Mitogens trigger cell division in animals. In plants, cytokinins, a group of phytohormones derived from adenine, stimulate cell proliferation. Cytokinin signaling is initiated by membrane-associated histidine kinase receptors and transduced through a phosphorelay system. We show that in the Arabidopsis shoot apical meristem (SAM), cytokinin regulates cell division by promoting nuclear shuttling of Myb-domain protein 3R4 (MYB3R4), a transcription factor that activates mitotic gene expression. Newly synthesized MYB3R4 protein resides predominantly in the cytoplasm. At the G2-to-M transition, rapid nuclear accumulation of MYB3R4—consistent with an associated transient peak in cytokinin concentration—feeds a positive feedback loop involving importins and initiates a transcriptional cascade that drives mitosis and cytokinesis. An engineered nuclear-restricted MYB3R4 mimics the cytokinin effects of enhanced cell proliferation and meristem growth.

促细胞分裂剂触发动物的细胞分裂。在植物中，细胞分裂素是一组源自腺嘌呤的植物激素，可刺激细胞增殖。细胞分裂素信号转导由膜相关组氨酸激酶受体启动，并通过磷酸继电器系统转导。我们表明在拟南芥中在芽顶端分生组织 (SAM) 中，细胞分裂素通过促进 Myb 结构域蛋白 3R4 (MYB3R4) 的核穿梭来调节细胞分裂，Myb 结构域蛋白 3R4 (MYB3R4) 是一种激活有丝分裂基因表达的转录因子。新合成的 MYB3R4 蛋白主要存在于细胞质中。在 G2 到 M 的转变中，MYB3R4 的快速核积累——与细胞分裂素浓度的相关瞬时峰值一致——提供了一个涉及输入蛋白的正反馈回路，并启动了驱动有丝分裂和胞质分裂的转录级联。工程化的核限制性 MYB3R4 模拟增强细胞增殖和分生组织生长的细胞分裂素作用。