The dynamic aspect of genome structures in plants

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Dynamic aspects of plant genomes were analyzed in the molecular level. The structure and organization of chloroplast DNA from Oryza species have been studied, and deletions which were the result of intramolecular recombination mediated by short direct-repeat sequences were found. This type of variation existed within a single species. It has been known that the mitochondrial genome of higher plant is largest and most complex among those of eukaryotes. The complexity of the genome is enhanced by the existence of chloroplast sequences in the genome. The entire set of transferred chloroplast DNA sequences in the mitochondrial genome from rice was identified and sequenced. Sixteen chloroplast sequences, ranging from 32 bases to 6.8 kb in length, were found to be dispersed throughout the rice mitochondrial genome. The transfers of segments of chloroplast DNA seem to have occurred at different times, both before the divergence of rice and maize and after this divergence. Small repeated sequences (from 60 to 66 basepairs in length)have been identified in the mitochondrial genome of rice. There are atleast ten copies of these sequences and thety are distributed throughout the mitochondrial genome. Each is potentially capable of forming a stem-and-loop structure and have been designated PRS(Palindromic Repeated Sequences). It was found that homologous recombinatio mediated by two PRSs occurred in the mtDNA of Oryza after divergence of the BB genome-type and the other genome-types of Oryza.The origins and the phylogenetic relationships between diploid and polyploid wheats have studied using molecular genetic methods. The results show the evolution of the genome mainly depends on changes in the untranslated regions of the DNA,and the evolutional rates of coding sequences are low.