Molecular Ecology and Evolution
Stefanovic, Sasa , Kuhlman, Peter , Calie, Pat , Palmer, Jeffrey D. .
Rapid evolution of plastid RNA polymerases in three unrelated flowering plant lineages.
Transcription in plastids is dependent on the activity of two distinct RNA polymerases. The first type, termed NEP, is a single-subunit enzyme encoded by a nuclear gene. The second polymerase, termed PEP, is a bacterial-type, multi-subunit enzyme encoded by four genes in the plastid genome. The PEP is the primary transcriptional engine for expression of genes involved in photosynthesis and is regulated by interactions with sigma factors and perhaps as many as ten additional transcription factors that confer sensitivity to redox state and other organellar environmental cues. As is to be expected for an indispensable enzyme with multiple interaction partners, the rpo genes encoding the PEP subunits normally evolve at a conservative rate with a ratio of synonymous to non-synonymous substitutions that suggests strong purifying selection. Remarkably, a Southern blot survey of over 280 diverse angiosperm species has uncovered three independent lineages of fully photosynthetically capable flowering plants for which this is not the case. In the rpo genes of species of Annona (Annonaceae), Passiflora (Passifloraceae), and Pelargonium (Geraniaceae), there is evidence for gene- and lineage-restricted acceleration of non-synonymous substitutions leading to extremely divergent PEP amino acid sequences. Despite the extremity of sequence change, conservation of sequence motifs associated with RNA polymerase function suggests that the rapidly-evolving rpo genes are capable of encoding functional polymerases. RT-PCR data are also consistent with the interpretation that these genes are functional, raising intriguing questions about why three disparate lineages of plants would be experiencing positive selection for dramatically altered PEP enzymes.
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1 - University of Toronto at Mississauga, Biology, 3359 Mississauga Rd N, Mississauga, Ontario, L5L1C6, Canada
2 - Denison University, Department of Chemistry and Biochemistry, Granville, Ohio, 43023, USA
3 - Eastern Kentucky University, Department of Biological Sciences, Moore 235, 525 Lancaster Avenue, Richmond, Kentucky, 40475, USA
4 - Indiana University, Department of Biology, Jordan Hall, 1001 East Third Street, Bloomington, Indiana, 47405, USA
plastid RNA polymerase
Presentation Type: Oral Paper:Papers for Topics
Location: Boulevard B/Hilton
Date: Wednesday, July 11th, 2007
Time: 11:30 AM