The genetic basis of floral symmetry is a topic of great interest because of its effect on pollinator behavior and, consequently, plant diversification. The Asteraceae, which is the largest family of flowering plants, is an ideal system in which to study this trait, as many species within the family exhibit a compound inflorescence containing both bilaterally symmetric (i.e., zygomorphic) and radially symmetric (i.e., actinomorphic) florets. In sunflower and related species, the inflorescence is composed of a single whorl of ray florets surrounding multiple whorls of disc florets. We show that in double-flowered (dbl) sunflower mutants (in which disc florets develop bilateral symmetry), such as those captured by Vincent van Gogh in his famous nineteenth-century sunflower paintings, an insertion into the promoter region of a CYCLOIDEA (CYC)-like gene (HaCYC2c) that is normally expressed specifically in WT rays is instead expressed throughout the inflorescence, presumably resulting in the observed loss of actinomorphy. This same gene is mutated in two independent tubular-rayed (tub) mutants, though these mutations involve apparently recent transposon insertions, resulting in little or no expression and radialization of the normally zygomorphic ray florets. Interestingly, a phylogenetic analysis of CYC-like genes from across the family suggests that different paralogs of this fascinating gene family have been independently recruited to specify zygomorphy in different species within the Asteraceae.

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.C HROMOSOMAL rearrangements are of considerable interest because they are often associated with barriers to gene flow between related species, either due to their direct effects on the fitness of heterozygotes or through the indirect effects of genic barriers embedded within them (White 1978;Barton and Bengtsson 1986;Rieseberg et al. 1995bRieseberg et al. , 1999Rieseberg 2001;Navarro and Barton 2003;Kirkpatrick and Barton 2006; reviewed in Faria and Navarro 2010;Gimenez et al. 2012). As such, detailed information on karyotypic differences between species provides insight into the nature of reproductive isolation and, more pragmatically, informs attempts to introgress beneficial alleles from wild species into crop gene pools (Chetelat and Meglic 2000;Foulongne et al. 2003;Dirlewanger et al. 2004). An improved understanding of synteny across species can also facilitate the identification and localization of functionally important genes in a taxon of interest through the extrapolation of gene order from model species (e.g., Choi et al. 2004;Dilbirligi et al. 2006).The genus Helianthus, which is composed of 49 species native to the Americas (Timme et al. 2007) and includes cultivated sunflower (Helianthus annuus L.; 2n = 2x = 34; hereafter referred to as ANN), has emerged as a model for genetic studies of adaptation, hybridization, and speciation (Rieseberg et al. 1995a,b;Lai et al. 2005;Reagon and Snow 2006;Massinga et al. 2009;Gutierrez et al. 2010;Vekemans 2010;Roumet et al. 2013). Insight into the nature and extent of reproductive barriers within Helianthus will ...

The perennial grass triploid Miscanthus 9 giganteus is a promising renewable bioenergy feedstock in the United States and Europe. Originating from eastern Asia, this species is a sterile hybrid cross between M. sinensis and M. sacchariflorus. While research has begun to examine the impacts of M. sinensis and triploid M. 9 giganteus on the landscape, M. sacchariflorus has been largely overlooked in the peer-reviewed literature. This review article discusses the origin, uses, distribution, and invasive potential of M. sacchariflorus. M. sacchariflorus is capable of producing high yields (10.7 t DM ha À1 yr À1 ), generally does not reproduce by seed, and can be challenging to establish due to poor cold tolerance, likely due to the limited germplasm used in evaluations. However, M. sacchariflorus has abundant and aggressively spreading rhizomes, which underscores its invasive risk. In the United States, it is listed as escaped from cultivation in at least eight states, primarily in the Midwest, although it is likely that not all populations have been reported. As such, it is essential to generate a comprehensive dataset of all known M. sacchariflorus populations and monitor any continued spread of this species.

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Stokes aster [Stokesia laevis (J. Hill) Greene] is a herbaceous perennial endemic to the coastal plains of the southeastern United States. Anthocyanin and copigment aglycones from flowers were characterized using high-performance liquid chromatography. Blue, lavender, violet, and albescent flowers each contained the anthocyanidin petunidin, although albescent flowers contained a substantially smaller amount. Pale pink flowers were found to contain only cyanidin. Anthocyanins and carotenoids were not present in pale yellow flowers of this species. All flowers contained the flavone luteolin. Genetic analysis of F1, F2, and BC1 populations suggested that flower color in stokes aster is controlled by at least three loci. F2 populations of blue × albescent and blue × pale yellow flowering plants segregated in a 3:1 ratio of blue to albescent or pale yellow flowered progeny, indicating that albescent and pale yellow flower colors were recessive and each controlled by a single locus with two alleles. BC1 populations supported these results. We propose the symbols A and Y: AA and YY plants synthesize a normal amount of anthocyanins, aa plants synthesize a reduced amount of anthocyanins, and yy plants do not synthesize anthocyanins. When the two mutant phenotypes (i.e., albescent [aa] and pale yellow [yy]) were crossed, the F1s were blue, and the F2 segregated in a 9 blue:3 albescent:4 yellow ratio, indicating that the recessive locus (y), when homozygous, was epistatic to other loci involved in anthocyanin production (e.g., A), and that the genotypes of the parents used in these crosses were aaYY (albescent) and AAyy (pale yellow). F1, F2, and BC1 populations of blue (petunidin) × pale pink (cyanidin) flowering plants revealed that cyanidin production was recessive and controlled by a single locus, P, with two alleles, whereby PP plants synthesize petunidin and pp plants synthesize cyanidin. It was difficult to distinguish albescent- and pale pink-flowered progeny in segregating generations, therefore three genetic models were proposed and tested to determine the genotype(s) (i.e., AApp, Aapp, or aapp) of the pale pink-flowered plants. Based on these analyses, we propose a theoretical biochemical pathway for flavonoid biosynthesis in stokes aster.

Stokesia laevis (J. Hill) Greene is a herbaceous perennial native to the southeastern United States. Most cultivars of Stokesia are diploid (2n = 2x = 14) except for ‘Omega Skyrocket’, a tetraploid (2n = 4x = 28) form selected from a natural population. A comparative study of the karyotypes and meiotic behavior of diploid cultivars, seed-derived accessions of ‘Omega Skyrocket’, synthetically derived autotetraploids, and triploid progeny from these taxa strongly suggest that ‘Omega Skyrocket’ is an autotetraploid form of Stokesia. Total karyotype length, 161 μm and 293 μm, and average chromosome length, 11.5 μm and 10.5 μm, of the diploid cultivars and tetraploid accessions of ‘Omega Skyrocket’, respectively, were determined. The karyotype of the diploid cultivars consisted of eight metacentric (m) and six submetacentric (sm) chromosomes with average arm ratio values ranging from 1.12 to 2.06. The karyotype of ‘Omega Skyrocket’ consisted of 23 m chromosomes and 5 sm chromosomes with average arm ratio values ranging from 1.22 to 2.02. Meiotic pairing in the diploids was normal. No meiotic irregularities such as laggards or bridges were observed and disjunction was balanced (7:7). Accessions of ‘Omega Skyrocket’ demonstrated a high frequency (60%) of quadrivalent formation; however, later stages of meiosis were regular with balanced disjunction (14:14) occurring in 95% of the cells. Meiotic configurations in synthetically derived autotetraploids and triploid hybrids from crosses of diploid cultivars × ‘Omega Skyrocket’ consisted of univalents, bivalents, trivalents, quadrivalents, and pentavalents. Abnormalities, including laggards, unequal and/or premature disjunction, chromosome bridges, and chromosome stickiness were observed. Average nuclear 2C DNA content was 20.3 pg for the diploid cultivars and 39.9 pg for the newly synthesized autotetraploids. Average nuclear 2C DNA content for ‘Omega Skyrocket’ was 37.3 pg, which was 8.2% less than twice the average 2C DNA content of the diploid accessions and 6.4% less than the newly synthesized autotetraploids, suggesting that genomic downsizing in ‘Omega Skyrocket’ has occurred. Similarity of the karyotypes of the diploids and ‘Omega Skyrocket’ and the slight reduction in nuclear DNA content suggest that ‘Omega Skyrocket’ has diverged little from its original diploid progenitor.