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Mystery Solved: How Plant Cells Know When to Stop Growing

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It was a long-standing enigma in biology: How do cells know how big they are?

The answer, it turns out, has been hidden in Robert Sablowski’s ordinary papers, collecting virtual dust since 2013. “I’ve had the data for years and years, but I didn’t look in the right way,” says Sablowski, a biologist. plant cells at the John Innes Center in Norwich, England. For a previous project, I had investigated a protein called KRP4. Fused with a jellyfish fluorescent protein to make it shine, Sablowski could study it in a plant cell, but he had no idea it would be the key to understanding the regulation of cell size.

For organisms to grow, their cells must undergo a pattern of growth, DNA replication, and division. But scientists studying this process, known as the cell cycle, have long understood that divisions are not necessarily identical – cells often divide asymmetrically, and their size is somehow corrected later. In a study published in Science last month, Sablowski and colleagues revealed how plants do this: cells use their own DNA as a sort of measuring cup. While the discovery was being made studying a plant called Arabidopsis, could have broad implications for understanding the regulation of cell size in animals and humans, and may even influence the future of crop production.

Identifying how cells assess their size has been complicated, because most cellular proteins scale with the size of the cell itself. Sablowski confronts the situation as he tries to measure himself with your arm. “You can’t do that, because your arm grows in proportion to your body,” he says. “You need an outside reference to know how big you are.” What doesn’t change when the cell grows, is its DNA. Scientists have long speculated that a cell could use its DNA as a sort of indicator to measure its size, but Sablowski’s team is the first to show evidence of this process.

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“It’s been a deep mystery for many, many decades in biology, how cells are able to accomplish this task of magically knowing what their size is,” says Martin Howard of the John Innes Center, who helped develop the models. mathematics necessary to advance it. The regulation of shape and size is important because they are closely linked to the functioning of a cell: They are too large and it can be difficult for the cell to quickly retrieve information contained in its own DNA; too small and the cell does not have enough space to divide properly, causing errors in division and growth that could lead to disease.

Arabidopsis it is actually a weed, according to Sablowski, but is considered a model organism in plant biology because it is easy to grow and matures quickly. This means that it has already been well studied by other researchers in the field. “The community for Arabidopsis it was critical, ”says Marco D’Ario, a graduate student at the John Innes Center who conceived and helped do the experiment.“ The same experimental installation that took us three or four years — without the community, would have easily taken 10 to 15. ”

The team grows Arabidopsis in pots for about six weeks, then cut off the small growth tip of the plants, the part where new leaves and flowers emerge, to observe their continued growth under the microscope. They can track, at about a 1,000X magnification, the location and size of each cell at the growing tip at different stages of the cell cycle. Sablowski and D’Ario exchanged shifts, checking cells every other hour for two days. “We had the equipment, we had the equipment. We just needed to roll up our sleeves and do the 48-hour experiment to get the data that no one else had, ”says Sablowski.


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