Genes in one part of a plant can override the genetic program in a distant part of the same plant and change how the plant grows, according to researchers at the University of California, Davis.

"This forces us to look at plant growth and development a little differently," said UC Davis plant biologist Neelima Sinha, who supervised the research team. The system could act like the hormonal system or nervous system in animals, taking orders from one part of the organism to another. For example, environmental signals might switch on genes in the leaves of a plant. Messenger RNA made from these genes would travel to other parts of the plant and change how it grows.

Short pieces of messenger RNA are the blueprints for making proteins from genes encoded by DNA. Conventionally, the process of transcription from DNA to RNA and then translation from RNA to protein is supposed to take place within the same cell.

However, scientists have found that messenger RNA moves throughout plants using a network of tubes called the phloem, said Sinha.

Biologists did not know whether this long-distance movement of messenger RNA had a real function in plants.

Sinha's team grafted shoots from normal tomato plants onto tomato plants with a genetic change that causes abnormally shaped leaves. They found that new leaves on the normal part of the plant began to develop the abnormal leaf pattern.

When they looked at cells from the plants, they found that RNA specific to the genetic change had traveled from the abnormal leaves to the normal part of the plant. The RNA accumulated in the meristems -- the growing tips of the shoots.

"This is the first study to show that long-distance transported RNA is functional," said graduate student Minsung Kim, who is lead author on the study. Because the RNA accumulated in cells of the meristem, it must carry within it an address to take it to that location.

The study is published in the July 13 issue of the journal Science. The other authors on the paper are graduate student Sharon Kessler and undergraduate student Wynnelena Canio.

Editor's note: Electronic images of the grafted tomato plants are available. Contact the News Service for details.