CMA band variability and physical mapping of 5S and 45S rDNA sites in Brazilian Cactaceae: Pereskioideae and Opuntioideae

Abstract

Representatives of the Cactaceae subfamilies Pereskioideae and Opuntioideae from northeastern Brazil were studied using banding with the fluorochromes, CMA3 and DAPI, as well as with fluorescent in situ hybridization using 45S and 5S rDNA probes to identify the distributions of their heterochromatin and rDNA sites. Pereskia aculeata, P. bahiensis, P. grandifolia (Pereskioideae), Brasilopuntia brasiliensis, Tacinga funalis, and T. palmadora showed 2n = 22, while Opuntia dillenii showed 2n = 44, and O. ficus-indica 2n = 88. The karyotypes of all of the species were symmetric, with average chromosome lengths varying from 1.94 lm in O. dillenii to 3.17 lm in P. aculeata. One pair of terminal CMA? bands corresponding to NORs occurred in all of the diploid cytotypes (except O. ficus-indica, which has two pairs of terminal CMA? bands) as well as in O. dillenii (tetraploid). CMA? bands were also observed in the interstitial region of the long arm of a chromosome pair in B. brasiliensis, while a number of variable proximal bands were observed on three chromosome pairs in O. dillenii and on most of the chromosomes of O. ficus-indica. The 45S rDNA sites corresponded to the terminal CMA? bands, while the 5S rDNA sites were located in the interstitial regions of the long arms of the chromosome pairs of P. aculeata, P. bahiensis, P. grandifolia, and B. brasiliensis. Our data, and earlier publications, suggest that the subfamily Opuntioideae can be characterized as having proximal/interstitial CMA? heterochromatin in at least one chromosome pair (except in Tacinga). The absence of proximal heterochromatic bands, however, appears to be a synapomorphy of the basal lineages of Cactaceae (subfamily Pereskioideae ? Maihuenioideae), suggesting that karyotypes with heterochromatin restricted to the terminal region of a chromosome pair (45S rDNA) represent a plesiomorphic character of the family.

Karyotype characterization and evolution of chromosome number in Cactaceae with special emphasis on subfamily Cactoideae

“…Fluorescent in situ hybridization provides additional chromosome markers for these analyses. The the physical mapping of 45S rDNA exhibited a conserved pattern, with the number of sites strictly correlated with species ploidy: two sites in the diploid species, four sites in the tetraploid species (Peñas et al 2009;Moreno et al 2015;Castro et al 2016; result presented here). All 45S rDNA sites were terminally localized and co-localized with CMA + bands, in agreement with the most common situation observed in plants (Lima- de-Faria 1980;Roa & Guerra 2012).…”

“…The presence of both terminal and proximal CG-rich fluorescent bands detected here seems to be a common characteristic among Cactoideae species (Peñas et al 2008;Moreno et al 2015). Pereskia did not have proximal CMA + bands (Peñas et al 2014;Castro et al 2016), suggesting that the amplification of CG-rich heterochromatin occurred in the common ancestor of Opuntioideae and Cactoideae.…”

“…Pyrrhocactus species, e.g., could be characterized by its variation in pericentromeric CMA + bands (Peñas et al 2008). The genera Opuntia and Brasiliopuntia also exhibit pericentromeric CMA + bands, whereas the related genus Tacinga is characterized by the absence of such pericentromeric CMA + bands (Castro et al 2016). Duplicated 5S rDNA sites are characteristic of most Lepismium clades, but this is absent in the more derived clades (Moreno et al 2015).…”

Heterochromatin and numeric chromosome evolution in Bignoniaceae, with emphasis on the Neotropical clade Tabebuia alliance

“…The pattern of two CMA + telomeric bands (chromosome type A) seen in most species of the Tabebuia alliance is very common among Angiosperms, and usually corresponds to a nucleolar organizer region (Guerra, 2000;Roa and Guerra, 2012). Telomeric CMA bands are most likely related to rDNA sites as seen in most plant species (Barros e Silva et al, 2010;Castro et al, 2016;Marinho et al, 2018). Differences among species could be related tochromosome rearrangements and the amplification and reduction of rDNA sites caused by satellites or transposable sequences (Mehrotra and Goyal, 2014;Evtushenko et al, 2016;Saze, 2018).…”

“…In genera such as Lycium L. (Stiefkens et al, 2010), Pereskia Mill. (Castro et al, 2016), and Ceiba Mill. (Figueredo et al, 2016), however, the heterochromatin pattern appears to be quite conserved and demonstrate only small variability among the different species.…”