The complete nucleotide sequence of the mitochondrial genome of sugar beet (<em>Beta vulgaris</em> L.) reveals a novel gene for tRNA<sup>Cys</sup>(GCA)
We determined the complete nucleotide sequence of the mitochondrial genome of an angiosperm, sugar beet (Beta vulgaris cv TK81-O). The 368 799 bp genome contains 29 protein, five rRNA and 25 tRNA genes, most of which are also shared by the mitochondrial genome of Arabidopsis thaliana, the only other completely sequenced angiosperm mitochondrial genome. However, four genes identified here (namely rps13, trnF-GAA, ccb577 and trnC2-GCA) are missing in Arabidopsis mitochondria. In addition, four genes found in Arabidopsis (ccb228, rpl2, rpl16 and trnY2-GUA) are entirely absent in sugar beet or present only in severely truncated form. Introns, duplicated sequences, additional reading frames and inserted foreign sequences (chloroplast, nuclear and plasmid DNA sequences) contribute significantly to the overall size of the sugar beet mitochondrial genome. Nevertheless, 55.6% of the genome has no obvious features of information. We identified a novel tRNA gene (trnC2-GCA) which shows no sequence homology with any tRNA genes reported so far in higher plants. Intriguingly, this tRNA gene is actually transcribed into a mature tRNA, whereas the native tRNA gene (trnC1-GCA) is most likely a pseudogene.
*, trans-splicing; +, present; ψ, pseudogene; ψ?, likely pseudogene; –, absent; a, three copies; b, four copies; c, two copies.
We wish to thank Drs S. Tabata, T. Kaneko, Y. Nakamura and K. Akashi for valuable discussions and suggestions, Dr T. Tsudzuki for figure drawing and Drs Y. Kishima and Y. Nishita for technical advice and continuous encouragement. This work was done in part at the Research Center for Molecular Genetics, Hokkaido University, and was supported in part by Grants in Aid for Scientific Research from the Ministry of Education, Science and Culture, Japan, and a grant from the Program for Promotion of Basic Research Activities for Innovative Biosciences, Japan. A.E. is the recipient of a Japanese Government (Monbusho) Scholarship.
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