Molecular mechanism of cytokinin-activated cell division in Arabidopsis

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.

Automated summary

Mitogens trigger cell division in animals, while in plants, cytokinins derived from adenine stimulate cell proliferation. Cytokinin signaling in Arabidopsis SAM is shown to regulate cell division by promoting nuclear shuttling of MYB3R4, a transcription factor activating mitotic gene expression. Rapid nuclear accumulation of MYB3R4 at G2-to-M transition, associated with a peak in cytokinin concentration, initiates a transcriptional cascade driving mitosis and cytokinesis, mimicking the effects of enhanced cell proliferation and meristem growth.