title: Whole genome duplication in coast redwood (Sequoia sempervirens) and its implications for explaining the rarity of polyploidy in conifers.
abstract: Polyploidy is common and an important evolutionary factor in most land plant lineages, but it is rare in gymnosperms. Coast redwood (Sequoia sempervirens) is one of just two polyploid conifer species and the only hexaploid. Evidence from fossil guard cell size suggests that polyploidy in Sequoia dates to the Eocene. Numerous hypotheses about the mechanism of polyploidy and parental genome donors have been proposed, based primarily on morphological and cytological data, but it remains unclear how Sequoia became polyploid and why this lineage overcame an apparent gymnosperm barrier to whole-genome duplication (WGD). We sequenced transcriptomes and used phylogenetic inference, Bayesian concordance analysis and paralog age distributions to resolve relationships among gene copies in hexaploid coast redwood and close relatives. Our data show that hexaploidy in coast redwood is best explained by autopolyploidy or, if there was allopolyploidy, it happened within the Californian redwood clade. We found that duplicate genes have more similar sequences than expected, given the age of the inferred polyploidization. Conflict between molecular and fossil estimates of WGD can be explained if diploidization occurred very slowly following polyploidization. We extrapolate from this to suggest that the rarity of polyploidy in gymnosperms may be due to slow diploidization in this clade.
authors.affiliation: Department of Botany, University of Wisconsin, Madison, 430 Lincoln Dr., Madison, WI, 53706, USA.
authors.forename: Alison Dawn
authors.initials: AD
authors.lastname: Scott
authors.affiliation: Department of Botany, University of Wisconsin, Madison, 430 Lincoln Dr., Madison, WI, 53706, USA.
authors.forename: Noah W M
authors.initials: NW
authors.lastname: Stenz
authors.affiliation: Department of Ecology and Environmental Science, Umeå Plant Science Centre, Umeå University, SE-901 87, Umeå, Sweden.
authors.forename: Pär K
authors.identifier: 0000-0001-9225-7521
authors.initials: PK
authors.lastname: Ingvarsson
authors.affiliation: Department of Botany, University of Wisconsin, Madison, 430 Lincoln Dr., Madison, WI, 53706, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Baum
mesh_terms: D005075:Biological Evolution; D018745:Genome, Plant; D010802:Phylogeny; D011123:Polyploidy; D032487:Sequoia / Q000235:genetics*; D064028:Tracheophyta / Q000235:genetics
keywords: Sequoia sempervirens; conifer; gymnosperm; hexaploid; multisomic inheritance; polyploidy; whole genome duplication (WGD)