Shimadzu Shunji, Yonekura Takaaki, Furuya Tomoyuki, Kojima Mikiko, Ishizaki Kimitsune, Asahina Masashi, Ohashi-Ito Kyoko, Sakakibara Hitoshi, Fukaki Hidehiro, Fukuda Hiroo, Kondo Yuki
Department of Biological Sciences, Graduate School of Science, The University of Osaka, Osaka, Japan.
Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan.
Nat Plants. 2025 Aug 4. doi: 10.1038/s41477-025-02051-4.
Wood is formed as plants expand in thickness through radial growth, which initiates after apical growth. At the onset of radial growth, dormant procambial cells in the vasculature become active and act as bifacial cambium stem cells, which produce xylem (wood) inward and phloem outward. Cytokinin has been implicated in radial growth initiation; however, its precise mechanisms, especially at the cellular level, remain unclear. Here we show a switching mechanism of radial growth, in which a cytokinin response maximum (CRM) transiently appearing in roots beyond the meristem induces stem cell activation. Manipulation of the CRM revealed that procambial cells primarily retain phloem differentiation competence but newly acquire xylem differentiation and self-renewal capabilities upon experiencing the CRM. Transcriptome analysis and mathematical modelling showed that the CRM is driven by cytokinin production and subsequent positive and negative signalling feedback loops. Our findings therefore demonstrate that a dynamic hormone response establishes multipotent stem cells de novo by providing proper competences to undifferentiated cells arising from the meristematic tissue, enabling the post-embryonic growth transition. This mechanism may serve as the basis for the vitality of plants, which continue to grow vigorously even after embryogenesis.
随着植物通过径向生长使茎干变粗，木材得以形成，径向生长在顶端生长之后开始。在径向生长开始时，维管系统中休眠的原形成层细胞变得活跃，充当双面形成层干细胞，向内产生木质部（木材），向外产生韧皮部。细胞分裂素与径向生长的起始有关；然而，其确切机制，尤其是在细胞水平上，仍不清楚。在这里，我们展示了一种径向生长的转换机制，其中在分生组织以外的根中短暂出现的细胞分裂素反应最大值（CRM）诱导干细胞激活。对CRM的调控显示，原形成层细胞主要保留韧皮部分化能力，但在经历CRM后新获得木质部分化和自我更新能力。转录组分析和数学建模表明，CRM由细胞分裂素产生以及随后的正负信号反馈回路驱动。因此，我们的研究结果表明，动态激素反应通过为分生组织产生的未分化细胞提供适当的能力，从头建立多能干细胞，从而实现胚胎后生长转变。这一机制可能是植物活力的基础，植物即使在胚胎发生后仍能继续茁壮成长。
