July 7, 1997 Scientists at the Carnegie Institution and the University of California, Berkeley, have discovered a mutation in plants that makes the tap root accumulate large amounts of oils, proteins, and starch. The discovery could lead to genetically engineered plants that store commercially useful substances in an enlarged root. The finding could also make possible the creation of more nutritious root crops with a better balance of oil, protein, and starch. (Most root crops in Third World countries, such as cassava and taro, contain only starch.) The mutation was found in the experimental plant Arabidopsis thaliana. Once the gene containing the mutation has been cloned, it should be possible to track down the analogous gene in other plants, such as turnips, radishes, and sweet potato.
The mutation, called "pickle" because of its appearance, was discovered independently by two teams who report their findings in a joint paper in the July 4 issue of Science. The leader of the Carnegie team is Christopher Somerville, director of Carnegie's Department of Plant Biology in Stanford, California. The leader of the Berkeley team is Z. Renee Sung, professor of plant and microbial biology at UC Berkeley.
The pickle mutation mimics what happens in seeds, which typically are the major structures accumulating and storing proteins and oils. That's the reason seeds are excellent sources of these substances, and are nutritionally superior to root crops. The scientists found that the mutated plant fails to switch the tap root cells from their seed or embryonic program of storing protein and oil to the adult program. "Normally after germination the plant begins to express a new set of genes that cause the seedling to mature into an adult," says Somervillle. "In this mutation the cells destined to become primary root cells retain the character of embryonic cells. They fail to make the switch from embryonic to adult." The Carnegie team found that gibberellin, a common plant hormone required for seed germination and growth after germination, plays an important part in the switch from embryo to adult. The mutation has its greatest effect when gibberellin is not present during the first 24 hours of growth, thus establishing a hitherto unknown role for this plant hormone.
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The research was supported by an NSF grant to Sung and a US DOE grant to Somerville. Dr. Somerville can be reached at 415-325- 1521, ext. 203 or firstname.lastname@example.org; Dr. Sung is at 510-642-6966 or email@example.com.
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