Russian dandelion [Taraxacum kok-saghyz (TKS)] is an herbaceous perennial that can also be grown as an annual. Latex can be found in the root, in specialized cells called laticifers (Whaley and Bowen, 1947) and this species could be a source of natural rubber, essential for the fabrication of over 40,000 products vital to industries including transportation, health care, and construction (Mooibroek and Cornish, 2000). TKS grows well in southern Ontario and the northern United States, and it is currently under development as a new crop to introduce natural rubber production to these regions (van Beilen and Poirier, 2007).
The transition from vegetative to reproductive development in plants is cued by endogenous, as well as environmental signals, such as photoperiod and temperature (Thomas et al., 2006). TKS can require a period of cool temperatures, known as vernalization, to induce flowering (Borthwick et al., 1943). This is common in temperate perennials because it encourages flowering after winter, during the favorable conditions of spring (Andres and Coupland, 2012). Although the natural distribution of TKS is restricted to a relatively small area along the Alatau mountain range in Kazakhstan, the species can grow in a number of regions with favorable climates (Whaley and Bowen, 1947).
Variation for flowering habit is observed in natural populations. Early flowering, spring-type, plants do not require vernalization and flower ≈50 d after planting in a greenhouse with a 16-h photoperiod (K.J.M. Hodgson-Kratky and D.J. Wolyn, unpublished data). Winter-type plants, in contrast, grow vegetatively and generally will not flower without a cold period (Hodgson-Kratky et al., 2015).
The floral induction pathway has been studied extensively in the model plant, Arabidopsis thaliana. In this species, two major loci determine flowering habit: flowering locus C (FLC) and frigida (FRI) (Koornneef et al., 1994). Winter-type plants carry dominant functional alleles at each of these two loci, and homozygous recessive genotypes with inactive fri and/or flc alleles result in early flowering (Gendall and Simpson, 2006; Johanson et al., 2000). Control of flowering through FLC/FRI is conserved in many plant species (Irwin et al., 2012; Kuittinen et al., 2008; Reeves et al., 2007; Risk et al., 2010; Schranz et al., 2002; Zhang et al., 2009).
The genetic pathway controlling the vernalization requirement for flowering in temperate cereals, such as wheat (Triticum aestivum), barley (Hordeum vulgare), and rye (Secale cereale), evolved independently of that in A. thaliana, and is regulated primarily by three genes: Vernalization 1 (VRN1) (Yan et al., 2003), VRN2 (Yan et al., 2004), and VRN3 (Yan et al., 2006). Spring-type plants possess recessive null mutations at the VRN2 locus (Dubcovsky et al., 2005; Yan et al., 2004) or dominant mutations in the promoter region of VRN1 (Dubcovsky et al., 2005; Fu et al., 2005; Tranquilli and Dubcovsky, 2000; Yan et al., 2004) or VRN3, which cause high expression in these two genes regardless of environmental conditions (Yan et al., 2006).
Flowering habit is an important trait in TKS breeding because winter-type plants have higher rubber yields than spring-type plants (Whaley and Bowen, 1947). Therefore, populations under development for high rubber are also selected for vernalization requirement and thus it would be useful to understand the inheritance of flowering habit. Based on the genetic pathways identified in A. thaliana and cereals, multiple interacting loci influencing the trait are predicted in TKS. The objectives of this research were to determine the number of major genes controlling the vernalization requirement in TKS and interlocus interactions.
BowleyS.2008A hitchhiker’s guide to statistics in biology. 2nd ed. Any Old Subject Books Guelph ON Canada
DubcovskyJ.ChenC.YanL.2005Molecular characterization of the allelic variation at the VRN-H2 vernalization locus in barleyMol. Breed.15395407
FuD.SzűcsP.YanL.HelgueraM.SkinnerJ.S.von ZitzewitzJ.HayesP.M.DubcovskyJ.2005Large deletions within the first intron in VRN-1 are associated with spring growth habit in barley and wheatMol. Genet. Genomics2735465
GendallA.R.SimpsonG.G.2006Vernalization p. 26–49. In: B.R. Jordan (ed.). The molecular biology and biotechnology of flowering. CABI Intl. Wallingford UK
Hodgson-KratkyK.J.M.DemersM.N.K.StoffynO.M.WolynD.2015Harvest date, post-harvest vernalization and regrowth temperature affect flower bud induction in russian dandelion (Taraxacum kok-saghyz)Can. J. Plant Sci.9512211228
IrwinJ.A.ListerC.SoumpourouE.ZhangY.HowellE.C.TeakleG.DeanC.2012Functional alleles of the flowering time regulator FRIGIDA in the Brassica oleracea genomeBMC Plant Biol.1221
JohansonU.WestJ.ListerC.MichaelsS.AmasinoR.DeanC.2000Molecular analysis of FRIGIDA, a major determinant of natural variation in Arabidopsis flowering timeScience290344347
KoornneefM.Blankestijn-de VriesH.HanhartC.SoppeW.PeetersT.1994The phenotype of some late flowering mutants is enhanced by a locus on chromosome 5 that is not effective in the Landsberg erecta wild-typePlant J.6911919
KuittinenH.NiittyvuopioA.RinneP.SavolainenO.2008Natural variation in Arabidopsis lyrata vernalization requirement conferred by a FRIGIDA indel polymorphismMol. Biol. Evol.25319329
ReevesP.A.HeY.SchmitzR.J.AmasinoR.M.PanellaL.W.RichardsC.M.2007Evolutionary conservation of the FLOWERING LOCUS-mediated vernalization response: Evidence from the sugar beet (Beta vulgaris)Genetics176295307
RiskJ.M.LaurieR.E.MacknightR.C.DayC.L.2010FRIGIDA and related proteins have a conserved central domain and family specific N- and C- terminal regions that are functionally importantPlant Mol. Biol.73493505
SchranzM.E.QuijadaP.SungS.B.LukensL.AmasinoR.OsbornT.C.2002Characterization and effects of the replicated flowering time gene FLC in Brassica rapaGenetics16214571468
ThomasB.CarreI.JacksonS.2006Photoperiodism and flowering p. 3–25. In: B.R. Jordan (ed.). The molecular biology and biotechnology of flowering. CAB Intl. Wallingford UK
WhaleyW.G.BowenJ.S.1947Russian dandelion (kok-saghyz) an emergency source of natural rubber. U.S. Govt. Printing Office Misc. Publ. No. 618
YanL.FuD.LiC.BlechlA.TranquilliG.BonafedeM.SanchezA.ValarikM.YasudaS.DubcovskyJ.2006The wheat and barley vernalization gene VRN3 is an orthologue of FTProc. Natl. Acad. Sci. USA1031958119586
YanL.LoukoianovA.BlechlA.TranquilliG.RamakrishnaW.SanMiguelP.BennetzenJ.L.EcheniqueV.DubcovskyJ.2004The wheat VRN2 gene is a flowering repressor down-regulated by vernalizationScience30316401644
YanL.LoukoianovA.TranquilliG.HelgueraM.FahimaT.DubcovskyJ.2003Positional cloning of the wheat vernalization gene VRN1Proc. Natl. Acad. Sci. USA10062636268
ZhangJ.LiZ.YaoJ.HuC.2009Identification of flowering-related genes between early flowering orange mutant and wild-type trifoliate orange [Poncirus trifoliate (L.) Raf.] by suppression subtraction hybridization (SSH) and microarrayGene43095104