By Tracey Peake
Researchers at North Carolina State University have pinpointed a small
group of genes responsible for "telling" plants when, where and how to
produce a hormone that is key to their development. Their findings shed
light on the ways in which hormone production in plants affects both a
plant's growth and its ability to adapt to changing environments.
Dr. Jose Alonso, assistant professor of genetics, and a team of
geneticists and plant biologists from NC State, Germany and the Czech
Republic conducted the research. Their findings are published in the April 4
edition of the journal Cell.

Plant growth and development are regulated by a small number of
hormones, which plants combine in various ways so that they can adapt to and
thrive in changing environmental conditions. Auxin and ethylene are two of
the most important of these growth-regulating hormones.

Scientists had previously established that plants respond differently
to ethylene depending upon the type of plant tissue it is applied to, the
developmental stage of the plant, and the surrounding environmental
conditions. They also knew that the presence of auxin, another key
growth-regulator, often served as a "trigger" for a plant to produce more
ethylene, but were unsure of the ways in which auxin was synthesized.

"Auxin controls almost every process in a plant," Alonso says, "and so
it's very important to understand how and why auxin is produced within the
plant."

In order to find out more about how auxin production is triggered, the
NC State team identified a mutant strain of Arabidopsis - or mustard weed -
that had a root system insensitive to the growth inhibitory effect of
ethylene.

When the team looked at the genome of this mutant strain of mustard
weed, they discovered that its lack of response to ethylene was due to the
changes in a gene that they named TAA1. This gene produces a protein that is
necessary for auxin synthesis. In a normal plant, the TAA1 gene recognizes
the presence of ethylene as its signal to make proteins that in turn
synthesize auxin, which controls growth.

The researchers found that if the TAA1 gene and two other related
genes were "knocked out" or inactive, the plant had 50 percent less auxin
than normal.

Their findings are the first to definitively establish a relationship
between a particular family of genes, tissue-specific ethylene response, and
auxin production in plants.

"If we want to do intelligent manipulation of plants, to breed them so
that they ripen at a certain rate, or so that they're well-adapted to
particular environments, then we need to understand more about the ways that
these hormones interact or 'talk' to each other," Alonso says. "This
research gives us concrete evidence for at least one way in which this
happens."


[news.ncsu.edu]