Recent Topics Posters
Dutton, Ashley , Raubeson, Linda A. .
More evidence that mutation rate in the chloroplast genome depends on copy number.
The conservative nature of the chloroplast genome's inverted repeat (IR) region is well established; however the basis for the lower mutation rate has been debated. Two ideas have been proposed to explain the reduced rate: 1) genes that, by chance, occur in the region (i.e., the rRNA genes) are slow to evolve; or 2) the presence of two copies leads to a reduced rate via copy correction. Perry and Wolfe [2002, J Mol Evol 55:501-8] explored this question in four legume plastomes. From the increased synonymous substitution rate for IR genes present once (due to IR loss) compared to those present twice (when both copies of the IR are retained), Perry and Wolfe concluded that copy number was responsible for the reduced rate in the IR region when duplicated. To investigate this phenomenon more broadly we examined mutation rate in twenty introns (some duplicated when the IR is present and some always single copy - SC) from genomes with one or two copies of IR sequence, using six legumes (three with and three without the IR duplication), seven conifers (lacking an IR duplication), six other gymnosperms (retaining an IR), and Dioon edule, the only cycad currently known to exhibit IR loss. Using intron sequences reduces the effect of functional constraints, as introns lack the same degree of selective pressure exhibited by exons, so that intron mutation rate may be more clearly influenced by copy number. We calculated and compared average distances and applied Tajima’s relative rate test separately to data sets of IR and SC introns from IR-containing and IR-less genomes. The results of both methods provide additional support for the conclusion that reduced IR mutation rate is due to copy correction between duplicated sequences.
Log in to add this item to your schedule
1 - Central Washington University, Department of Biological Sciences, 400 E University Way, Ellensburg, WA, 98926-7537, USA
Presentation Type: Recent Topics Poster
Location: Ball Room & Party Room/SUB
Date: Monday, July 28th, 2008
Time: 12:30 PM