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How does a plant manage to quickly adapt its growth to changing environmental conditions? A research team at the University of Freiburg led by plant physiologist Prof. Dr. Jürgen Kleine-Vehn has discovered a previously unknown mechanism for this: A cellular degradation machinery acts in the background like a switch that decides whether the plant hormone auxin is available or not.

This mechanism enables the plant to respond to the environment and dynamically regulate its growth, whether it be root growth in the soil or shoot curvature toward the light. These results have been in the journal Science Advances.

At the heart of the newly discovered control mechanism are the so-called PILS proteins. They act like gatekeepers: sometimes they retain auxin inside the cell, sometimes they release it for growth. Which decision is made depends on how many of these proteins are present.

The Freiburg researchers have now been able to show that a cellular degradation machinery, known as ERAD machinery, regulates the number of PILS proteins as needed. If auxin is required due to changes in the environment, the gatekeepers are degraded and the plant changes its growth mode. Under stable conditions, however, the proteins remain in place and inhibit the hormone response.

"You can think of this mechanism as a molecular switch," says study leader Kleine-Vehn. "The plant decides whether auxin is effective or not, which thus flexibly adapts its growth to the environment." The discovery opens up a new perspective on the fine control of plant development. It shows how closely internal control mechanisms and external signals are interlinked.

Seinab Noura, a biologist at the University of Freiburg and first author of the study, also emphasizes the significance of the findings. "If we make targeted use of such mechanisms, crops could become more resistant to stress." In the long term, this knowledge could also help to make plants more robust against climate change, a key factor for sustainable agriculture in the future.