮层的中央和外周膜面临着根本不同的根区室。对内皮层转运蛋白极性的进一步分析及其屏障功能的操纵将极大地促进我们对植物根系营养和胁迫耐受性的理解。
