Karyotype differentiation of four Cestrum species (Solanaceae) based on the physical mapping of repetitive DNA

Abstract

We studied the karyotypes of four Brazilian Cestrum species (C. amictum, C. intermedium, C. sendtnerianum and C. strigilatum) using conventional Feulgen staining, C-Giemsa and C-CMA 3 /DAPI banding, induction of cold-sensitive regions (CSRs) and fluorescent in situ hybridization (FISH) with rDNA probes. We found that the karyotypes of all four species was 2n = 2x = 16, with, except for the eighth acrocentric pair, a predominance of meta-and submetacentric chromosomes and various heterochromatin classes. Heterochromatic types previously unreported in Cestrum as neutral C-CMA 3 0 /DAPI 0 bands, CMA 3 + bands not associated with NORs, and C-Giemsa/CSR/DAPI -bands were found. The heterochromatic blocks varied in size, number, position and composition. The 45S rDNA probe preferentially located in the terminal and subterminal regions of some chromosomes, while 5S rDNA appeared close to the centromere of the long arm of pair 8. These results suggest that karyotype differentiation can occur mainly due to changes in repetitive DNA, with little modification in the general composition of the conventionally stained karyotype.

Chromosomal differentiation of Tribe Cestreae (Solanaceae) by analyses of 18-5.8-26S and 5S rDNA distribution

“…Our results confirm previous works on Cestrum strigilatum and Sessea regnellii (Fregonezi et al 2006;Fernandes et al 2009) and report new data about distribution of 18-5.8-26S and 5S rDNA sites in C. elegans, C. euanthes, C. fasciculatum, C. kunthii, C. lorentzianum, C. nocturnum, C. parqui, C. tomentosum, and Vestia foetida. All species studied of Cestreae have conserved the terminal and pericentromeric positions for 18-5.8-26S and 5S rDNA, respectively.…”

“…The basic number x = 8 is conserved in Cestreae and differentiates it from other Solanaceae. Our results confirm previous numbers of several species from other localities (Tschischow 1956;Sharma and Sharma 1957;Bolkhovskikh et al 1969;Moscone 1992;Las Peñas et al 2006;Fregonezi et al 2006;Fernandes et al 2009), being the first chromosome number report for Cestrum euanthes, C. kunthii, C. lorentzianum, and C. tomentosum.…”

“…Tribe Cestreae is additionally characterized by large chromosomes and symmetrical karyotypes (Fregonezi et al 2006;Las Peñas et al 2006;Fernandes et al 2009). Karyotypes of the studied species are relatively symmetrical, have similar chromosome sizes, and are composed exclusively of m chromosomes (Vestia foetida) or with one sm pair (the remaining species).…”

“…a Cestrum nocturnum, b C. parqui, c C. euanthes. Bar = 1 lm species of Cestrum studied to date (Fregonezi et al 2006;Fernandes et al 2009;this work). On the contrary, the 18-5.8-26S rDNA distribution allows to define two groups in Cestrum: one characterized by the synteny of the rDNA in the only sm pair (C. amictum, C. corymbosum, C. elegans, C. fasciculatum, C. intermedium, C. nocturnum, and C. strigilatum), and another one with a 18-5.8-26S rDNA distribution independent of the 5S rDNA loci (C. euanthes, C. kunthii, C. laevigatum, C. lorentzianum, C. megalophylum, C. parqui, C. sendtnerianum, and C. tomentosum).…”

“…Karyotypically, Cestreae is outstanding within Solanaceae because of the following features, which support its monophyly and make it of interest to study karyotype evolution and diversity of distribution of repetitive DNA sequences: (1) basic number x = 8 (Tschischow 1956;Bolkhovskikh et al 1969;Goldblatt 1984;Goldblatt andJohnson 1991, 1996;Las Peñas et al 2006); (2) largest chromosome sizes among the family (Fernandes et al 2009;Fregonezi et al 2006;Las Peñas et al 2006); (3) complex patterns of heterochromatin in Cestrum, like the cold-sensitive regions Greilhuber 1992, 1993;Fregonezi et al 2006); (4) occurrence of B-chromosomes in several Cestrum species with particular banding patterns (Fregonezi et al 2004) and distribution of 45S and 5S rDNA (Sykorova et al 2003b;Fernandes et al 2009); and (5) absence of Arabidopsis-type (TTTAGGG)n telomeres, which seem to be replaced by an A/T-rich minisatellite (Sykorova et al 2003a, b).…”