Graduate School of Science and Technology, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan.
International Research Organization for Advanced Science and Technology, Kumamoto University, Kumamoto 860-8555, Japan.
Plant Physiol. 2018 Nov;178(3):1130-1141. doi: 10.1104/pp.18.00557. Epub 2018 Sep 5.
Root growth is controlled by mechanisms underlying cell division and cell elongation, which respond to various internal and external factors. In Arabidopsis (), cells produced in the proximal meristem (PM) elongate and differentiate in the transition zone (TZ) and the elongation/differentiation zone (EDZ). Previous studies have demonstrated that endoreplication is involved in root cell elongation; however, the manner by which cells increase in length by more than 2-fold remains unknown. Here, we show that epidermal and cortical cells in Arabidopsis roots undergo two modes of rapid cell elongation: the first rapid cell elongation occurs at the border of the proximal meristem and the TZ, and the second mode occurs during the transition from the TZ to the EDZ. Our previous study showed that cytokinin signaling promotes endoreplication, which triggers the first rapid cell elongation. Our cytological and genetic data revealed that the second rapid cell elongation involves dynamic actin reorganization independent of endoreplication. Cytokinins promote actin bundling and the resultant second rapid cell elongation through activating the signaling pathway involving the cytokinin receptors ARABIDOPSIS HISTIDINE KINASE3 (AHK3) and AHK4 and the B-type transcription factor ARABIDOPSIS RESPONSE REGULATOR2. Our results suggest that cytokinins promote the two modes of rapid cell elongation by controlling distinct cellular events: endoreplication and actin reorganization.
根的生长受到细胞分裂和细胞伸长机制的控制，这些机制会对外界和内部的各种因素做出反应。在拟南芥中，由近顶端分生组织（PM）产生的细胞在过渡区（TZ）和伸长/分化区（EDZ）伸长和分化。先前的研究表明，核内有丝分裂参与了根细胞的伸长；然而，细胞长度增加两倍以上的方式仍不清楚。在这里，我们表明拟南芥根表皮细胞和皮层细胞经历两种快速的细胞伸长模式：第一种快速细胞伸长发生在近顶端分生组织和过渡区的边界处，第二种模式发生在过渡区向伸长/分化区的转变过程中。我们之前的研究表明细胞分裂素信号促进核内有丝分裂，从而引发第一次快速细胞伸长。我们的细胞学和遗传学数据显示，第二种快速细胞伸长涉及到不依赖核内有丝分裂的动态肌动蛋白重组。细胞分裂素通过激活涉及细胞分裂素受体 ARABIDOPSIS HISTIDINE KINASE3 (AHK3) 和 AHK4 和 B 型转录因子 ARABIDOPSIS RESPONSE REGULATOR2 的信号通路，促进肌动蛋白的束集，从而引发第二次快速细胞伸长。我们的结果表明，细胞分裂素通过控制不同的细胞事件，即核内有丝分裂和肌动蛋白重组，来促进这两种快速细胞伸长模式。
