January 21, 2022

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Science: Cytokinins regulate the division mechanism of plant stem cells

Science: Cytokinins regulate the division mechanism of plant stem cells


Science: Cytokinins regulate the division mechanism of plant stem cells.  Researchers from the University of Cambridge in the United Kingdom and the California Institute of Technology in the United States have discovered a mechanism by which a plant hormone called cytokinin controls cell division. This breakthrough discovery has greatly improved our understanding of how plants grow. The relevant research results were published online on February 25, 2021 in the journal Science, with the title of the paper “Molecular mechanism of cytokinin-activated cell division in Arabidopsis”.

Science: Cytokinins regulate the division mechanism of plant stem cells
Arabidopsis, picture from Wikipedia.

Cell division is the basis of all life forms: all multicellular organisms, including plants and animals, form a complex organism by dividing a single cell billions of times. Undifferentiated stem cells in plants act as a reservoir of new cells, from which plants can grow and develop special tissues. The new stems, new leaves, new roots, and new flowers all come from a small group of stem cells in the growth area called apical meristem.

The cells in these growth areas divide continuously in a process called mitosis, resulting in the structure of the plant. Scientists have long known that cytokinin is the core of these cell division behaviors, but they do not know how it stimulates cell proliferation.

In this paper, these authors discovered for the first time how cytokinins activate stem cell division in plants. They used Arabidopsis thaliana, a member of the mustard family commonly used in plant scientific research, as a model organism to reveal that cytokinins directly promote the transport of the transcription factor MYB3R4 from the cytoplasm to the nucleus, where it activates the expression of key cell cycle genes.

Dr. Weibing Yang, the first author of the paper, said, “Understanding how stem cell self-renewal is controlled is essential to understanding plant growth and development. We know that cytokinins are important, and our research now explains the mechanism by which cytokinins regulate stem cell division- –It transports proteins to the nucleus, where it activates genes involved in mitosis.”

Co-author of the paper and Dr. Raymond Wightman, Manager of Imaging Core Facilities at Sainsbury Laboratory, added, “Using time-lapse confocal microscopy of living plants, we can capture the cellular dynamics of proteins that are important for triggering mitosis.”

Dr. Yang explained, “Time-lapse confocal microscopy observations of single cells revealed rapid changes in the position of MYB3R4 protein. Before cell division, this protein is mainly in the cytoplasm. At the beginning of mitosis, MYB3R4 accumulates rapidly in the nucleus. After the completion of cell division, the protein is transported back to the cytoplasm. For more than 40 years, it has been known that the level of plant endogenous cytokinin fluctuates during the cell cycle and reaches a peak during the G2/M transition period. We are now It was confirmed that the direct response of this cytokinin peak was the input of MYB3R4 into the nucleus.”

Further experiments showed that cytokinin functions as a “molecular switch”, which triggers a positive feedback loop—it promotes the nuclear localization of MYB3R4 to activate the transcription of importin encoding genes IMPA3 and IMPA6 , And the transcription of IMPA3 and IMPA6 in turn promoted the nuclear import of MYB3R4. Professor Henrik Jönsson, the co-corresponding author of the paper, said, “Through mathematical modeling, we have confirmed that this positive feedback can make MYB3R4 nuclear transport faster and stronger.”

Dr. Yang added, “Our findings may have practical applications. By mutating the nuclear export signal, we were able to design a constitutively nuclear-localized MYB3R4 protein and found that it can greatly enhance stem cell proliferation and meristem. The tissue grows, thereby partially mimicking the effect of cytokinin treatment.”

Professor Elliot Meyerowitz, the co-corresponding author of the paper, said, “The increase in cytokinin in the shoot apex meristem is one of the results of increasing root nitrogen nutrients. It can increase the cytokinin in this meristem and the cell division response may provide A way for plants to grow as if they were well fertilized, even if the nitrogen level in the soil is not ideal.”

By giving people a deeper understanding of how plant cells divide during growth, basic plant science research like this research can help determine new ways to enhance plant growth and lay the foundation for future research work that affects plant health and agricultural yields .


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