Department of Plant Science, University of Manitoba, Winnipeg, R3T 2N2 Manitoba, Canada.
Plant Sci. 2012 Jul;190:40-51. doi: 10.1016/j.plantsci.2012.04.002. Epub 2012 Apr 7.
Arabidopsis shoot meristem activity is regulated by a molecular network involving the participation of several components, including SHOOTMERISTEMLESS (STM), CLAVATA1 (CLV1), and ZWILLE (ZLL). In an effort to identify the role of these genes during in vitro shoot formation Brassica and Arabidopsis plants were transformed with the Brassica napus (Bn) STM, CLV1, ZLL1 and ZLL2 identified in previous work [1]. In both systems shoot organogenesis was promoted by the over-expression of BnSTM, BnZLL1, and BnZLL2, and repressed by the over-expression of BnCLV1. This distinct regulation, analogous to that occurring during in vivo meristem formation where STM and ZLL encourage stem cell formation while CLV1 accelerates transition to differentiation, suggests similar regulatory mechanisms governing shoot formation in vivo and in vitro. While the BnZLL1 and BnZLL2 induction of shoot organogenesis correlated only to changes in auxin signaling, BnSTM and BnCLV1 evoked major transcriptional alterations in cytokinin response. Besides increasing the transcript levels of two cytokinin receptors, ARABIDOPSIS HISTIDINE KINASE4 (AHK4) and CYTOKININ INDEPENDENT KINASE (CKI1), ectopic expression of BnSTM induced Type-B ARABIDOPSIS RESPONSE REGULATORS (ARRs) and repressed Type-A ARRs. Opposite transcriptional patterns occurred in explants over-expressing BnCLV1, characterized by a decreased ability to produce shoots. The role played by Type-A and Type-B ARRs during shoot organogenesis was further examined using a genetic approach which revealed the requirement of ARR12 for the BnSTM positive regulation of shoot organogenesis. Collectively these results expand our knowledge on the function of meristem genes, and provide new tools for enhancing in vitro propagation systems.
拟南芥茎分生组织的活性受一个分子网络调控，该网络涉及到几个组成部分的参与，包括茎分生组织维持蛋白（STM）、CLAVATA1（CLV1）和 ZWILLE（ZLL）。为了鉴定这些基因在离体芽形成过程中的作用，我们在前期工作中鉴定出的油菜（Bn）STM、CLV1、ZLL1 和 ZLL2 转化了拟南芥和油菜植物[1]。在这两个系统中，过表达 BnSTM、BnZLL1 和 BnZLL2 促进了芽器官的形成，而过表达 BnCLV1 则抑制了芽器官的形成。这种独特的调控作用与体内分生组织形成过程中的调控作用相似，其中 STM 和 ZLL 促进干细胞的形成，而 CLV1 加速向分化的转变，这表明在体内和体外芽形成过程中存在类似的调控机制。虽然 BnZLL1 和 BnZLL2 诱导芽器官的形成仅与生长素信号的变化相关，但 BnSTM 和 BnCLV1 引起了细胞分裂素反应的主要转录改变。除了增加两个细胞分裂素受体（ARABIDOPSIS HISTIDINE KINASE4（AHK4）和 CYTOKININ INDEPENDENT KINASE（CKI1）的转录本水平外，BnSTM 的异位表达还诱导了 B 型拟南芥响应调节剂（ARRs），并抑制了 A 型 ARRs。在过表达 BnCLV1 的外植体中发生了相反的转录模式，其特征是产生芽的能力降低。通过遗传方法进一步研究了 A 型和 B 型 ARRs 在芽器官形成过程中的作用，结果表明 ARR12 是 BnSTM 正向调控芽器官形成所必需的。总之，这些结果扩展了我们对分生组织基因功能的认识，并为增强离体繁殖系统提供了新的工具。
