A soybean vegetative storage protein accumulates to high levels in various organs of transgenic tobacco plants

Soybean vegetative storage proteins (S-VSPs) are a group of high-lysine proteins. These proteins can accumulate up to 15% of the soluble leaf proteins in young shoots, as well as in shoots of depodded mature plants. Closely related proteins are found in forage crops, such as alfalfa. We have expressed the S-VSP alpha gene, fused to the strong constitutive cauliflower mosaic virus 35S promoter, in transgenic tobacco as a model plant to study the potential of producing high levels of S-VSPs for the nutritional improvement of forage crops. S-VSP alpha was detected in the soluble (albumin) fraction of the transgenic plants. The transgenic protein migrated in sodium dodecyl sulfate-polyacrylamide gel electrophoresis similarly to the natural S-VSP alpha of soybean, suggesting that it was correctly processed in tobacco and accumulated in the vacuoles, The S-VSP alpha ranged between 2 and 6% of the soluble proteins in leaves of the transgenic plants and was present in various organs and in mature leaves. Our results suggest that S-VSPs can serve as an excellent protein source for improving the nutritional quality of crop plants, particularly cereal forage and grains, which contain limiting levels of lysine. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.