New Biosensor Lets Us See Life as Never Before

A plant hormone produced in the stem tip plays a vital role in the coordination of many growth and behavioral processes in plant life cycles — it is called auxin.

From embryonic development to the growth of roots, auxin attaches itself to the specific receptors in the nucleus of a cell, which leads to an activation of signaling that coordinates the plant's response to the simulations from outside.

Now, scientists at the Max Planck Institute for Developmental Biology in Tübingen and the University of Bayreuth have devised a tool that provides real-time visualization of the auxin in living plant cells.

This is a remarkable discovery since, almost 100 years after the effects of auxin were first described, it can now be viewed for the first time. The researchers were able to view the redistribution of auxin using a new biosensor, according to the study published in Nature.

Making use of fluorescence

The study describes the tool, dubbed AuxSen, as based on the E. coli tryptophan repressor, which is a transcription factor involved in regulating amino acid metabolism. This is the binding pocket of which is engineered to be specific to auxin. The researcher's goal was to visualize auxin distribution by having plants that produce a protein that glows when auxin is present. 

When the auxin-binding group was joined with the selected fluorescent proteins, researchers were able to achieve a readout as a fluorescence resonance energy transfer signal.

This enabled researchers to achieve real-time monitoring of auxin concentrations through the lifespan of a plant via AuxSen. 

"We have shown that both increases and decreases of auxin concentration can be visualized in tissue in real-time, which was not possible before. In addition, AuxSen reveals auxin in subcellular areas to which other, indirect auxin reporters have no access. The goal now is to improve the possible applications to other biological problems by optimizing expression systems and using fluorescent proteins with different characteristics. We are now providing the necessary material to the scientific community," the two senior authors Birte Höcker and Gerd Jürgens wrote.

According to the researchers, the technological breakthrough has many potential applications, but first and foremost, scientists can now better understand the auxin's physiological effects.