Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA.
Proc Natl Acad Sci U S A. 2012 Mar 6;109(10):4002-7. doi: 10.1073/pnas.1200636109. Epub 2012 Feb 15.
The transcription factor WUSCHEL (WUS) acts from a well-defined domain within the Arabidopsis thaliana shoot apical meristem (SAM) to maintain a stem cell niche. A negative-feedback loop involving the CLAVATA (CLV) signaling pathway regulates the number of WUS-expressing cells and provides the current paradigm for the homeostatic maintenance of stem cell numbers. Despite the continual turnover of cells in the SAM during development, the WUS domain remains patterned at a fixed distance below the shoot apex. Recent work has uncovered a positive-feedback loop between WUS function and the plant hormone cytokinin. Furthermore, loss of function of the cytokinin biosynthetic gene, LONELY GUY (LOG), results in a wus-like phenotype in rice. Herein, we find the Arabidopsis LOG4 gene is expressed in the SAM epidermis. We use this to develop a computational model representing a growing SAM to suggest the plausibility that apically derived cytokinin and CLV signaling, together, act as positional cues for patterning the WUS domain within the stem cell niche. Furthermore, model simulations backed by experimental data suggest a previously unknown negative feedback between WUS function and cytokinin biosynthesis in the Arabidopsis SAM epidermis. These results suggest a plausible dynamic feedback principle by which the SAM stem cell niche is patterned.
转录因子 WUSCHEL（WUS）在拟南芥茎尖分生组织（SAM）的一个明确界定的区域内发挥作用，以维持干细胞龛。涉及 CLAVATA（CLV）信号通路的负反馈回路调节 WUS 表达细胞的数量，并为干细胞数量的动态平衡维持提供了当前范例。尽管在发育过程中 SAM 中的细胞不断更新，但 WUS 结构域仍以固定的距离模式化在茎尖下方。最近的工作揭示了 WUS 功能与植物激素细胞分裂素之间的正反馈回路。此外，细胞分裂素生物合成基因 LONELY GUY（LOG）的功能丧失会导致水稻出现 wus 样表型。在此，我们发现拟南芥 LOG4 基因在 SAM 表皮中表达。我们利用这一点来开发一个代表生长中的 SAM 的计算模型，以表明由顶端衍生的细胞分裂素和 CLV 信号共同作为干细胞龛内 WUS 结构域模式化的位置线索的合理性。此外，基于实验数据的模型模拟表明，在拟南芥 SAM 表皮中，WUS 功能和细胞分裂素生物合成之间存在以前未知的负反馈。这些结果表明了一种合理的动态反馈原则，通过该原则对 SAM 干细胞龛进行模式化。
