Petal Power: New Gene Yields Unique Blossoms
Flowers of an experimental
Arabidopsis thaliana plant.
This plant has an altered
gene that gives its blooms
seven eye-catching petals,
rather than the usual four.
Tomorrow's flowers may produce blooms with a dazzling
profusion of petals. That's thanks to research at the Plant Gene Expression
Center, in Albany, California, where scientists have discovered the
petal-producing prowess of a gene namedappropriately enoughUltrapetala.
Their work could eventually result in unusual new flowers
for homes, parks, and offices. That should not only add new beauty to
our surroundings, but also create attractive opportunities for growers
and florists for new profits. Today, America's $11 billion floriculture
industry is one of the fastest growing segments of U.S. agriculture.
The Ultrapetala studies have yielded new clues not only about how plants form blooms, but also about how they form new shoots and other structures. All these plant parts originate from what are known as meristematic cells. These young cells grow rapidly, divide quickly, and eventually specialize, or differentiate, to form blossoms, leaves, or stems.
Ultrapetala findings may also apply to crop plants like corn and soybeans. "Ultrapetala and some of the genes with which it interacts," says ARS plant molecular geneticist Jennifer C. Fletcher, "appear to be key players in the architecture of green plants."
Molecular geneticist Jennifer
Fletcher inspects Arabidopsis
Small Plant, Big Results
Fletcher leads the Ultrapetala research. She did her experiments
using thale cress, or Arabidopsis thaliana. This little planta
relative of broccoli, cauliflower, cabbage, and brussels sproutshas
become the "lab rat" of plant biotechnology. One reason: Thale
cress has less genetic material than most other plants. Its relatively
small genome makes it somewhat easier for scientists to decipher the
structure and function of each of its genes.
In addition, A. thaliana is easy to grow in research greenhouses,
using familiar nursery flats. It develops quickly from a seed to a fully
mature, 8- to 16-inch-high plant in a mere 4 to 6 weeks.
In her laboratory and greenhouse experiments, Fletcher has produced
and investigated unique A. thaliana plants. Some have as many as 10
creamy white petals instead of the usual 4. Too, other structures differed,
likely because of the interaction of Ultrapetala with other genes
Fletcher is analyzing. The test plants, for instance, also boasted shoots
that were wider and more numerous than those of everyday thale cress
and produced more flowers.
For these tests, Fletcher soaked A. thaliana seeds in ethyl methanesulfonate. That changed the makeup of the Ultrapetala gene. Then she grew several generations of plants from these seeds. This technique, widely used in modern molecular biology, can yield plants with significant internal and external differences. These differences can help scientists pinpoint the roles that a gene plays in its natural, unaltered state.
Wild Arabidopsis thaliana
flowers typically have four
|New Plants Proffer More Petals
A basic example from Fletcher's work: The chemically treated A.
thaliana seeds produced plants with an altered form of Ultrapetala
inside. All those plants had more petals than untreated plants. This
strongly suggests that Ultrapetala has a key role in dictating
the number of petals a plant forms.
Fletcher designed other tests to reveal more about the relation of
Ultrapetala to genes already known to affect key steps of a plant's
development. She interbred her plants with experimental thale cress
that had altered forms of these other interesting genes. Those genes
included Era1 (short for enhanced response to abscissic acid,
a plant hormone); Pan (for perianthia, a botanical term); and
Clv1, Clv2, and Clv3 (short for clavata, the clublike
structure that these experimental plants form to enclose their seeds).
She found that Era1 apparently shares some functions with Ultrapetala. They both regulate the number of green, leaflike structurescalled sepalsthat enclose the developing flower buds. Pan and Ultrapetala appear to have a common role in controlling the number of growing sites, or nodes, from which new flowers develop.
| Plants with altered Clv1,
Clv2, and Clv3, when crossed with the altered Ultrapetala plants,
yielded A. thaliana that had extremely enlarged stems. Investigations
using high-tech scanning electron and confocal microscopes showed that
these stems contained normal-size meristematic cells. But there were more
of them, resulting in the added height and width.
Ultrapetala and these genes, notes Fletcher, regulate where
and how meristematic cells accumulate. That's how they control the size
of stems, the number of sepals and petals, and other structural features.
In new studies, funded by ARS and the National Science Foundation,
Fletcher will investigate mechanisms called signal transduction pathways.
Ultrapetala and other genes use these pathways to control the
fate of cells, determining, for example, whether a meristematic cell
will differentiate into a sepal or petal.
Interest in deciphering these sequential chemical steps has heated
up in the past two decades, but much more remains to be learned. "We
know so much about how to grow a plant," says Fletcher, "but
so little about how a plant grows."
Fletcher's recent Ultrapetala findings and, earlier, her clavata
work have been published in top scientific journals, including Science
and Development. Additional details are available on the World Wide
Web at www.pgec.usda.gov/fletcher/jfresearch.html.
The Plant Gene Expression Center is jointly operated by the Agricultural
Research Service and the University of California at Berkeley.By
Agricultural Research Service Information Staff.
This research is part of Plant, Microbial, and Insect Genetic Resources,
Genomics, and Genetic Improvement (#301) and Plant Biological and Molecular
Processes (#302), two ARS National Programs described on the World Wide
Web at www.nps.ars.usda.gov.
"Petal Power: New Gene Yields Unique Blossoms" was published in the May 2003 issue of Agricultural Research magazine.