Karyotypes, heterochromatin, and physical mapping of 18S-26S rDNA in Cactaceae

Abstract

Karyotype analyses in members of the four Cactaceae subfamilies were performed. Numbers and karyotype formula obtained were: Pereskioideae = Pereskiaaculeata(2n = 22; 10 m + 1 sm), Maihuenioideae = Maihuenia patagonica (2n = 22, 9 m + 2 sm; 2n = 44, 18 m + 4 sm), Opuntioideae = Cumulopuntia recurvata(2n = 44; 20 m + 2 sm), Cactoideae = Acanthocalycium spiniflorum (2n = 22; 10 m + 1 sm),Echinopsis tubiflora (2n = 22; 10 m + 1 sm), Trichocereus candicans (2n = 22, 22 m). Chromosomes were small, the average chromosome length was 2.3 μm. Diploid species and the tetraploid C. recurvata had one terminal satellite, whereas the remaining tetraploid species showed four satellited chromosomes. Karyotypes were symmetrical. No CMA^–/DAPI⁺ bands were detected, but CMA⁺/DAPI^– bands associated with NOR were always found. Pericentromeric heterochromatin was found in C. recurvata, A. spiniflorum, and the tetraploid cytotype of M. patagonica. The locations of the 18S-26S rDNA sites in all species coincided with CMA⁺/DAPI^– bands; the same occurred with the sizes and numbers of signals for each species. This technique was applied for the first time in metaphase chromosomes in cacti. NOR-bearing pair no.1 may be homeologous in all species examined. In Cactaceae, the 18S-26S loci seem to be highly conserved.

Molecular cytogenetic insights into the evolution of the epiphytic genusLepismium(Cactaceae) and related genera

“…The meagre data available on heterochromatin in cacti (Las Peñas et al ., , , , ; our data) show that CMA + /DAPI – blocks are always present at a terminal position associated with the chromosome pair with secondary constrictions. Thus, this character may be conserved in Cactaceae, although more data are needed.…”

“…All species of Lepismium , Rhipsalis and Pfeiffera studied had small chromosomes and symmetrical karyotypes, as is typical in Cactaceae (e.g. Ross, ; Pankin, ; Das & Mohanty, ; Las Peñas et al ., , , ). Among these genera, variation in karyotype composition was rare with respect to chromosome size and morphology.…”

Next generation sequencing analysis reveals a relationship between rDNA unit diversity and locus number in Nicotiana diploids

“…However, unlike the pattern we report here, intragenomic homogeneity is similar in coding and non-coding regions of each species, although slightly higher variation was observed in Drosophila, where rDNA sequences are located at several chromosomal loci. In explaining the level of variation, it is suggestive that the Rosaceae [60,61] and Cactaceae [9], in which large numbers of ITS variants were observed, also have a high (>5) number of rDNA loci [62,63]. A comparable pattern is reported within the grasshopper species Podisma pedestris , in which some populations have a larger number of rDNA loci and a greater complexity of rDNA units [64].…”

Contenido de ADN y patrón de genes ribosomales en el género monotípico Stetsonia (Cactaceae).

“…Herramientas como el bandeo cromosómico fluorescente e hibridación in situ fluorescente (FISH) permiten identificar homologías cromosómicas inter o intra específicas, y son ampliamente usadas en cariosistemática (Greilhuber, 1984). En poblaciones argentinas se han realizado estudios citogenéticos para algunos géneros de cactus (Das & Mohanty, 2006;Las Peñas et al, 2009 pero de Stetsonia sólo se conoce el número cromosómico (2n= 22; Bauk & Las Peñas, 2012).…”