Daily University Science News
Biologists
have discovered how to genetically convert leaves into petals,
an achievement that may be the botanical equivalent of the medieval
alchemists' dream of transmuting iron into gold.
In a cover
article in the February issue of Current Biology, the University
of California, San Diego scientists show that a new class of floral
genes which they recently discovered, together with three other
genes responsible for flower development, are sufficient to convert
leaves into petals.
"This
is a very exciting discovery," notes Martin F. Yanofsky,
a professor of biology at UCSD who conducted the study with UCSD
biologist Soraya Pelaz in collaboration with Rosalinda Tapia-Lopez
and Elena R. Alvarez-Buylla of the National Autonomous University
of Mexico in Mexico City. "We've known for a decade how to
convert the flower organs into leaves, but we haven't been able
to convert leaves into flower organs. We knew we were missing
a piece of the puzzle and now we know exactly what we were missing."
The team's
discovery has important commercial as well as scientific implications.
"It means
that we should be able to convert leaves of essentially any plant
into petals, which could certainly make for some very interesting
looking plants," adds Yanofsky. "Imagine, for example,
a long-stemmed rose in which the many leaves along the stem are
each converted into colorful petals."
Normal flowers
consist of a series of four rings or "whorls." The outermost
whorl is made up of sepals, the green leaf-like organ that normally
surrounds the flower bud before it opens.
Inside the
sepals is a ring of petals, then a ring of stamens, the male reproductive
structures, and at the center are the carpels (often referred
to as the pistils), the female reproductive structures.
More than
200 years ago, biologists proposed that the sepal, petal, stamen
and carpel organs that make up a typical flower represent modified
leaves. But despite rapid progress by researchers around the world
over the past decade in isolating key flower-control genes, no
one had been able to convert leaves into each of the flower organs.
Last May,
Yanofsky and his colleagues at UCSD published a paper in Nature
describing their discovery that a trio of identical genes, when
mutated in concert, produce an abnormality that had been known
for 2,000 years, but which scientists had never before understood.
This abnormality,
prized within the flower industry and known as a "double
flower," results when the petals, stamens and carpels of
the flower are all converted into sepals.
The UCSD scientists
discovered that this reiterative process of producing a flower
within a flower within a flower continues indefinitely in plants
with a trio of mutated SEP genes -- or at least until the smallest
organs of the flower can't be detected. Many roses, camellias
and impatiens, as well as a host of other plants, produce these
double flowers. They must be grown from plant cuttings because
the plants, having lost their reproductive organs, are effectively
sterile.
In the latest
discovery, the UCSD biologists report that they found in the mustard
plant, Arabidopsis, that two of the SEP genes, in combination
with three other genes responsible for floral development, are
"sufficient to convert leaves into petals."
The three
other genes are part of a complex known to specify the development
of sepals, petals and stamens. These genes are normally not expressed
in leaves, so the task of producing plants capable of expressing
all five genes in leaves was an arduous one for the researchers.
"To do
this, we did it one at a time and then started crossing them together,
each time selecting for plants that had the additional gene introduced,"
says Yanofsky. "Each of the genes we work with is normally
active only in the flower. So we had to use genetic tricks to
turn on five different genes in leaves, where they are normally
not active.
"In all,
the crossings alone took about a year just to finally obtain plants
that expressed all five genes simultaneously in leaves. It wasn't
easy, but the result was very satisfying."
The team's
research was sponsored by grants from the National Science Foundation,
the National Institutes of Health and the U.S. Department of Agriculture.
|
