Caltech discovers genetic process for controlling plant characteristics

PASADENA-Caltech biologists have harnessed a gene communication network that controls the size and shape of a flowering land plant.

The discovery is a fundamental advancement in understanding the processes that make plants what they are. The knowledge could also lead to greater control over certain characteristics of plants such as fruit size and stem durability.

In the March 19 issue of the journal Science, Professor of Biology Elliot Meyerowitz and his colleagues explain how they have managed to control three genes found in the "shoot apical meristem." This structure is the source of all cells creating a plant's leaves, stems, and flowers, and is somewhat analogous to the stem cells in animals.

The shoot apical meristem-also known as SAM-begins as a portion of the seed comprising just a few hundred cells. Like stem cells, they are undifferentiated at first, but as the young organism develops, they diversify to create the cells that make up all the recognizable features. "These divide in highly specific patterns to make leaves and stems and flowers," says Meyerowitz, who specializes in the molecular biology of plants. "Everything you see above ground arises from these cells."

Working with the nondescript flowering plant known as Arabidopsis thaliana, the Meyerowitz team first cloned the genes that gave appearance to the plant. These genes, known as CLV1 and CLV3, turned out to reveal a communication network that the plant uses to make its various parts.

Meyerowitz and his team discovered that the Arabidopsis plant tends to grow differently when the genes are disrupted. For example, the normal plant is about six inches in height with a thin, fragile stem and a few white flowers at the top.

But when the genes are knocked out, the plant grows a much thicker stem and mutant flowers with extra organs of all types, especially stamens and carpels.

In effect, this means that the researchers are in control of the genetic mechanism that governs various characteristics of a plant. And since the effect is genetic, the mutated characteristics are passed along to future generations.

Meyerowitz says the discovery could be used to mutate certain plants of human benefit so that they would have more favorable traits. For example, wheat might be altered so that the stem would be stouter and more resistant to being blown over.

But many of these effects have been accomplished for centuries with selective breeding, he says.

"The difference between a cherry tomato and a big beefsteak tomato is just like the difference between a normal Arabidopsis plant and those mutant for CLV1 or CLV3," he says. "We're not sure if it's exactly the same gene because we haven't yet looked.

"So there are ways to make fruit bigger, for example, without understanding the process," he says. "But what we're trying to do is understand the process."

Also involved in the research are Jennifer Fletcher, a research fellow in biology at Caltech; Mark Running, a graduate of Caltech who is now at UC Berkeley; Rüdiger Simon of the Institut für Entwicklungsbiologie in Cologne, Germany; and Ulrike Brand, a grad student in Simon's lab.