Parsimonious Model of Vascular Patterning Links Transverse Hormone Fluxes to Lateral Root Initiation: Auxin Leads the Way, while Cytokinin Levels Out
Parsimonious Model of Vascular Patterning Links Transverse Hormone Fluxes to Lateral Root Initiation: Auxin Leads the Way, while Cytokinin Levels Out
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DOI：
10.1371/journal.pcbi.1004450
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发表时间：
2015-10-01
影响因子：
4.3
通讯作者：
Grieneisen, Veronica A.
中科院分区：
文献类型：
--
作者：
el-Showk, Sedeer;Help-Rinta-Rahko, Hanna;Grieneisen, Veronica A.
生长素最大值位于拟南芥根尖的木质部轴沿着。该模式取决于生长素和细胞分裂素之间的相互反馈介导的PIN类生长素外排转运蛋白和AHP 6，细胞分裂素信号的抑制剂。这种相互作用已经被提出来调节激素各自信号结构域的大小和位置，并指定它们之间的不同边界。为了了解这个调控网络的动态，我们实现了一个简约的生长素运输的计算模型，认为激素调节生长素转运蛋白在空间背景下，明确考虑到细胞的形状和极性和细胞壁的存在。我们的分析表明，扩散产生的细胞分裂素水平的信息空间模式是一个理论上不太可能的情况。此外，我们的模型表明，这样的模式是不需要正确和强大的生长素图案。相反，生长素依赖的细胞分裂素反应的修改，而不是细胞分裂素水平的变化，允许必要的反馈，这可以放大和稳定生长素最大值。我们的模拟表明激素调节生长素流出模式的鲁棒性的重要性。虽然参与的PIN蛋白在血管图案是公认的，我们预测和实验验证的AUX 1和LAX 1/2生长素内流转运在这个过程中的作用。此外，我们表明，极性定位的PIN 1产生一个生长素通量电路，不仅稳定的木质部轴内的生长素的积累，但也提供了一种机制，生长素积累专门在木质部极周细胞，侧根启动的一个重要的早期步骤。该模型还揭示了相对木质部极上的周壁细胞竞争生长素积累，与侧根不是彼此相对起始的观察一致。
An auxin maximum is positioned along the xylem axis of the Arabidopsis root tip. The pattern depends on mutual feedback between auxin and cytokinins mediated by the PIN class of auxin efflux transporters and AHP6, an inhibitor of cytokinin signalling. This interaction has been proposed to regulate the size and the position of the hormones' respective signalling domains and specify distinct boundaries between them. To understand the dynamics of this regulatory network, we implemented a parsimonious computational model of auxin transport that considers hormonal regulation of the auxin transporters within a spatial context, explicitly taking into account cell shape and polarity and the presence of cell walls. Our analysis reveals that an informative spatial pattern in cytokinin levels generated by diffusion is a theoretically unlikely scenario. Furthermore, our model shows that such a pattern is not required for correct and robust auxin patterning. Instead, auxin-dependent modifications of cytokinin response, rather than variations in cytokinin levels, allow for the necessary feedbacks, which can amplify and stabilise the auxin maximum. Our simulations demonstrate the importance of hormonal regulation of auxin efflux for pattern robustness. While involvement of the PIN proteins in vascular patterning is well established, we predict and experimentally verify a role of AUX1 and LAX1/2 auxin influx transporters in this process. Furthermore, we show that polar localisation of PIN1 generates an auxin flux circuit that not only stabilises the accumulation of auxin within the xylem axis, but also provides a mechanism for auxin to accumulate specifically in the xylem-pole pericycle cells, an important early step in lateral root initiation. The model also revealed that pericycle cells on opposite xylem poles compete for auxin accumulation, consistent with the observation that lateral roots are not initiated opposite to each other.