Unraveling the karyotype structure of the spurges Euphorbia hirta Linnaeus, 1753 and E. hyssopifolia Linnaeus, 1753 (Euphorbiaceae) using genome size estimation and heterochromatin differentiation

Abstract

Euphorbia Linnaeus, 1753 (Euphorbiaceae) is one of the most diverse and complex genera among the angiosperms, showing a huge diversity in morphologic traits and ecologic patterns. In order to improve the knowledge of the karyotype organization of Euphorbia hirta (2n = 18) and Euphorbia hyssopifolia (2n = 12), cytogenetic studies were performed by means of conventional staining with Giemsa, genome size estimations with flow cytometry, heterochromatin differentiation with chromomycin A3 (CMA) and 4’,6-diamidino-2-phenylindole (DAPI) and Giemsa C-banding, fluorescent in situ hybridization (FISH) with 45S and 5S rDNA probes, and impregnation with silver nitrate (AgNO3). Our results revealed small metacentric chromosomes, CMA+/DAPI0 heterochromatin in the pericentromeric regions of all chromosomes and CMA+/DAPI− in the distal part of chromosome arms carriers of nucleolar organizing regions (NORs). The DNA content measurements revealed small genomes for both species: Euphorbia hirta with 2C = 0.77 pg and Euphorbia hyssopifolia with 2C = 1.41 pg. After FISH procedures, Euphorbia hirta, and Euphorbia hyssopifolia presented three and four pairs of terminal 45S rDNA sites, respectively, colocalizing with CMA+ heterochromatic blocks, besides only one interstitial pair of 5S rDNA signals. Additionally, the maximum number of active NORs agreed with the total number of observed 45S rDNA sites. This work represents the first analysis using FISH in the subfamily Euphorbioideae, revealing a significant number of chromosomal markers, which may be very helpful to understand evolutionary patterns among Euphorbia species.

Karyotype and genome size comparative analyses among six species of the oilseed-bearing genus Jatropha (Euphorbiaceae)

“…The pericentromeric heterochromatin in J. curcas is at least partially related to gypsy -type retrotransposons ( Alipour et al , 2014 ), while terminal heterochromatic dots are related to copia -type retrotransposons ( Alipour et al , 2013 ). These patterns of heterochromatin rich karyotypes have also been described for other Euphorbiaceae species, such as castor ( Ricinus communis L.), Euphorbia characias L., E. hirta L., E. hyssopifolia L., Manihot dichotoma Ule and M. esculenta Crantz ( Carvalho and Guerra, 2002 ; D’Emerico et al , 2003 ; Vasconcelos et al , 2010 ; Santana et al , 2016 ).…”

“…Both the number and the distribution patterns of 5S and 45S rDNA sites seem to be quite conserved in Jatropha , although the superposition of 5S and 45S rDNA sites and the presence of 5S rDNA in more than one chromosome pair in J. mollissima are reported for the first time in a species of Euphorbiaceae (see, for instance, Carvalho and Guerra, 2002 ; Vasconcelos et al , 2010 ; Santana et al , 2016 ). Furthermore, the presence of both 5S and 45S rDNA sites in the same chromosome arm is not common in the family, and it has been observed only in E. hyssopifolia so far ( Santana et al. , 2016 ).…”

Karyotype report for eight <i>Euphorbia</i> taxa cultivated in Turkey

“…One of the most diverse and complicated angiosperm genera Euphorbia displays a wide range of physical characteristics, ecological patterns, and karyotypic features (Santana et al 2016). In systematic studies, the chromosomal organization from karyological examina-tions can be particularly instructive (Tian et al 2018).…”