Plant protein improvement by genetic engineering: Use of synthetic genes.

摘要

The essential amino acid composition of plant foodstuffs is very important, especially in the developing countries where people very heavily depend on plant proteins from a single source. In these situations, it would be highly beneficial to 'engineer' the plant to produce proteins with a balanced essential amino acid content.;Recombinant DNA technology and Agrobacterium-based vector systems offer a novel approach to modify plant proteins. Several attempts with some encouraging results have been made to express plant storage protein genes in transgenic plants. However, improvement of the quality of plant protein using these techniques is in an early stage.;In this dissertation, the author tried to develop a system to improve the nutritional value of plant proteins using synthetic genes by utilizing the current techniques of recombinant DNA technology and Agrobacterium-based vector systems. Using a synthetic gene (HEAAE-DNA), which is 292 basepairs long and encodes a protein composed of about 80% essential amino acids, the author transformed potato plants using an A. rhizogenes vector system and tobacco plants using an A. tumefaciens vector system. Intact potato plants and tobacco plants were regenerated from hair roots infected with transformed A. rhizogenes and leaf-disks infected with transformed A. tumefaciens, respectively. Tubers from regenerated potato plants and leaves from regenerated tobacco plants were subjected to analysis for introduction and expression of this gene. Integration of the gene into the plant genome and its expression into mRNAs and HEAAE-proteins have been demonstrated in both cases using southern, northern and western analysis. Densitometric analysis of western blot data has shown that the HEAAE-proteins comprise up to 0.65% of the total plant proteins. The significant improvement of essential amino acid content of plant foodstuffs has not been achieved due to a low level of expression. However, a system has been developed to improve the nutritional value of plant foodstuffs using synthetic genes which, we hope, will eventually produce nutritionally complete plant proteins.