CHARACTERIZATION OF THE RADISH MITOCHONDRIAL NAD3 RPS12 LOCUS - ANALYSIS OF RECOMBINATION REPEATS AND RNA EDITING/

In order to further investigate sequences that are responsible for low -frequency recombination in plant mitochondrial DNAs and RNA editing i n radish mitochondria, the nad3/rps12 locus has been isolated and char acterized from a normal cultivar of radish and the male-sterile Ogura cytoplasm. A repeated sequence that has been implicated in other radis h mitochondrial DNA rearrangements was identified at the breakpoint be tween the two loci indicating that it was also involved in the nad3/rp s12 rearrangement. Similar to some other radish mitochondrial genes, n ad3/rps12 genomic sequences already contain several, but not all, of t he bases that are typically edited in plant mitochondrial nad3 and rps 12 genes. Analysis of nad3/rps12 cDNAs indicated that the mRNAs are no t edited. One partially edited transcript was identified out of the tw enty two that were examined. This finding, along with the observation that nad3/rps12 RNAs are present at very low levels, raises the possib ility that radish mitochondria may not encode functional copies of the se genes. Consistent with this hypothesis, DNA-blot analysis detects n an3/rps12 sequences in the nucleus.