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. 2014 Jul;197(3):969-79.
doi: 10.1534/genetics.114.165548. Epub 2014 Apr 26.

Chromosomal evolution and patterns of introgression in helianthus

Jessica G Barb  1 , John E Bowers  1 , Sebastien Renaut  2 , Juan I Rey  3 , Steven J Knapp  3 , Loren H Rieseberg  2 , John M Burke  4
Affiliations

Chromosomal evolution and patterns of introgression in helianthus

Jessica G Barb et al. Genetics. 2014 Jul.

Abstract

Knowledge of the nature and extent of karyotypic differences between species provides insight into the evolutionary history of the genomes in question and, in the case of closely related species, the potential for genetic exchange between taxa. We constructed high-density genetic maps of the silverleaf sunflower (Helianthus argophyllus) and Algodones Dune sunflower (H. niveus ssp. tephrodes) genomes and compared them to a consensus map of cultivated sunflower (H. annuus) to identify chromosomal rearrangements between species. The genetic maps of H. argophyllus and H. niveus ssp. tephrodes included 17 linkage groups each and spanned 1337 and 1478 cM, respectively. Comparative analyses revealed greater divergence between H. annuus and H. niveus ssp. tephrodes (13 inverted segments, 18 translocated segments) than between H. annuus and H. argophyllus (10 inverted segments, 8 translocated segments), consistent with their known phylogenetic relationships. Marker order was conserved across much of the genome, with 83 and 64% of the H. argophyllus and H. niveus ssp. tephrodes genomes, respectively, being syntenic with H. annuus. Population genomic analyses between H. annuus and H. argophyllus, which are sympatric across a portion of the natural range of H. annuus, revealed significantly elevated genetic structure in rearranged portions of the genome, indicating that such rearrangements are associated with restricted gene flow between these two species.

Keywords: comparative mapping; gene flow; genome rearrangement; karyotypic evolution; reproductive isolation.

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Figures

Figure 1
Figure 1
Genetic linkage maps of Helianthus argophyllus (ARG) and H. niveus ssp. tephrodes (NIV). ARG and NIV linkage groups (LGs) are labeled and color coded based on macrosynteny with H. annuus (ANN) chromosomes ANN1–17 (Bowers et al. 2012). Gray segments contain markers that are mapped to multiple ANN LGs not including that particular ARG or NIV LG; cross-hatching indicates a region that is inverted relative to ANN; black arrows indicate translocated segments that are also inverted relative to ANN. The scale on the left is in centimorgans (cM). See Figure S2 for more detail.
Figure 2
Figure 2
Genetic maps of Helianthus argophyllus (ARG) and H. niveus ssp. tephrodes (NIV) compared to a consensus map of H. annuus (ANN) from Bowers et al. 2012. Color coding and chromosome nomenclature follow Figure 1. Homologous markers are connected by lines. Only ANN markers mapped in ARG or NIV are included. See Figure S3 and Figure S4 for more detail.
Figure 2
Figure 2
Genetic maps of Helianthus argophyllus (ARG) and H. niveus ssp. tephrodes (NIV) compared to a consensus map of H. annuus (ANN) from Bowers et al. 2012. Color coding and chromosome nomenclature follow Figure 1. Homologous markers are connected by lines. Only ANN markers mapped in ARG or NIV are included. See Figure S3 and Figure S4 for more detail.
Figure 2
Figure 2
Genetic maps of Helianthus argophyllus (ARG) and H. niveus ssp. tephrodes (NIV) compared to a consensus map of H. annuus (ANN) from Bowers et al. 2012. Color coding and chromosome nomenclature follow Figure 1. Homologous markers are connected by lines. Only ANN markers mapped in ARG or NIV are included. See Figure S3 and Figure S4 for more detail.
Figure 3
Figure 3
Genome-wide divergence (FST) between Helianthus annuus (ANN) and H. argophyllus (ARG) in syntenic and rearranged regions of the genome. Syntenic portions of the genome are colored in gray, rearranged portions are in red, and the 5-cM regions neighboring the rearrangements are in yellow. The horizontal dashed line represents mean genome-wide FST. Linkage groups in ANN and their corresponding location in ARG are pictured below the x-axis. Inverted chromosomal segments are pictured in green, while translocated segments in ARG are in blue, orange, light purple, or dark purple.
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