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2-Plants: Scientists discover genetic key to growing hardier, more productive plants



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   "U.S. patents currently are pending and a research licensing
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------------------------------- GENET-news -------------------------------

TITLE:  Scientists discover genetic key to growing hardier, more
        productive plants
SOURCE: University of Connecticut, USA / Eurekalert
        http://www.eurekalert.org/pub_releases/2005-10/uoc-sdg100405.php
DATE:   6 Oct 2005

------------------ archive:  http://www.genet-info.org/ ------------------


Scientists discover genetic key to growing hardier, more productive plants
Findings, to be published in Oct. 7 Science, may prompt textbook changes

STORRS, Conn. - A team of scientists led by University of Connecticut
plant biologist Roberto Gaxiola has discovered an overlooked genetic key
to generating plants that are more productive, more drought resistant and
can grow in soils low in nutrients. Their work is the first to
successfully test in cells a 30-year-old hypothesis that explains the
movement of a primary growth and development hormone through plants and
is expected to prompt biology textbooks to be rewritten.

The researchers from UConn, Purdue University and Pennsylvania State
University determined that one of three proton pumps found within plant
cells, previously believed to have an extremely limited function, plays a
critical role in plant root and shoot system growth and development by
controlling cell division, expansion and hormone transport. Over-
expressing the single gene that encodes this particular proton pump
significantly enhances the transportation of the primary plant growth
hormone, auxin, and results in plants with stronger, more extensive root
systems and as much as 60 percent more foliage, the researchers report in
the Oct. 7 issue of the prestigious journal Science.

"This discovery has the potential to revolutionize agriculture
worldwide," said Gaxiola, an assistant professor-in-residence in UConn's
plant science department. "This over-expression regulates the development
of one of the most important parts of the plant, the roots. A plant with
larger roots is a healthier and more productive plant, because, with a
larger root system, the plant is able to get water and nutrients from
larger soil areas.

"Biology textbooks tell you there are three pumps inside a plant's cell
but one is less important. Our research shows that is not the case,"
Gaxiola said. "As it turns out, that tiny pump is required to shuttle the
master pump, the plant's major engine, to the plasma membrane. That, in
turn, allows the master pump to facilitate the transport of more of the
growth hormone, auxin, through the plant's plasma membrane and through
the plant's root and shoot systems, resulting in enhanced cell division
and growth."

All plants contain three proton pumps - a master pump, known as the P-
type H+-ATPase, that facilitates transport of nutrients in and out of
plant cells, and two other pumps that work within plant cells. Biologists
have shown that only the P-type H+-ATPase pumps protons into the space
outside the cell to create changes that drive the transport of small
molecules in and out of cells. Until now, they believed the AVP1 H+-PPase
that Gaxiola's group over-expressed merely controlled pH levels within
plant vacuoles, or large storage areas inside plant cells, and served
primarily as a back-up pump to a larger vacuolar pump known as V-ATPase.
Scientists believed that the larger vacuolar pump was the only one to
help shuttle the master pump to and from the plant cell's plasma membrane.

In collaboration with scientists at the Massachusetts Institute of
Technology and Harvard University, Gaxiola previously had created plants
in which the AVP1 gene was over-expressed using the research plant
Arabidopsis thaliana. As Gaxiola predicted, these plants were salt- and
drought-resistant and sequestered more salt ions in their vacuoles.
Surprisingly the plants also had abnormally large root and shoot systems.

Simon Gilroy, a Pennsylvania State University cell biologist, provided
another piece to the puzzle when he discovered that the pH, which
indicates proton concentration, was unchanged inside the cells. But the
extra-cellular pH was lower, meaning it was more acidic and had a higher
proton concentration.

The next clue came from plant cell biologist Angus Murphy and his
colleagues at Purdue University.

"When Simon reported the acidity and the proton gradient was increased
between the inside and outside of plant cells in Roberto's over
expression lines, we saw an opportunity to test the model that had been
used to explain the transport of the plant hormone auxin for the last 30
years," Murphy said. "This model predicts that an increased proton
gradient should result in a faster rate of auxin transport. This theory
never had been tested directly tested in plants where the proton gradient
had been manipulated by molecular genetic techniques. When we determined
that the rate of transport was increased, but the overall auxin content
was not, the auxin transport model was validated."

They determined AVP1's critical role by comparing the transgenic plants
to both ordinary Arabidopsis plants and mutant versions of the plant that
were devoid of AVP1. They discovered that the AVP1 mutants didn't develop
functional root systems and their shoots were tiny and deformed.

Gaxiola specializes in manipulating plant proton pumps for crop
improvement and relied on Murphy and Purdue colleague Wendy Peer, for
expertise in auxin transport in plants, and Gilroy for expertise in plant
cell biology with an emphasis on roots.

Additional authors are UConn doctoral students Jisheng Li, Haibing Yang,
Soledad Undurraga and Mariya Khodakovskaya; Purdue doctoral students
Joshua Blakeslee, Anindita Bandyopadhyay, Boosaree Tiapiwantakun,
Elizabeth Richards; Penn State doctoral student Gregory Richter; and
University of South Carolina Biology Professor Beth Krizek.

Gaxiola said that early experiments to duplicate the Arabidopsis results
in other crops, such as tomatoes, rice, cotton and poplar trees, indicate
the team's discovery could have implications for increasing the world's
food production and aiding global reforestation efforts. He predicts that
within the next five years there will be a "boom" of crops genetically
engineered using his team's approach. The research team's findings are
likely to be particularly significant for farmers in developing
countries, including Gaxiola's native Mexico, because many live in arid
regions and lack irrigation systems and money for the amount of expensive
fertilizers needed to feed plants with less expansive root systems.

U.S. patents currently are pending and a research licensing agreement
with an international company has been signed.

###

For a copy of the embargoed Science paper, please contact the American
Association for the Advancement of Sciences Office of Public Programs at
(202) 326-6440 or scipak@aaas.org.


Contact:
Beth Krane beth.krane@uconn.edu
860-486-4656 University of Connecticut




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