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2-Plants: U.S. scientists may produce drought-resistant GE plants



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TITLE:  Gene may produce drought-resistant plants
SOURCE: Purdue University, USA, Press Release
        http://news.uns.purdue.edu/html4ever/030521.Jenks.wax2.html
DATE:   May 21, 2003

------------------ archive: http://www.gene.ch/genet.html ------------------


Gene may produce drought-resistant plants

WEST LAFAYETTE, Ind. - The identification and duplication of a gene that
controls production of plants' outermost protective coating may allow
Purdue University researchers to create crops with increased drought
resistance.

Scientists cloned the gene WAX2 after they discovered a fast-wilting
mutant of Arabidopsis , a commonly used experimental plant. The gene is
directly associated with the synthesis of the protective layer of plants,
called the cuticle, and its contained waxes, according to the study
published in the May issue of The Plant Cell.

The difference in the mutant Arabidopsis when compared to a wild-type, or
normal, plant is the plants' ability to retain water. This is apparently
because the mutation, called wax2, has a different cuticle structure than
found in a plant that has the normal gene, WAX2.

"If we can alter the expression of the WAX2 gene, we might be able to
produce a cuticle that is thicker or more rigid so that it's less
permeable to water loss," said Matt Jenks, associate professor of
horticulture and landscape architecture.

Manipulating what the gene does or when it is turned on could result in
plants better able to survive in arid conditions.

Jenks and his research team isolated more than 20 mutant Arabidopsis
plants that showed alterations in the amount of wax they produced. Of
these, only a few lost water more quickly than the wild type.

"The mutant wax2 was the most drought susceptible," Jenks said. "Unlike
previously described wax mutants, removal of the WAX2 gene product causes
dramatic alteration in the cuticle membrane, and the plant no longer is
able to prevent water loss."

Jenks said he believes that when the cuticle membrane structure is
changed because of the wax2 malfunction of the WAX2 gene, the protective
wax within the cuticle membrane is displaced, affecting transpiration.
Transpiration is how plants emit waste matter though their leaf surfaces.

"It's likely that the cuticle meshwork is disrupted so the wax molecules
no longer stack properly within the cuticle," he said. "The plant becomes
very permeable to water and overall is less able to withstand drought
conditions."

The study using the mutant wax2 also revealed unique interactions between
the cuticle and other aspects of plant development.

The researchers found that the wax2 mutant has fewer stomata, the small
holes in the plant's surface that regulate water loss. This mutant also
has a male sterility problem that prevents pollen from activating the
stigma, where reproduction begins.

"The cloning of WAX2 is providing evidence that lipids in the cuticle may
serve as signals that control how plants develop," Jenks said. "Lipids in
animals are known to play important roles in regulating development, but
lipid signaling in plants is not well understood."

Lipids are water-insoluble molecules that aid in various cell metabolic
functions.

"We want to understand the genetics and biochemistry of plant cuticle
production so that ultimately we may be able to modify economically
important crops to grow better during drought" he said.

The other authors of the study are postdoctoral student Xinbo Chen,
visiting professor Xionglun Liu, and graduate students S. Mark Goodwin
and Virginia Boroff, all of the Purdue Department of Horticulture and
Landscape Architecture.

The U.S. Department of Agriculture National Research Initiative and
Purdue University provided support for the research.

Writer: Susan A. Steeves, (765) 496-7481, ssteeves@aes.purdue.edu
Source: Matthew Jenks, (765) 494-1332, jenks@hort.purdue.edu
Ag Communications: (765) 494-2722; Beth Forbes, bforbes@aes.purdue.edu;
http://www.agriculture.purdue.edu/AgComm/public/agnews/


Related Web sites:
Purdue Horticulture
National Science Foundation
USDA


PHOTO CAPTION Research conducted at Purdue University by Matt Jenks with
Arabidopsis plants may lead to the development of more drought-resistant
plants. Jenks is an assistant professor of horticulture. (Purdue
Agricultural Communication photo/Tom Campbell)

A publication-quality photograph is available at ftp://ftp.purdue.edu/
pub/uns/jenks.wax2.jpeg.

ABSTRACT

Cloning and Characterization of the WAX2 Gene of Arabidopsis Involved in
Cuticle Membrane and Wax Production

Xinbo Chen, S. Mark Goodwin, Virginia L. Boroff, Xionglun Liu, and
Matthew A. Jenks 1 - Department of Horticulture and Landscape
Architecture, Purdue University, West Lafayette, Indiana 47907

Insertional mutagenesis of Arabidopsis ecotype C24 was used to identify a
novel mutant, designated wax2, that had alterations in both cuticle
membrane and cuticular waxes. Arabidopsis mutants with altered cuticle
membrane have not been reported previously. Compared with the wild type,
the cuticle membrane of wax2 stems weighed 20.2 percent less, and when
viewed using electron microscopy, it was 36.4 percent thicker, less
opaque, and structurally disorganized. The total wax amount on wax2
leaves and stems was reduced by 78 percent and showed proportional
deficiencies in the aldehydes, alkanes, secondary alcohols, and ketones,
with increased acids, primary alcohols, and esters. Besides altered
cuticle membranes, wax2 displayed postgenital fusion between aerial
organs (especially in flower buds), reduced fertility under low humidity,
increased epidermal permeability, and a reduction in stomatal index on
adaxial and abaxial leaf surfaces. Thus, wax2 reveals a potential role
for the cuticle as a suppressor of postgenital fusion and epidermal
diffusion and as a mediator of both fertility and the development of
epidermal architecture (via effects on stomatal index). The cloned WAX2
gene (verified by three independent allelic insertion mutants with
identical phenotypes) codes for a predicted 632--amino acid integral
membrane protein with a molecular mass of 72.3 kD and a theoretical pI of
8.78. WAX2 has six transmembrane domains, a His-rich diiron binding
region at the N-terminal region, and a large soluble C-terminal domain.
The N-terminal portion of WAX2 is homologous with members of the sterol
desaturase family, whereas the C terminus of WAX2 is most similar to
members of the short-chain dehydrogenase/reductase family. WAX2 has 32
percent identity to CER1, a protein required for wax production, but not
for cuticle membrane production. Based on these analyses, we predict that
WAX2 has a metabolic function associated with both cuticle membrane and
wax synthesis. These studies provide new insight into the genetics and
biochemistry of plant cuticle production and elucidate new associations
between the cuticle and diverse aspects of plant development.


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