Stable Expression of the Sulphur-rich 2S Albumin Gene in Transgenic Vicia narbonensis Increases the Methionine Content of Seeds

Abstract

Summary Both the narbon bean ( Vicia narbonensis ) and tobacco plants were transformed using Agrobacterium tumefaciens strains containing binary vectors with the gene coding for the methionine-rich 2S albumin of Brazil nuts under the control of either the Cauliflower Mosaic Virus 35S promoter or the legumin B4 promoter from V. faba . Stable integration in the genome was verified by both Southern blotting and segregation analysis. Under the control of the viral promoter, 2S albumin was produced in a variety of tissues at a relatively low level in both species. The LeB4 promoter conferred seed-specific high level expression in V. narbonensis and low level seed-specific expression in tobacco. A total of 50 independent transgenic narbon bean lines containing the LeB4-2S albumin construct have so far been isolated. Eighteen of these lines were further characterised and several stable homozygous lines established. Comparisons of homozygous and heterozygous progeny in these strains revealed that a doubling of the number of genes resulted in an approximate doubling in the amount of gene product. The absolute protein levels reached varied between lines. Amino acid analysis revealed an approximate 3 fold increase in the methionine content of seed protein in one R 0 line. Further analysis of these lines is aimed at determining how to achieve high level production of foreign proteins in seeds and more specifically at improving the nutritional quality of the seed protein of legumes.