GENETIC-ENGINEERING OF GRAIN AND PASTURE LEGUMES FOR IMPROVED NUTRITIVE-VALUE

This review describes work aimed at the improvement of the nutritive v alue of grain and forage legumes using gene transfer techniques. Two t raits which are amenable to manipulation by genetic engineering have b een identified. These are plant protein quality and lignin content. In order to increase the quality of protein provided by the legume grain s peas and lupins, we are attempting to introduce into these species c himeric genes encoding a sunflower seed protein rich in the sulphur-co ntaining amino acids methionine and cysteine. These genes are designed to be expressed only in developing seeds of transgenic host plants. C himeric genes incorporating a similar protein-coding region, but diffe rent transcriptional controls, are being introduced into the forage le gumes lucerne and subterranean clover. In this case the genes are high ly expressed in the leaves of transformed plants, and modifications ha ve been made to the sunflower seed protein-coding sequences in order t o increase the stability of the resultant protein in leaf tissue. Anot her approach to increasing plant nutritive value is represented by att empts to reduce the content of indigestible lignin in lucerne.