New genes for complete-protein beams.

New genes for complete-protein beans

Legumes and grains provide plenty of protein for a healthy meal, but neither alone provides a complete set of the amino acids humans (and all single-stomached animals) need to build and repair their tissues. Beans are low in the sulfur-containing amino acids methionine and cysteine; grains are low in lysine.

But genetic engineering could change that. For the first time, scientists have genetically manipulated a plant to increase its content of the essential amino acid methionine. The work was done in tobacco plants; now other scientists are seeking to develop a technique to insert the gene into legumes such as soybeans. Transgenic methionine-enriched soybeans should be available to consumers within two to three years, predicts plant molecular biologist Samuel Sun of the University of Hawaii in Honolulu, who developed the new tobacco plant with co-workers at the Plant Cell Research Institute in Dublin, Calif.

High-methionine beans would help prevent nutritional deficiencies in regions of the world where people depend on a single crop as their protein source. And in the United States, such legumes would prevent the need to supplement poultry and pig soybean feed with synthetic methionine, Sun says.

To create methionine-rich tobacco plants, Sun and his associates inserted into tobacco seeds a Brazil-nut gene coding for a protein high in methionine. The seeds grew into plants with 30 percent more methionine than control tobacco plants. The transgenic tobacco plants looked normal and contained normal amounts of other tobacco-plant proteins, Sun says.

In the 1960s, conventional breeding attempts to add lysine to corn and barley altered several proteins and resulted in textural and yield problems. Sun's genetic manipulation is more precise and less likely to result in such undesirable effects, he told SCIENCE NEWS.