By Anna Groner, Checkbiotech

Researchers in the U.K. and the U.S. have identified a long sought key player in plant development and growth. Could this start a new biotech boom?

A fundamental difference between flora and fauna is the inability of plants to move. This is the reason why growing plants need to adapt to their environment, and are much more sensitive to light and temperature than animals. Moreover, plants harbor specific molecules, so called plant hormones, which help them coordinate their development to the level of a single cell.

One very important member of the plant hormone family are the auxins. These molecule are involved in many specific processes of plant growth and development, such as stem growth towards the light or root growth in the opposite direction. Equally important, auxin also helps plants flower and bear fruit.

Since the discovery of auxin over 70 years ago, the exact mechanism of how auxin is perceived in plants remains unclear. However, two research teams headed by Mark Estelle (Indiana University, Bloomington) and Ottoline Leyser (University of York, U.K.) shed light on this enigma. The two articles published by the groups in the May 26 issue of Nature, identify the long-sought molecule which directly interacts with auxin in Arabidopsis thaliana (Wall Cress).

Their results show that auxin binds to a receptor called TIR1. Receptors usually transmit signals within cells, such as growth signals in the case of auxin. Upon auxin binding, the receptor TIR1 becomes an active part of a complex of molecules called SCF. SCF then has the ability to mediate the degradation of another set of proteins, which usually prevent the activation of auxin regulated processes. This elimination then sets off specific auxin regulated processes.

This mechanism is called “de-repression” since upon the elimination of the auxin repressors - which usually prevent the onset of the effect of auxin - auxin regulated processes can set in.

“To establish precisely how [auxin is perceived], the two teams first spent several years running down a lot of blind alleys,” Estelle told Nature. “It turned out that the pathway was a lot simpler than assumed,” Leyser added.

This is because in general, cellular signalling mechanisms, when activated by plant hormone perception, are much more complex and require the involvement of several components before an action, such as plant growth, is carried out. This complexity has the advantage of being fine tuned, since every molecule involved in this signalling cascade can be viewed as a signal regulating step.

However, short signalling pathways have the advantage of quickly being able to induce responses. Therefore, probably with the help of auxin, environmental conditions can quickly be perceived, and if favorable, plant growth and development can be activated.

Judy Callis commented on this important finding in the same Nature issue by starting her article with an old nursery rhyme, “Oats and beans and barley grow, Oats and beans and barley grow, Can you, or I, or anybody know, How oats and beans and barley grow?”

Further she stated, “Even without knowing how auxins work, people have long used them in agriculture as safe and effective agents for weed control, and in horticulture, for example to promote root development in cuttings. In the case of weed controls, the adage ‘too much of a good thing’ applies – too much of auxin and plants die.”

Since important information on the mechanism of plant auxin perception now has been found, researchers might be able to better predict the effects of auxin. For the future, this could lead to new or more sophisticated agricultural or biotech applications.

Consistent with this notion, Judy Callis ends her article by saying, “Much remains to be done. Can the interaction of auxins and SCF account for the myriad auxin responses in growth and development? Let us hope that we will soon be able to answer the rhyme: ‘yes, you and I can know how oats and beans and barley grow’!”

Anna Groner is a Science Journalist for Checkbiotech and has finished her diploma degree in Molecular Biology at the University of Basel, Switzerland. Her major area of interest include results and outlooks in biomedical research. Contact her at Anna.Groner@stud.unibas.ch.

The F-box protein TIR1 is an auxin receptor
Nihal Dharmasiri, Sunethra Dharmasiri and Mark Estelle
Nature 2005


The Arabidopsis F-box protein TIR1 is an auxin receptor
Kempinski and Leyser
Nature 2005