Plants harbour ancient, ultra-fast responsiveness

During the lockdown, people rediscovered retro practices en masse, such as baking their own bread, preserving and propagating plants, albeit with modern tools. Nowadays, for example, rooting powder helps plants that struggle to establish roots. A pinch of it on the cutting edge promotes root development. The secret ingredient? The naturally occurring plant hormone auxin, which influences nearly all processes related to growth and development in plants, including root growth.

Modifying building blocks

Within a few seconds of contact with the plant hormone auxin, as found in rooting powder, plants undergo changes at the molecular level. This discovery was made by André Kuhn, a researcher in the Biochemistry department. Professor Dolf Weijers explains: “These rapid responses cannot be attributed to changing genetic activity, as is the case with all previously studied growth processes.” The study shows that the plant hormone stimulates plants to modify previously produced proteins, a process that is considerably faster than the conventional DNA transcription process, which takes at least ten minutes. "This happens on a massive scale," says Weijers. "Within ten minutes, the cell adjusts five percent of all its proteins."

The modification involves adding a small molecule with a negative charge, a phosphate group. It may seem like a subtle change, but such a mark has a significant impact. “It can activate a protein or send it to the cell's trash bin, or alter the interaction between two proteins,” Weijers summarises. As proteins are the building blocks of life, this alters the cell's functioning and, consequently, the plant's operation. The principle is comparable adapting building blocks of a Lego house. If you discard some of them, stick random blocks together or click others loose, the house will look different.

Millions of years old

Researchers discovered that the ultra-fast reaction occurs not only in land plants, but also in algae. “Algae and plants share a common, single-celled ancestor that lived about 700 million years ago,” explains Weijers. This suggests that the rapid response system was likely present in that ancestor and has persisted in evolution since then. Notably, the single-celled ancestor, unlike plants, did not produce auxin. But the hormone was present in nature; about half of bacteria produce it. "Perhaps the ancestor of plants and algae used the mechanism to detect bacteria-produced auxin and rapidly respond to bacteria in the environment," the professor speculates. In any case, there was a role for the plant hormone auxin long before plants began producing it as a hormone.

Secrets under the hood

The discovery of this ancient mechanism by Kuhn, Weijers and their colleagues provides new insights into the plant growth hormone auxin. They hope that this newfound knowledge encourages scientists to look at the plant hormone in a different light. Since its discovery in Utrecht a hundred years ago, plant scientists worldwide have been studying the hormone and its influence on plant growth and development. “While those researchers wait for hours for something to happen at the DNA level, the plant has already modified thousands of proteins,” says Weijers. All of this is orchestrated by a mechanism that is more than half a billion years old. "There's a lot more happening under the hood of plants than we always thought," concludes Weijers.