Cloning And Regulation Of Genes Involved In Tomato Ascorbic Acid Biosynthesis And Metabolism

L-ascorbic acid (AsA), also named vitamin C, has a multitude of functions in organisms. AsA is an essential component of human nutrition, but humans lack the ability to synthesize AsA as a result of a mutation in the last enzyme required for AsA biosynthesis. AsA, therefore, must be acquired regularly from dietary sources, primarily from plants rich in AsA. AsA is involved in the process of cell division, cell expansion and plant growth. AsA also plays an important role as an antioxidant and protects the plant during oxidative damage by scavenging free radicals and reactive oxygen species that are generated during photosynthesis, oxidative metabolism and various stresses. By regulating the expression of genes involved in plant ascorbic acid biosynthesis and metabolism, it is possible to increase the AsA contents of plants, thus improve the nutritive values of plant foods and the resistance to environmental stresses.Tomato is a worldwide vegetable with high nutritive values. However, most genes involved in tomato ascorbic acid biosynthesis and metabolism have not been cloned and there are nearly no reports about the gene regulation. Therefore, this study aims to clone and regulate the expression of genes involved in tomato AsA biosynthesis and metabolism and expects to obtain tomato materials with high content of AsA by transgenic techniques. The main results were as follows:1. The full-length cDNA of GDP-D-mannose pyrophosphorylase (GMP, EC 2.7.7.22), which catalyzes the formation of GDP-D-mannose, was cloned by RACE-PCR and the sequence data have been submitted to the DDBJ/EMBL/GenBank databases under accession number AY605668. The full-length of GMP cDNA is 1535 bp and contains a complete open reading frame (ORF) of 1086 bp, which encoding 361 amino acids (aa). Homology analysis of tomato GMP showed high homology with GMP from other plants. The full-length cDNA of L-galactono-1,4-lactone dehydrogenase (GLDH, EC 1.3.2.3), which is the last key enzyme of plant ascorbic acid biosynthesis, was cloned by RT-PCR based on the published sequence (AB080690). The complete ORF of GLDH...