Dynamic patterns of the plant growth regulator auxin

植物发育过程中最具影响力的信使是微小的生长调节剂生长素。植物激素控制着细胞分裂和细胞生长等基本过程，并在茎结构和叶脉管系统的基础上以模式积累。因此，生长素控制着植物的动态形态。生长素及其载体PIN和AUX/LAX的模式在植物发育过程中是动态重组的。生长素模式建模的悠久历史最近经历了一次重置，因为直到那时神秘的PIN极性被发现可能是由发育组织内产生的机械应力协调的。这一发现提示了生长素/PIN和组织力学之间的反馈循环。细胞中高浓度的生长素软化相邻细胞壁，从而在组织内产生机械应力。机械应力反过来反馈生长素流动，因为PIN结合沿应力细胞壁上调。组织力学在生长素的形成中起着重要的作用，细胞的几何形状和生物力学在组织中的变化也是如此。细胞几何形状和生物力学变化对生长素模式的影响有多大，这是一个悬而未决的问题。为了解决这个重要的问题，我们在这里提出通过实时成像预测生长素在分割组织上的模式动态，并将模型预测与实验观察进行比较，来研究细胞几何和生物力学变化对生长素模式的作用。特别地，我们将利用生长素动力学中的自然变异性导致初始细胞选择，以两个具有高生长素浓度的相邻细胞为标志，以确定细胞几何形状在生长素模式动力学中的作用。此外，我们将利用侧根形成过程中覆盖的内胚层的关键和众所周知的力学变化作为生物力学变化对生长素模式的作用的案例研究。这两个案例研究将与来自Maizel实验室（P6）的实验数据进行密切反馈，并将进一步允许我们探索细胞分裂如何影响组织力学和生长素模式。Lohmann实验室（P5）研究了茎尖分生组织中细胞几何结构的变化，为测试细胞几何结构对生长素模式的影响提供了一个独立的组织几何结构。理论建模和实验观察的前所未有的密切互动将为生长素模式动力学和我们对植物组织力学和生化信号在植物发育过程中如何相互交织的理解提供新的基准。

The most influential messenger during plant development is the tiny growth regulator auxin. The phytohormone controls basic processes like cell division and cell growth, and accumulates in patterns underlying the shoot architecture and the leaf vasculature. Thereby auxin controls the dynamic morphology of plants. The patterns of auxin and its carriers PIN and AUX/LAX are dynamic and reorganize throughout plant development. The long history of modelling auxin patterns has recently experienced a reset as the up to then mystical PIN polarity was uncovered to be likely coordinated by mechanical stresses arising within the developing tissue. This finding now suggests the following underexplored feedback cycle between auxin/PIN and tissue mechanics. High auxin concentration in a cell softens adjacent cell walls thereby generating mechanical stresses within the tissue. Mechanical stresses in return feed back on auxin flows as PIN binding is upregulated along stressed cell walls. As tissue mechanics plays a fundamental role in auxin patterning so does cell geometry and biomechanical variations across a tissue. How much cell geometry and biomechanical variation impact auxin patterning is an open question.To address this important question, we here propose to investigate the role of cell geometry and biomechanical variation on auxin patterning by predicting auxin patterning dynamics on segmented tissues from live imaging, and by comparing model predictions to experimental observations. In particular, we will use the natural variability in the auxin dynamics leading up to founder cell selection, marked by two adjacent cells with high auxin concentration, to identify the role of cell geometry in auxin patterning dynamics. Further, we will employ the pivotal and well-known mechanical changes of the overlaying endodermis during lateral root formation as a case study for the role of biomechanical variations across a tissue on auxin patterning. Both case studies will be performed in close feed back with experimental data from the Maizel lab (P6) and will further allow us to explore how cell divisions impact tissue mechanics and auxin patterning. Exploring the variation in cell geometry at the shoot apical meristem as investigated by the Lohmann lab (P5) will provide an independent tissue geometry to test for the impact on cell geometry on auxin patterning. The unprecedented close interaction of theoretical modelling and experimental observations will provide a new benchmark for auxin patterning dynamics and our understanding of how plant tissue mechanics and biochemical signalling are intertwined during plant development.