Extensive loss of translational genes in the structurally dynamic mitochondrial genome of the angiosperm Silene latifolia

Sloan D.B., Alverson A.J., Štorchová H., Palmer J.D., Taylor D.R

Keywords: Mitochondrial genome, Silene latifolia, gene loss
Abstract: Mitochondrial gene loss and functional transfer to the nucleus is an ongoing process in plants, resulting in substantial variation across species in mitochondrial gene content. The Caryophyllaceae represents one lineage that has experienced a particularly high rate of mitochondrial gene loss relative to other angiosperms. In this study, we report the first complete mitochondrial genome sequence from a member of this family, Silene latifolia. The genome can be mapped as a 253,413 bp circle, but its structure is complicated by a single repeated region that is present in 6 copies. Active recombination among these copies produces a suite of alternative genome configurations that appear to be at or near “recombinational equilibrium”. The genome contains fewer genes than any angiosperm mitochondrial genome sequenced to date, with putatively functional copies for only 26 of the 41 protein genes inferred to be present in the ancestor of all angiosperms. Five additional protein genes are present as apparent pseudogenes. As observed more broadly in angiosperms, ribosomal proteins have been especially prone to gene loss in the S. latifolia lineage. The genome has also experienced an unprecedented reduction in tRNA content. Although S. latifolia retains copies of all 3 mitochondrial rRNA genes, these genes exhibit an accelerated substitution rate relative to other plants. In particular the 5S rRNA (rrn5) gene sequence is highly divergent. These results provide insight into broader genomic changes that may be associated with the well-documented pattern of protein gene loss in angiosperm mitochondrial genomes.
IEB authors: Helena Štorchová