Abstract Detail

Systematics Section/ASPT

Straub, Shannon [1], Cronn, Richard [2], Edwards, Christopher [1], Fishbein, Mark [3], Liston, Aaron [1].

Horizontal transfer of DNA from the mitochondrial to the plastid genome in milkweeds (Apocynaceae).

Plant plastomes are highly conserved and have generally been regarded as impervious to horizontal gene transfer (HGT). Sequencing of the 158 kb plastome and the 690 kb mitochondrial genomes of Asclepias syriaca L. (Apocynaceae) revealed evidence of intracellular HGT of a 2.4 kb segment of DNA, including an rpl2 pseudogene, from the mitochondrial genome to the rps2-rpoC2 intergenic spacer region of the plastome. The region transferred to the plastome is flanked by chloroplast sequence (5’ rps2-rpoC2 intergenic spacer and 3’ rpoC2) in the mitochondrial genome. In plants, HGT from the plastome to the mitochondrial genome is common, and likely provided the mechanism for this rare HGT back to the plastome through homologous recombination. Twenty-two other species of Apocynaceae were surveyed with PCR for evidence of the plastome insertion and presence of the mitochondrial 3’ rpoC2 pseudogene, and whole plastomes were sequenced for eleven species. Analyses of these data showed that the insertion, which averages 4.5 kb in the other species, is restricted to, and thus a synapomorphy for, Asclepiadeae. The results also indicated that the transfer of the 3’ rpoC2 pseudogene predates the HGT to the plastome, supporting homologous recombination as the mechanism. Phylogenetic analysis of the plastome sequences also resolved the phylogeny of Asclepiadoideae and supported Eustegia (L.f.) N.E.Br., an enigmatic monotypic African genus, as sister to the rest of Asclepiadeae. Although the plastome insertion has been maintained over a long evolutionary time period, likely since the late Eocene, sequencing of the chloroplast transcriptome did not show expression of this region, suggesting a lack of current function. This is only the second report of HGT from a plant mitochondrial genome to the plastome among the more than 250 land plant plastomes that have been sequenced, indicating that this type of HGT is indeed rare.

Broader Impacts:

1 - Oregon State University, Department of Botany & Plant Pathology, 2082 Cordley Hall, Corvallis, OR, 97331-2902, USA
2 - USDA Forest Service, 3200 SW Jefferson Way, Corvallis, OR, 97330, USA
3 - Oklahoma State University, 301 Physical Sciences, Stillwater, OK, 74078, United States

Keywords:
horizontal gene transfer
Apocynaceae
Asclepias
plastome
mitochondrial genome.

Presentation Type: Oral Paper:Papers for Sections
Session: 13
Location: Rosedown/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 3:00 PM
Number: 13007
Abstract ID:770
Candidate for Awards:George R. Cooley Award