A molecular breakthrough has shown that the dynamic change in root growth of plants plays an important role in their adjustment to soil conditions – and it's all controlled by hormones.

Professor Caroline Gutjahr, from the Technical University of Munich (TUM), and her team have been investigating how plant hormones influence the growth of roots, which are essential for reaching water and nutrients and for anchorage to the ground.

But, they are also sued for interacting and communicating with microorganisms in the soil. A long root enables the plant to reach deeper, more humid layers of soil, for example during drought. A shallower root with many root hairs is good for phosphate uptake, as phosphate is mostly found in the upper soil layers.

Prof Gutjahr and her colleagues have discovered new hormone interactions which influence the growth of plant roots.

“We found that the protein SMAX1 acts as molecular break for ethylene production,” she said. Ethylene is a plant hormone that is considered to trigger, or accelerate the ripening of many fruits and vegetables, but can also trigger other processes in plants.

If less of the gaseous hormone is produced by the plant, the plant is stimulated to grow long roots and short root hairs.

The suppressor SMAX1 can be removed by activating the so-called karrikin signaling pathway, which is triggered by another hormone. This switches on the production of ethylene, resulting in short primary roots and elongated root hairs.

This is the first time that scientists have succeeded in identifying and understanding a molecular process that is switched on by such a signaling pathway and has shown why it regulates a developmental process in plants.

Plant diversity is also reflected in molecular mechanisms “Surprisingly this mechanism has a significant impact on the roots of the legume lotus japonicus, the model plant for peas, beans and lentils, on which we conducted our research,” said Professor Gutjahr.

In contrast, the research team observed a much weaker influence in the roots of another model plant, arabidopsis thaliana, or thale cress, which is related to cabbage plants.

“This shows that the diversity of plants is not only reflected in their appearance, but also in the effect of their molecular triggers on growth,” the researcher concluded.

What's the relevance? “If we understand more precisely how root growth is regulated at the molecular level and in co-ordination with environmental stimuli, we can cultivate crops that are better able to cope with unfavorable environmental conditions and thus produce yield even under stress,” explained the scientist.

Her research group is now investigating how the identified hormone signaling pathways (karrikin and ethylene signaling) react to different environmental conditions. They hope to discover how these two signaling pathways collaborate with the sensors that allow plants to perceive various environmental influences to adjust root growth to benefit plant survival and yield.