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A DNA-polymerase-related reading frame (pol-r) in the mtDNA of Secale cereale
1Institut für Botanik, Westfälische Wilhelms-Universität, Münster, Germany.
Abstract:
Mitochondrial (mt)DNA of Secale cereale contains an open reading frame (pol-r), the potential translation product of which shows significant homology to the type-B DNA polymerase encoded by the S1 plasmid of Zea mays; it contains the highly-conserved domains IIa to V of family B polymerases. The pol-r ORF is transcribed, as proven by RT-PCR, but the transcript is not edited. Upstream of the putative start codon a potential promoter motif was detected, fitting well into the postulated consensus sequence of the transcription initiation regions of Z. mays and Triticum aestivum. The pol-r ORF occurs in mtDNA of the fertile rye variety "Halo" and the cytoplasmic male-sterile (CMS) line "Pampa". Both ORFs are almost identical, apart from the 3' terminus; pol-r from Halo can code for 289 amino acids, pol-r from Pampa for 312 amino acids. Based on codon usage and the lack of editing, pol-r is considered to be a "young" gene, probably introduced in the mtDNA of rye by recombination with an mt plasmid.
Insights
Mitochondrial DNA in rye (Secale cereale) features a novel gene, pol-r, homologous to a maize DNA polymerase. This gene is transcribed but not edited, suggesting its recent acquisition.
Area of Science:
- Plant Molecular Biology
- Mitochondrial Genetics
- Gene Evolution
Background:
- Mitochondrial DNA (mtDNA) harbors genes crucial for plant function.
- Plant mitochondrial genomes are dynamic, undergoing rearrangements and horizontal gene transfer.
- Understanding novel mtDNA-encoded proteins is key to deciphering mitochondrial function and evolution.
Purpose of the Study:
- To characterize a novel open reading frame (ORF) designated pol-r in Secale cereale mtDNA.
- To investigate the transcription and potential function of the pol-r gene.
- To explore the evolutionary origin of the pol-r gene in rye.
Main Methods:
- Sequence analysis of rye mtDNA to identify ORFs.
- Reverse transcription polymerase chain reaction (RT-PCR) to confirm transcription.
- Bioinformatic analysis to assess homology and identify regulatory elements.
- Comparison of pol-r sequences between fertile and cytoplasmic male-sterile (CMS) lines.
Main Results:
- Identified a pol-r ORF in Secale cereale mtDNA with homology to Zea mays type-B DNA polymerase.
- Confirmed pol-r transcription via RT-PCR; the transcript is unedited.
- Detected a potential promoter motif upstream of the pol-r start codon.
- Observed minor differences in the 3' terminus and length between pol-r in fertile and CMS rye lines.
Conclusions:
- The pol-r gene is likely a recently acquired "young" gene in rye mtDNA, possibly via plasmid recombination.
- Its homology to DNA polymerases suggests a role in mitochondrial DNA replication or repair.
- The lack of editing and presence of a promoter indicate active regulation.
- Pol-r variation between fertile and CMS lines may hint at its involvement in cytoplasmic male sterility.