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Molecular analysis of a 21.1-kb fragment of wheat chloroplast DNA bearing RNA polymerase subunit (rpo) genes

Ohnishi, Y., Tajiri, H., Matsuoka, Y., Tsunewaki, K.
Genome 1999 v.42 no.6 pp. 1042-1049
Triticum aestivum, chloroplast DNA, DNA-directed RNA polymerase, genes, genetic techniques and protocols, nucleotide sequences, transfer RNA, evolution, Zea mays, Oryza sativa, amino acid sequences, genetic recombination, intergenic DNA
The entire nucleotide sequence of a 21.1-kb fragment of wheat chloroplast (ct) DNA was determined. This fragment carries 18 intact genes and parts of two additional genes, including the three RNA polymerase genes rpoB, rpoC1, and rpoC2. The gene arrangement of this region is conserved in wheat, rice, and maize, but not in non-grass species. Comparison of these 20 genes in wheat, rice, and maize showed that tRNA genes evolved more slowly than protein-coding genes in the chloroplast genome. Intergenic regions evolved much faster than both types of genes. Although the 19 genes of wheat, except for orf42, showed high identity to those of other plants, there were three novel structural features in the wheat rpoC2 gene; a deletion of 81 bp in the middle region, a variable insertion (408 bp), and a nonsense mutation in the 3' terminal region, resulting in truncation of a sequence of ca. 10 amino acids. An intermolecular recombination between the stretches of CTTAT and CTTTT was suggested as the mechanism of the 81-bp deletion in the wheat rpoC2 gene. Evolutionary distance between the chloroplast genomes of wheat and maize was larger than those between wheat and rice and between rice and maize.