Institute of Plant Biology and Zürich-Basel Plant Science Center, University of Zürich, Zollikerstrasse 107, CH-8008 Zürich, Switzerland.
Development. 2013 Nov;140(22):4544-53. doi: 10.1242/dev.098301.
The plant life cycle alternates between a diploid sporophytic and a haploid gametophytic generation. The female gametophyte (FG) of flowering plants is typically formed through three syncytial mitoses, followed by cellularisation that forms seven cells belonging to four cell types. The specification of cell fates in the FG has been suggested to depend on positional information provided by an intrinsic auxin concentration gradient. The goal of this study was to develop mathematical models that explain the formation of this gradient in a syncytium. Two factors were proposed to contribute to the maintenance of the auxin gradient in Arabidopsis FGs: polar influx at early stages and localised auxin synthesis at later stages. However, no gradient could be generated using classical, one-dimensional theoretical models under these assumptions. Thus, we tested other hypotheses, including spatial confinement by the large central vacuole, background efflux and localised degradation, and investigated the robustness of cell specification under different parameters and assumptions. None of the models led to the generation of an auxin gradient that was steep enough to allow sufficiently robust patterning. This led us to re-examine the response to an auxin gradient in developing FGs using various auxin reporters, including a novel degron-based reporter system. In agreement with the predictions of our models, auxin responses were not detectable within the FG of Arabidopsis or maize, suggesting that the effects of manipulating auxin production and response on cell fate determination might be indirect.
植物的生命周期在二倍体孢子体和单倍体配子体之间交替。有花植物的雌性配子体（FG）通常通过三个合胞有丝分裂形成，随后细胞化形成属于四个细胞类型的七个细胞。FG 中细胞命运的特化被认为取决于由内在生长素浓度梯度提供的位置信息。本研究的目的是开发数学模型来解释合胞体中这种梯度的形成。提出了两个因素来解释生长素梯度在拟南芥 FG 中的维持：早期的极性流入和后期的局部生长素合成。然而，在这些假设下，使用经典的一维理论模型无法产生梯度。因此，我们测试了其他假设，包括大中央液泡的空间限制、背景流出和局部降解，并研究了不同参数和假设下细胞特化的稳健性。没有一个模型产生足够陡峭的生长素梯度，从而无法实现足够稳健的模式形成。这促使我们使用各种生长素报告器（包括基于新型降解结构域的报告系统）重新检查发育中的 FG 对生长素梯度的反应。与我们模型的预测一致，在拟南芥或玉米的 FG 内检测不到生长素反应，这表明操纵生长素产生和反应对细胞命运决定的影响可能是间接的。
