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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?
July 2005 by Anna Groner, Checkbiotech.

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.

Nihal Dharmasiri, Sunethra Dharmasiri and Mark Estelle, The F-box protein
TIR1 is an auxin receptor, Nature 2005:
[www.ncbi.nlm.nih.gov]
stract&list_uids=15917797&query_hl=3

Kempinski and Leyser, The Arabidopsis F-box protein TIR1 is an auxin
receptor, Nature 2005:
[www.ncbi.nlm.nih.gov]
stract&list_uids=15917798&query_hl=1

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