The genus Cercis L. (Fabaceae: Caesalpinoideae: Cercideae), also known as redbud, is a valuable commodity in the North American landscape industry and can be found growing in temperate environments across the globe. Cercis consists of ≈10 species (Davis et al., 2002; Fritsch et al., 2009), which can be found in North America (C. canadensis L., Cercis occidentalis Torr. ex A. Gray), Asia (C. chinensis Bunge, Cercis chingii Chun, Cercis chuniana P.F. Metcalf, Cercis gigantea W.C. Cheng & Keng f., Cercis glabra Pamp, Cercis racemosa Oliv., and Cercis siliquastrum L.), and the Middle East (Cercis griffithii Boiss.). Redbud is recognized for a variety of interesting morphological characteristics, many of which make them ideal ornamental specimens. Valuable insight into angiosperm evolution can be obtained through genetic surveys of this valuable landscape commodity.
Fabaceae, one of the most successful lineages of flowering plants (Legume Phylogeny Working Group et al., 2013) has long been the subject of genomics and genetic research. In particular, species like Lotus japonicus (Regel) K. Larsen and Medicago truncatula Gaertner have been adopted internationally as genetic models for legume-based research thanks to their model characteristics (Udvardi et al., 2005). Caesalpinoideae, a subfamily in which Cercideae resides, contains much of the evolutionary and genetic diversity found in all of Fabaceae. However, recent studies have focused on cultivated legume crops, all of which have diverged relatively recently (Young et al., 2003). This information covers only a fraction of the great diversity that can be found within Fabaceae (Doyle and Luckow, 2003) and could be further supplemented by studying a basal, non-nitrogen fixing member of Fabaceae such as Cercis.
Cercis, an ancient member of Caesalpinoideae, has fossil records that date back to the Eocene era (Jia and Manchester, 2014), and is therefore a prime candidate for a comprehensive study of genome size as it relates to legume systematics and taxonomy. Most aspects of legume biology, from ploidy number to floral diversity, can be further examined through the evolutionary relationships that exist among leguminous taxa (Young et al., 2003). This information could grant valuable insight into species evolution and provide potential breeding applications (Rounsaville and Ranney, 2010) in future Cercis hybridization projects.
Information derived from a genome survey of Cercis will be useful as it relates to a better understanding of the evolution of genome size and ploidy distribution within the legumes. Three cultivars of Cercis warrant particular interest in regard to ploidy variation. Traveller is a unique cultivar of C. canadensis var. texensis possessing both male and female sterility. The basis of this sterility is unknown, but potentially could be based on triploidy. Triploid plants often have reduced fertility or sterility. Likewise, ‘Don Egolf’ is a female sterile form of C. chinensis and will be investigated to determine if its sterility is due to triploidy. Finally, ‘Tom Thumb’ a diminutive sterile form of C. canadensis with extremely small leaves and flowers will be investigated to determine if its unique characters are potentially due to haploidy. Haploid plants have been shown to exhibit dwarfism in other woody species (Yahata et al., 2005). This survey will also contribute to the knowledge of the taxonomic relationship of Bauhinia to redbud. Cercis has been documented as having seven chromosome pairs with 2n = 2x = 14 (Curtis, 1976; Goldblatt, 1981). Bauhinia is thought to be a tetraploid (2n = 4x = 28) relative of Cercis (Doyle and Luckow, 2003) with 14 chromosome pairs (Turner, 1956). As the closest living relative of redbud (Coskun and Parks, 2009), Bauhinia will serve as an interesting comparison with the relative DNA estimations of Cercis in this study.
Cercis chinensis possesses a relatively small genome size of 350 million bps (Mb) (De Mita et al., 2014), which corresponds with the phylogenetic position of significant antiquity (Zou et al., 2008) that Cercis occupies within Fabaceae. Except for C. chinensis, there are currently no other reports of genome size of Cercis. The objectives of this study were to examine the genome size of a comprehensive collection of species, botanical varieties, and cultivars of Cercis. Additionally, the genome size of ‘Tom Thumb’, demonstrating morphological characters suggesting haploidy, and of ‘Traveller’ and ‘Don Egolf’, sterile cultivars suggesting triploidy, will be examined.
Bennett, M.D. & Leitch, I.J. 2012 Plant DNA C-values database (release 6.0). <http://www.kew.org/cvalues/>.
Coskun, F. & Parks, C.R. 2009 A molecular phylogenetic study of red buds (Cercis L., Fabaceae) based on ITS nrDNA sequences Pak. J. Bot. 41 1577 1586
Davis, C.C., Fritsch, P.W., Li, J. & Donoghue, M.J. 2002 Phylogeny and biogeography of Cercis (Fabaceae): Evidence from nuclear ribosomal ITS and chloroplast ndhF sequence data Syst. Bot. 27 289 302
De Mita, S., Streng, A., Bisseling, T. & Geurts, R. 2014 Evolution of a symbiotic receptor through gene duplications in the legume–rhizobium mutualism New Phytol. 201 961 972
Doyle, J.J. 1998 Phylogenetic perspectives on nodulation: An evolving view of plants and symbiotic bacteria Trends Plant Sci. 3 473 478
Doyle, J.J. & Luckow, M.A. 2003 The rest of the iceberg. Legume diversity and evolution in a phylogenetic context Plant Physiol. 131 900 910
Doyle, J.J., Soltis, P.S. & Soltis, D.E. 2012 Polyploidy and genome evolution. Springer-Verlag, Berlin, Heidelberg, Germany
Fritsch, P.W., Larson, K.W. & Schiller, A.M. 2009 Taxonomic implications of morphological variation in Cercis canadensis (Fabaceae) from Mexico and adjacent parts of Texas Syst. Bot. 34 510 520
Goldblatt, P. 1981 Cytology and the phylogeny of leguminosae, p. 427–464. Advances in legume systematics, part 2. Royal Botanic Gardens, Kew, UK
Huang, H., Tong, Y., Zhang, Q. & Gao, L. 2013 Genome size variation among and within Camellia species by using flow cytometric analysis PLoS One 8 e64981
Jia, H. & Manchester, S.R. 2014 Fossil leaves and fruits of Cercis L. (Leguminosae) from the Eocene of Western North America Intl. J. Plant Sci. 175 601 612
Legume Phylogeny Working Group, A. Bruneau, J.J. Doyle, P. Herendeen, C. Hughes, G. Kenicer, G. Lewis, B. Mackinder, R.T. Pennington, M.J. Sanderson, and M.F. Wojciechowski. 2013. Legume phylogeny and classification in the 21st century: Progress, prospects and lessons for other species-rich clades. Taxon 62:217–248
Leitch, I.J., Chase, M.W. & Bennett, M.D. 1998 Phylogenetic analysis of DNA C-values provides evidence for a small ancestral genome size in flowering plants Ann. Bot. 82 85 94
Rounsaville, T.J. & Ranney, T.G. 2010 Ploidy levels and genome sizes of Berberis L. and Mahonia Nutt. species, hybrids, and cultivars HortScience 45 1029 1033
Schranz, E., Edger, P.P. & Mohammadin, S. 2012 Ancient whole genome duplications novelty and diversification: The WGD radiation lag-time model Curr. Opin. Plant Biol. 15 147 153
Soltis, D.E. & Burleigh, J.G. 2009 Surviving the K-T mass extinction: New perspectives of polyploidization in angiosperms Proc. Natl. Acad. Sci. U.S.A. 106 5455 5456
Udvardi, M.K., Tabata, S., Parniske, M. & Stougard, J. 2005 Lotus japonicus: Legume research in the fast lane Trends Plant Sci. 10 222 228
Yahata, M., Harusaki, S., Komatsu, H., Takami, K., Kunitake, H., Yabuya, T., Yamashita, K. & Toolapong, P. 2005 Morphological characterization and molecular verification of a fertile haploid pummelo (Citrus grandis Osbeck) J. Amer. Soc. Hort. Sci. 130 34 40
Zou, P., Liao, J. & Zhang, D. 2008 Leaf epidermal micromorphology of Cercis (Fabaceae: Caesalpinioideae) Bot. J. Linn. Soc. 158 539 547