Tucker Matthew R, Hinze Annika, Tucker Elise J, Takada Shinobu, Jürgens Gerd, Laux Thomas
Faculty of Biology, Schaenzlestrasse 1, University of Freiburg, D-79104 Freiburg, Germany.
Development. 2008 Sep;135(17):2839-43. doi: 10.1242/dev.023648. Epub 2008 Jul 24.
Stem cells are maintained in an undifferentiated state by signals from their microenvironment, the stem cell niche. Despite its central role for organogenesis throughout the plant's life, little is known about how niche development is regulated in the Arabidopsis embryo. Here we show that, in the absence of functional ZWILLE (ZLL), which is a member of the ARGONAUTE (AGO) family, stem cell-specific expression of the signal peptide gene CLAVATA3 (CLV3) is not maintained despite increased levels of the homeodomain transcription factor WUSCHEL (WUS), which is expressed in the organising centre (OC) of the niche and normally promotes stem cell identity. Tissue-specific expression indicates that ZLL acts to maintain the stem cells from the neighbouring vascular primordium, providing direct evidence for a non-cell-autonomous mechanism. Furthermore, mutant and marker gene analyses suggest that during shoot meristem formation, ZLL functions in a similar manner but in a sequential order with its close homologue AGO1, which mediates RNA interference. Thus, WUS-dependent OC signalling to the stem cells is promoted by AGO1 and subsequently maintained by a provascular ZLL-dependent signalling pathway.
干细胞通过来自其微环境（即干细胞龛）的信号维持未分化状态。尽管干细胞龛在植物整个生命周期的器官发生中起着核心作用，但对于拟南芥胚胎中干细胞龛的发育如何受到调控却知之甚少。在此我们表明，在缺乏作为AGO（AGO蛋白家族）家族成员的功能性ZWILLE（ZLL）时，尽管同源异型域转录因子WUSCHEL（WUS）的水平有所增加，但信号肽基因CLAVATA3（CLV3）的干细胞特异性表达仍无法维持，WUS在干细胞龛的组织中心（OC）表达，通常促进干细胞特性。组织特异性表达表明ZLL的作用是维持来自相邻维管原基的干细胞，这为非细胞自主机制提供了直接证据。此外，突变体和标记基因分析表明，在茎尖分生组织形成过程中，ZLL以类似方式起作用，但其作用顺序与其密切同源物AGO1不同，AGO1介导RNA干扰。因此，AGO1促进WUS依赖的OC向干细胞的信号传导，随后由依赖前维管组织ZLL的信号通路维持。
