Lam, Vivienne , Chang, Ying , Rai, Hardeep , Brodribb, Tim J. , Feild, Taylor S. , Mathews, Sarah , Graham, Sean W. .
Phylogenetic placement of the parasitic and mycoheterotrophic conifer Parasitaxus usta and molecular evolution of its plastid genome.
Parasitaxus usta (Podocarpaceae) is a small coniferous shrub restricted to the New Caledonian rain forest understorey. It obtains its fixed carbon, water and other nutrients from a podocarp “host” tree (Falcatifolium taxoides) via graft-like attachments and a unique combination of mycoheterotrophy and hemiparasitism. Previous attempts to place Parasitaxus precisely in Podocarpaceae phylogeny did so with only weak to moderate support. We retrieved plastid genome regions comprising 18 genes and associated non-coding regions from exemplar species that were carefully selected to represent the broad phylogenetic backbone of Podocarpaceae, a southern hemisphere conifer family with ~ 19 genera and ~200 species. Our results provide strong support for a sister-group relationship between Parasitaxus and two monotypic genera found outside New Caledonia. The plastid genetic apparatus regions examined here (multiple ribosomal protein genes, RNA polymerase subunit genes and matK) are all open reading frames and presumably code for functional proteins. A subset of the photosynthetic genes (including multiple photosystem II subunits) have interrupted reading frames, due to accumulated indels and internal stop codons. These presumptive pseudogenes were retrieved as multiple divergent copies. They all represent recent duplications in the stem lineage of the species. A plastid ATP synthase subunit gene (atpB) is present as an open reading frame, hinting at the retention of an active PSI-mediated electron transport cycle.
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1 - University of British Columbia, UBC Botanical Garden and Centre for Plant Research, 6804 SW Marine Drive, Vancouver, BC, V6T 1Z4, Canada
2 - University of British Columbia, UBC Botanical Garden and Certre for Plant Research, 6804 SW Marine Drive, Vancouver, BC, V6T 1Z4, Canada
3 - Harvard University, Arnold Arboretum, Harvard University Herbaria, 22 Divinity Avenue, Cambridge, MA, 02138, USA
4 - University of Tasmania, Department of Plant Sciences, Hobart, Tasmania, 7001, Australia
5 - University of Tennessee, Department of Ecology and Evolutionary Biology, Knoxville, TN, 37996, USA
6 - University of British Columbia, Botanical Garden And Centre For Plant Research, 6804 Sw Marine Drive, Vancouver, British Columbia, V6T 1Z4, Canada
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Cottonwood C/Snowbird Center
Date: Wednesday, July 29th, 2009
Time: 8:30 AM