The Casparian strip (CS) constitutes a physical diffusion barrier to water and nutrients in plant roots, which is formed by the polar deposition of lignin polymer in the endodermis tissue. The precise pattern of lignin deposition is determined by the scaffolding activity of membrane-bound Casparian Strip domain proteins (CASPs), but little is known of the mechanism(s) directing this process. Here, we demonstrate that Endodermis-specific Receptor-like Kinase 1 (ERK1) and, to a lesser extent, ROP Binding Kinase1 (RBK1) are also involved in regulating CS formation, with the former playing an essential role in lignin deposition as well as in the localization of CASP1. We show that ERK1 is localized to the cytoplasm and nucleus of the endodermis and that together with the circadian clock regulator, Time for Coffee (TIC), forms part of a novel signaling pathway necessary for correct CS organization and suberization of the endodermis, with their single or combined loss of function resulting in altered root microbiome composition. In addition, we found that other mutants displaying defects in suberin deposition at the CS also display altered root exudates and microbiome composition. Thus, our work reveals a complex network of signaling factors operating within the root endodermis that establish both the CS diffusion barrier and influence the microbial composition of the rhizosphere.

中文翻译：

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拟南芥内胚层根组织所需的新型信号通路塑造了根际微生物组。

里海带（CS）构成了对植物根部水分和养分的物理扩散屏障，这是由木质素聚合物在内胚层组织中的极性沉积形成的。木质素沉积的确切模式是由膜结合的里海带状结构域蛋白（CASPs）的支架活性决定的，但对指导这一过程的机理了解甚少。在这里，我们证明内胚层特异性受体样激酶1（ERK1），以及在较小程度上，ROP结合激酶1（RBK1）也参与调节CS的形成，前者在木质素沉积以及在CASP1的本地化中。我们显示ERK1定位于内胚层的细胞质和细胞核，并与生物钟调节器，咖啡时间（TIC），形成内在皮层的正确CS组织和干化所必需的新型信号传导途径的一部分，它们的单一或联合功能丧失导致根部微生物组组成发生改变。此外，我们发现其他突变体在CS的Suberin沉积中显示出缺陷，也显示出改变的根系分泌物和微生物组组成。因此，我们的工作揭示了一个复杂的信号传导因子网络，该信号传导因子在根部内胚层中起作用，既可建立CS扩散屏障，又可影响根际的微生物组成。我们发现，其他突变体在CS的Suberin沉积中显示出缺陷，也显示出改变的根系分泌物和微生物组组成。因此，我们的工作揭示了一个复杂的信号传导因子网络，该信号传导因子在根部内胚层中起作用，既可建立CS扩散屏障，又可影响根际的微生物组成。我们发现，其他突变体在CS的Suberin沉积中显示出缺陷，也显示出改变的根系分泌物和微生物组组成。因此，我们的工作揭示了一个复杂的信号传导因子网络，该信号传导因子在根部内胚层中起作用，既可建立CS扩散屏障，又可影响根际的微生物组成。