The Co-expression Of Thaumatin,PDI In Maize And The Expression Of Thaumatin CDNA Gene In Yeast

Thaumatin is an extreme sweet protein, which was produced by the plant Thaumatococcus daniellii Benth. It is 3,000 times sweeter than sucrose on weight basis. Because of its low calories, high sweetness and innocuity, it has been approved for human consumption, and is currently used in products such as chewing gum, dairy produce and pharmaceuticals. It also is a potential sweet additive, which can substitute for sucrose. However, Thaumatococcus daniellii Benth can't seed outside its producing area. But gene engineering can solve this problem.Up to the present, the thaumatin gene has been expressing in many kinds of bacteria and fungi. But the product is either too little or not active. As Thaumatin comes from high plant, researchers thinked it would be better expressing in plant cells. M, Witty transfer the thaumatin gene into tomato by hairy root transformation technique in 1990. Then, he gained the transgenic plant, which is entirely sweet. However, no anther kinds of plants, which contain the thaumatin gene, are sweet. Generally, the thaumatin gene can transcript into mRNA correctly in heterogenous high plant cells. However, it is difficult to translate into the active protein. Several experimentations showed that the PDI(protein disulfide isomerase) played an important role when the protein forming high structure and secreting. Moralejo made the PDI and thaumatin gene express together in black Aspergillus, the yield of recombinant Thaumatin is 150mg/L.As a result, I expect the thaumatin gene and the PDI gene can express together in maize. After successful constructing of the botanic expressing vector pCAMBIA1302-tha-PDI, which contained of the thaumatin gene and PDI gene, the recombinant plasmid was transformed into the juvenile embryo proper of maize via agrobacterium LBA4404. We expect the thaumatin gene can express the protein successfully in maize by the tissue culture technique of juvenile embryo proper induction. To our pity, the juvenile embryo proper of maize could not be brought up to be the state of differentiation. That was to say, the tissue of maize could not be a plantwith the thaumatin gene and PDI gene. So we must study and analyse the reason of the difficulty, especially by the tissue culture technique.In the experiment, we learned many methods and fished for more new technique via the juvenile embryo proper regeneration. The result was not gratifying, but we still studied a lot of ways and obtained much experience. We wish we can make great progress on this question in the future. Consequently we can contribute for the people's life.