Plant scientists discover on/off switch for plants' response to hormones

Scientists from Wageningen University & Research and their Japanese and Spanish colleagues have found an 'on/off' switch and a 'volume knob' in plants that control plant growth. The application of this discovery can help growers design new crops that are, for example, more resistant to diseases, drought or floods. Their findings have been published in Nature Plants.

The team of researchers has shown that the very complex response of plants to the plant hormone auxin can be reduced to a simple switching model. Basically, the auxin turns a switch from 'off' to 'on'. At the same time, a second factor competes with this 'switch' and thus determines how sensitive each cell is to the hormone. The many ways in which a plant responds to auxin, from root to flowering, is determined, so to speak, by the on/off switch and the volume control.

The small auxin molecule is known to control many aspects of plant growth and development by altering the activity of various genes. DNA-binding ARF proteins bind to genes and turn them on or off. It is the auxin that determines whether the ARF proteins are active or not. Most plants have different ARF proteins, which have been formed because multiple copies have been created during evolution, after which their properties have changed. All this leads to an extremely complex web of ARF proteins that can cause different reactions to one hormone.

The team studied the response to auxin in the umbrella moss Marchantia polymorpha. This plant has the simplest auxin system, and was previously described by the researchers in a publication in eLife, for which Hirotaka Kato and Sumanth Mutte received the Wageningen Research Award in 2019. In this new research Nature Plants the team takes advantage of the simplicity of the Marchantia reaction system and has meticulously mapped its functioning using a combination of genetics and protein biochemistry. This revealed the simple system of two competing ARF proteins that forms the essence of the auxin system.

ARF1 protein in Marchantia – The on/off switch is marked with a fluorescent protein (photo: Shubhajit Das)

Fundamental change of perspective

“We think that our results will fundamentally change the way researchers look at the functioning of the important auxin hormone,” says Dolf Weijers, head of the Laboratory for Biochemistry and leader of the research team. “Moreover, this major leap in our knowledge of how cells respond to the hormone gives us unprecedented opportunities to influence the response of crops to the hormone at the cellular level. Multiplication, root growth and many other properties of plants depend on the response to auxin.”

Deceived by complexity

For decades it was believed that flowering plants, including the model plant thale cress, use a very complex system of response factors to make cells respond in different ways to the same hormone. Thus, some cells grow, others divide, and still others differentiate. It was also believed that the same hormone causes root development and flowering, depending on where in the plant the reaction occurs.

The research team now describes how they discovered a very simple principle that underlies the complex responses to the plant hormone auxin. It is likely that this same principle applies to other plant species that possess large families of ARF proteins. Current research teaches us how plants, including crops, respond to the hormone.

Experimental biologist Hirotaka Kato, formerly at Wageningen University, now at Kobe University, collaborated on his groundbreaking research with colleagues at the Wageningen Laboratory of Chemistry and Biophysics, the Alba Synchrotron in Barcelona and the University of Kyoto. The research was partly financed with an NWO-VICI grant that was awarded to Dolf Weijers in 2015.

 

Source: https://www.wur.nl/nl/show/plantenwetenschappers-ontdekken-aanuit-knop-voor-reactie-van-planten-op-hormoon.htm