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Article|05 Jan 2022|OPEN
Chloroplast phylogenomics in Camelina (Brassicaceae) reveals multiple origins of polyploid species and the maternal lineage of C. sativa
Jordan R. Brock1 , , Terezie Mandáková2 , Michael McKain3 , Martin A. Lysak2 and Kenneth M. Olsen,1 ,
1Department of Biology, Washington University in St. Louis, St. Louis, Missouri, 63130 USA
2CEITEC – Central European Institute of Technology, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic
3Department of Biological Sciences, The University of Alabama, 411 Mary Harmon Bryant Hall, Tuscaloosa, Alabama, 35487 USA
*Corresponding author. E-mail: brock@wustl.edu,kolsen@wustl.edu

Horticulture Research 9,
Article number: uhab050 (2022)
doi: https://doi.org/10.1093/hr/uhab050
Views: 21

Received: 09 Jun 2021
Revised: 09 Aug 2021
Accepted: 25 Aug 2021
Published online: 05 Jan 2022

Abstract

The genus Camelina (Brassicaceae) comprises 7–8 diploid, tetraploid, and hexaploid species. Of particular agricultural interest is the biofuel crop, C. sativa (gold-of-pleasure or false flax), an allohexaploid domesticated from the widespread weed, C. microcarpa. Recent cytogenetics and genomics work has uncovered the identity of the parental diploid species involved in ancient polyploidization events in Camelina. However, little is known about the maternal subgenome ancestry of contemporary polyploid species. To determine the diploid maternal contributors of polyploid Camelina lineages, we sequenced and assembled 84 Camelina chloroplast genomes for phylogenetic analysis. Divergence time estimation was used to infer the timing of polyploidization events. Chromosome counts were also determined for 82 individuals to assess ploidy and cytotypic variation. Chloroplast genomes showed minimal divergence across the genus, with no observed gene-loss or structural variation. Phylogenetic analyses revealed C. hispida as a maternal diploid parent to the allotetraploid Camelina rumelica, and C. neglecta as the closest extant diploid contributor to the allohexaploids C. microcarpa and C. sativa. The tetraploid C. rumelica appears to have evolved through multiple independent hybridization events. Divergence times for polyploid lineages closely related to C. sativa were all inferred to be very recent, at only ~65 thousand years ago. Chromosome counts confirm that there are two distinct cytotypes within C. microcarpa (2n = 38 and 2n = 40). Based on these findings and other recent research, we propose a model of Camelina subgenome relationships representing our current understanding of the hybridization and polyploidization history of this recently-diverged genus.