Flower Pattern Switch Found By Salk Scientists

July 22, 1999

Flower Pattern Switch Found By Salk Scientists

July 22, 1999

La Jolla, CA – During the turbulent ’60s, the phrases “flower power” and “petal power” were counterculture slogans that invoked peace and love. Though science has yet to design flowers capable of fulfilling the wishes of a bygone era, researchers at The Salk Institute are learning more about the genetic power behind flower formation that one day could yield designer blooms.

Aside from the potential benefits to lovers and horticulturalists alike, the work could also result in “sneeze-free” pollenless flowers, offering a little peace to allergy sufferers as well.

In the current issue of the journal Science, Salk Associate Professor Detlef Weigel and his team report the identification of a critical link in the genetic chain of command that produces flowers and some of the key components specifying their reproductive organs – the male reproductive organs, the stamens, and the female reproductive structures, the carpels.

“Flowers have certain features – a particular number of floral organs and organ types, for instance four petals – and each organ type is defined by the activity of a certain combination of regulatory genes,” said Maximilian A. Busch, a postdoctoral fellow in the Weigel laboratory and co-first author of the study.

“We’ve found the switch for one of these genes, which is necessary to specify stamens and carpels, ” he continued. “It’s the first known connection between the signals that tell a plant to make a flower and those that specify what the flower will look like.”

The study builds on earlier work from Weigel’s group that identified the LEAFY gene, a “master switch” for flower development. Salk investigators had shown that LEAFY was itself sufficient to trigger flower formation, a finding with a plethora of potential agricultural applications, including accelerating flower and fruit production in crop plants and collapsing the breeding cycles for trees to spans amenable to experimental manipulation.

But the targets for LEAFY remained at large until the current study.

“It stood to reason that LEAFY would activate the so-called ABC genes, patterning genes that were known to be turned on in different structures of the flower,” said Busch. “And now we have the first direct evidence that LEAFY attaches to these genes and switches them on.”

The patterning genes “instruct” different parts of a flower to develop into sepals, petals, stamens or carpels. The “A” genes are active in the outer parts of the flower, the sepals and petals; the “C” genes specify the inner sections, the reproductive structures; and the “B” genes overlap.

The current study shows that LEAFY activates a gene called AGAMOUS, a member of the “C” family, and investigators expect that other ABC genes will also have switches controlled by LEAFY. Having all the signals in hand should allow for the engineering of flowers with particular desired features.

“For example,” said Weigel, “we know that plants missing the AGAMOUS gene don’t make any reproductive organs. Instead the A genes take over the whole flower, producing many extra petals, a spectacular effect that horticulturists find appealing. Knowing all the cues that lend a flower its size and shape should permit the deliberate design of flowers through genetic manipulations. For example, the selective removal of stamens would eliminate pollen, a common allergen.”

Thus, bringing to the garden prettier posies and sneeze-free sniffs.

Co-first author Kirsten Bomblies is a research assistant in Weigel’s laboratory. The study, titled “Activation of a floral homeotic gene in Arabidopsis,” was supported by the National Science Foundation and the Department of Energy. Busch was the recipient of a fellowship from the Human Frontier Science Program Organization.

The Salk Institute for Biological Studies, located in La Jolla, Calif., is an independent nonprofit institution dedicated to fundamental discoveries in the life sciences, the improvement of human health and conditions, and the training of future generations of researchers. The Institute was founded in 1960 by Jonas Salk, M.D., with a gift of land from the City of San Diego and the financial support of the March of Dimes Birth Defects Foundation.