Studies on the molecular breeding model by expression vectors

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Chloroplast and mitochondrial genomes code for important genes for agriculture. However, since they are inherited maternally in most cases, it is difficult to improve these genomes by ordinally breeding methods. New breedings based on the molecular biology are expected to help programs to improve these genomes. As a model of the molecular breeding, we have conducted the analysis of molecular structures of chloroplast and mitochondrial genomes in rice.1.Structure of chloroplast DNA from Oryza sativa A physical map and an overlapping clone bank of the ctDNA were constructed. Nucleotide sequences of genes which are important for photosynthesis, rbcL, atpB/E and psbA, were determined. The expression of these genes were also studied by S_1 mapping, primer extension and Northern analysis.2.Complete nucleotide sequence of the ctDNA Using our clone bank, the complete nucleotide sequence of the ctDNA was determined. It is a circular and 134,525 bases long. All genes existed in tobacco ctDNA were also found in rice.3.Cloning of ctDNA from wild species in the genus Oryza Chloroplast DNAs were isolated from Oryza australiensis O. punctata and O.officinalis, and fragments were cloned into lambda DNA. A physical map and an overlapping clone bank of each DNA were constructed.4.Structure of mitochondrial DNA from oryza sativa Mitochondrial DNA was isolated from green leaves of Oryza sativa, and fragments were cloned into lambda DNA. A genetic and physical map of the DNA was constructed by "genome walking". The size of the master circle of mtDNA from rice is 528 kb. The DNA contain many fragments homologous to ctDNA fragments.