Solved mystery: How do plant cells know when they stop growing?
There was one Long enigma in biology: How do cells know how big they are?
The answer, it turns out, was hidden inside Robert Sablowski’s computer files, collecting virtual dust since 2013. “I had the data for years and years, but I was not looking the right way,” says Sablowski, a biologist. plant cells at the John Innes Center in Norwich, England. For a previous project, he had been investigating a protein called KRP4. By melting it with a jellyfish fluorescent protein to make it glow, Sablowski could study it inside a plant cell, but he had no idea it would be the key to understanding cell size regulation.
For organisms to evolve, their cells must undergo a pattern of growth, DNA replication, and division. But scientists studying this process, known as the cell cycle, have long noticed that divisions are not necessarily identical – cells often divide asymmetrically and their size is corrected somewhat later. In one study published in science last month, Sablowski and his colleagues discovered how plants are doing this: Cells use their DNA as a kind of measuring cup. While the discovery was made by studying a factory called Arabidopsis, can have far-reaching implications for understanding cell size regulation in animals and humans, and may even affect the future of crop production.
Identifying how cells estimate their size has been complicated because most cellular proteins scale to the size of the cell itself. Sablowski compares the situation to trying to measure yourself with your arm. “You can’t do it because your arm grows in proportion to your body,” he says. “You need an external reference to know how big you are.” What does not change as the cell grows is its DNA. Scientists have long speculated that a cell could use its DNA as a kind of indicator to estimate its size, but Sablowski’s team is the first to show evidence of this process.
“It has been a profound mystery for many, many decades in biology, how cells are able to accomplish this task, knowing almost magically how big they are,” says Martin Howard of the John Innes Center, who helped developing the mathematical models necessary for progress. Shape and size regulation are important because they are closely related to how a cell works: Too large and it can be difficult for the cell to quickly obtain the information contained in its own DNA; very small and the cell does not have enough space to divide properly, causing errors in division and growth that can lead to disease.
Arabidopsis is actually a bad grass, according to Sablowski, but is considered a model organism in plant biology because it is easy to grow and ripens quickly. This means that it has already been well studied by other researchers in the field. “The community for Arabidopsis has been critical, “says Marco D’Ario, a graduate student at the John Innes Center who created and helped carry out the experiment.” The same experimental installation that took us three or four years – without the community, would have wanted to ease from 10 to 15 “.
The team grew Arabidopsis in the pot for about six weeks, then chopped on the small top of the plant, the part where new leaves and flowers appear, to observe its continuous growth under a microscope. They can track, at about 1,000X magnification, the location and size of each cell at the apex of growth at different stages of the cell cycle. Sablowski and D’Ario traded shifts, checking cells every other hour for two days. “We had the equipment, we had the material. “We just had to roll up our sleeves and do the 48-hour experiment to get data that no one else had,” says Sablowski.