Genetic engineering of grain and pasture legumes for improved nutritive value

Abstract

This review describes work aimed at the improvement of the nutritive value of grain and forage legumes using gene transfer techniques. Two traits which are amenable to manipulation by genetic engineering have been identified. These are plant protein quality and lignin content. In order to increase the quality of protein provided by the legume grains peas and lupins, we are attempting to introduce into these species chimeric genes encoding a sunflower seed protein rich in the sulphur-containing amino acids methionine and cysteine. These genes are designed to be expressed only in developing seeds of transgenic host plants. Chimeric genes incorporating a similar protein-coding region, but different transcriptional controls, are being introduced into the forage legumes lucerne and subterranean clover. In this case the genes are highly expressed in the leaves of transformed plants, and modifications have been made to the sunflower seed protein-coding sequences in order to increase the stability of the resultant protein in leaf tissue. Another approach to increasing plant nutritive value is represented by attempts to reduce the content of indigestible lignin in lucerne.

Expression of a methionine-rich storage albumin from the Brazil nut (Bertholletia excelsa H.B.K., Lecythidaceae) in transgenic bean plants (Phaseolus vulgaris L., Fabaceae)

“…Increased levels of methionine in seeds of transgenic N. tabacum (30%), B. napus (11 to 33%) and A. thaliana (20%) have been reported (Altenbach et al, 1989(Altenbach et al, , 1992De Clercq et al, 1990;Guerche et al, 1990;Conceição et al, 1994;Saalbach et al, 1994;Tu et al, 1994;Pickardt et al, 1995). A methionine-rich sunflower 2S-albumin gene has been used to increase the methionine content of grain and pasture legumes (Tabe et al, 1993). We have reported the transient expression of the Brazil nut 2S-albumin gene in cells of the bean embryonic axis after transformation by particle bombardment (Aragão et al, 1992).…”

Seed storage proteins: structures and biosynthesis.

“…Most notably, Altenbach et al (1987Altenbach et al ( ,1992 have used the 2s albumin of Brazil nut, which is rich in methionine (Youle and Huang, 1981), to increase the methionine content of tobacco seeds by up to 30%, and Higgins and co-workers have used the methioninerich sunflower 2s albumin SFA8 to increase the methionine content of forage grasses (Tabe et al, 1993). In addition, the 2s albumins of Arabidopsis have been used as "hosts" for the synthesis of biologically active peptides, including the pentapeptide Leu-enkephalin (Vandekerckhove et al, 1989) and a 28-residue antibacterial peptide from Xenopus (De Clercq et al, 1990;.…”

Enhanced methionine levels and increased nutritive value of seeds of transgenic lupins ( Lupinus angustifolius L.) expressing a sunflower seed albumin gene

“…A high proportion of SSA therefore should escape conversion to microbial protein in the rumen, and thus be preserved for digestion and absorption in the lower gastrointestinal tract (9).…”