Article

Insights into the evolution of mitochondrial genome size from complete sequences of Citrullus lanatus and Cucurbita pepo (Cucurbitaceae).

Department of Biology, Indiana University, USA.
Molecular Biology and Evolution (impact factor: 5.55). 06/2010; 27(6):1436-48. DOI:10.1093/molbev/msq029 pp.1436-48
Source: PubMed

ABSTRACT The mitochondrial genomes of seed plants are unusually large and vary in size by at least an order of magnitude. Much of this variation occurs within a single family, the Cucurbitaceae, whose genomes range from an estimated 390 to 2,900 kb in size. We sequenced the mitochondrial genomes of Citrullus lanatus (watermelon: 379,236 nt) and Cucurbita pepo (zucchini: 982,833 nt)--the two smallest characterized cucurbit mitochondrial genomes--and determined their RNA editing content. The relatively compact Citrullus mitochondrial genome actually contains more and longer genes and introns, longer segmental duplications, and more discernibly nuclear-derived DNA. The large size of the Cucurbita mitochondrial genome reflects the accumulation of unprecedented amounts of both chloroplast sequences (>113 kb) and short repeated sequences (>370 kb). A low mutation rate has been hypothesized to underlie increases in both genome size and RNA editing frequency in plant mitochondria. However, despite its much larger genome, Cucurbita has a significantly higher synonymous substitution rate (and presumably mutation rate) than Citrullus but comparable levels of RNA editing. The evolution of mutation rate, genome size, and RNA editing are apparently decoupled in Cucurbitaceae, reflecting either simple stochastic variation or governance by different factors.

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Keywords

Citrullus lanatus
 
compact Citrullus mitochondrial genome
 
Cucurbita mitochondrial genome
 
Cucurbita pepo
 
Cucurbitaceae
 
discernibly nuclear-derived DNA
 
genome size
 
genomes range
 
higher synonymous substitution rate
 
larger genome
 
low mutation rate
 
mitochondrial genomes
 
mutation rate
 
plant mitochondria
 
RNA editing content
 
RNA editing frequency
 
seed plants
 
simple stochastic variation
 
single family
 
unprecedented amounts