Scientists manipulate a developmental mechanism in plants to stop them from growing stalks.

In a case of Greek mythology gone green, scientists in California have created a double-tailed plant: a mutant with a second root where its stalk would typically reside. 

Researchers at the Salk Institute for Biological Sciences in San Diego grew the mutant in order to study how the fate of a plant is determined in its embryonic stages; their findings could be used for developing agricultural plants with more desirable traits. 

“Considering a huge proportion of what we eat are actually plants, it’s important to understand how plants make roots and shoots, leaves and flowers,” said Jeff Long, an assistant professor in the department of plant cellular and molecular biology at Salk and lead author of the study, which was published in the June 9th issue of Science.

The scientists determined that a variant of the gene known as TOPLESS can cause the development of a root instead of a shoot during the development of the plant Arabidopsis thaliana, resulting in a young plant with roots at both ends. Arabidopsis is a wild mustard plant, widely used as a model organism in plant genetics. It was also the first flowering plant to have its genome sequenced. 

Scientists previously thought that the division of plants into root and shoot regions was regulated by transcription factors—proteins that directly bind to DNA and activate genes. But it turns out that the division happens as a result of a different class of proteins, called repressors, which bind transcription factors and disrupt gene activation. 

Normally, the TOPLESS gene codes for one of these repressor proteins, which inactivates the genes that cause root development in the shoot area of the plant. But when the TOPLESS gene is deactivated through mutation, root-producing genes are activated, and the fate of the top half of the plant cell goes from shoot to root. 

“Repression is probably as important, if not more important, as activation,” said John Bowman, a plant biology professor at the University of California, Davis. “It’s probably just as important, or more important, to turn off sets of genes and keep them off.”

Surprisingly, this mechanism of gene regulation in the development of body structure is almost exactly the same as in animals, Long said.

“If plants and animals actually did arise from a single-celled organism millions of years ago and broke off into different evolutionary pathways, both the animal line and the plant line inherited a common set of basic genes,” he said. “So it just turned out that in evolution, the way things developed into multicellular organisms, the same kinds of genes were used for these similar processes.”

Understanding these mechanisms at a molecular level can help us adjust the behavior of agricultural plants, Long noted. If scientists can identify genes that determine certain traits—such as kernel size in corn—they can better engineer plants to have more desirable traits. 

Arabidopsis belongs to the family of cabbages and turnips, and we eat those all the time,” Long said. “We can go back and look at those genes in our domesticated crops and see what kinds of genes were selected for to improve yield in the future.”

Originally published June 15, 2006

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