Turning Leaves into Petals

Through a remarkable sleight of gene, scientists at the University of California at San Diego and the National Autonomous University of Mexico have tricked leaves into forming petals instead. In practice, the results mean that you might soon be able to buy roses sporting soft petals all the way up the stem.

"This is a very exciting discovery," says Martin F. Yanofsky of UCSD. "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 that we were missing a piece of the puzzle, and now we know exactly what we were missing."

A typical flower consists of four rings, or whorls. The outer whorl is made up of sepals, which surround a bud before it opens; next comes a ring of petals; inside the petals are the stamens, the male reproductive organs; and in the very center are carpels, or female parts. More than 200 years ago, biologists first suggested that the whorls were, in essence, modified leaves. But no one could figure out how to isolate the genes involved.

Last May, Yanofsky and his colleagues discovered a trio of genes that, when modified together, produced so-called double flowersblooms in which the petals, stamens and carpels all became sepals. Building on that work, they have now found that modifying two of these SEP genes in concert with three other flower development genes makes leaves turn into petals. In the image above, the Arabidopsis plant on the left has four of these five genes switched on; all five genes are expressed in the plant on the right.