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Plant Physiology Preview Published on April 7, 2006; 10.1104/pp.105.075564
Received December 14, 2005 Promoter Shuffling at a Nuclear Gene for Mitochondrial RPL27: Involvement of Inter- and Subsequent Intrachromosome Recombinations
Genetic Diversity Department, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki 305-8602, Japan; Laboratory of Plant Molecular Genetics, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657 Japan * Corresponding author; email: kadowaki{at}affrc.go.jp.
The Reclinomonas americana mitochondrial genome contains an rpl27 gene, whereas the rpl27 gene is absent from all plant mitochondrial genomes examined to date. This suggests that plant mitochondrial rpl27 genes have been transferred previously from the mitochondrial genome to the nuclear genome. A nuclear cDNA encoding mitochondrial RPL27 (rpl27) was identified in rice (Oryza sativa). Three similar sequences were identified: rpl27-1 and rpl27-2 on chromosome 8 and rpl27-3 on chromosome 4. Harr plot analysis suggests that they were generated by inter- and intrachromosomal duplications. Interestingly, the transcribed rpl27 gene (rpl27-1) acquired a promoter sequence that was derived from the rice spt16 (Osspt16) gene, the homolog of a global transcription factor in yeast (Saccharomyces cerevisiae) located downstream from the rpl27-3 sequence on chromosome 4, after inter- and intrachromosomal recombination. Reverse transcription PCR and promoter assay revealed that the rpl27 mRNAs were mainly transcribed from rpl27-1. A repeat of seven nucleotides (AATAGTT) was identified at the junction of rpl27-1 and rpl27-2 on chromosome 8, and the same repeat was also identified at the 5 end of rpl27-2 and the 3 end of rpl27-1. This repeat (AATAGTT) contains the hot-spot sequence AGTT, which is preferentially recognized by topoisomerase I in wheat (Triticum aestivum) germ, suggesting the involvement of topoisomerase I in this recombination. We here report the example of promoter shuffling and show that this promoter shuffling resulted from a recent segmental duplication through inter- and intrachromosomal recombination events.
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