Differential Repeat Accumulation in the Bimodal Karyotype of Agave L.

The genus Agave presents a bimodal karyotype with x = 30 (5L, large, +25S, small chromosomes). Bimodality within this genus is generally attributed to allopolyploidy in the ancestral form of Agavoideae. However, alternative mechanisms, such as the preferential accumulation of repetitive elements at the macrochromosomes, could also be important. Aiming to understand the role of repetitive DNA within the bimodal karyotype of Agave, genomic DNA from the commercial hybrid 11648 (2n = 2x = 60, 6.31 Gbp) was sequenced at low coverage, and the repetitive fraction was characterized. In silico analysis showed that ~67.6% of the genome is mainly composed of different LTR retrotransposon lineages and one satellite DNA family (AgSAT171). The satellite DNA localized at the centromeric regions of all chromosomes; however, stronger signals were observed for 20 of the macro- and microchromosomes. All transposable elements showed a dispersed distribution, but not uniform across the length of the chromosomes. Different distribution patterns were observed for different TE lineages, with larger accumulation at the macrochromosomes. The data indicate the differential accumulation of LTR retrotransposon lineages at the macrochromosomes, probably contributing to the bimodality. Nevertheless, the differential accumulation of the satDNA in one group of macro- and microchromosomes possibly reflects the hybrid origin of this Agave accession.

Divide to Conquer: Evolutionary History of Allioideae Tribes (Amaryllidaceae) Is Linked to Distinct Trends of Karyotype Evolution.

Allioideae (e.g., chives, garlics, onions) comprises three mainly temperate tribes: Allieae (800 species from the northern hemisphere), Gilliesieae (80 South American species), and Tulbaghieae (26 Southern African species). We reconstructed the phylogeny of Allioideae (190 species plus 257 species from Agapanthoideae and Amaryllidoideae) based on ITS, matK, ndhF, and rbcL to investigate its historical biogeography and karyotype evolution using newly generated cytomolecular data for Chilean Gilliesieae genera Gethyum, Miersia, Solaria, and Speea. The crown group of Allioideae diversified ∼62 Mya supporting a Gondwanic origin for the subfamily and vicariance as the cause of the intercontinental disjunction of the tribes. Our results support the hypothesis of the Indian tectonic plate carrying Allieae to northern hemisphere ('out-of-India' hypothesis). The colonization of the northern hemisphere (∼30 Mya) is correlated with a higher diversification rate in Allium associated to stable x = 8, increase of polyploidy and the geographic expansion in Europe and North America. Tulbaghieae presented x = 6, but with numerical stability (2n = 12). In contrast, the tribe Gilliesieae (x = 6) varied considerably in genome size (associated with Robertsonian translocations), rDNA sites distribution and chromosome number. Our data indicate that evolutionary history of Allioideae tribes is linked to distinct trends of karyotype evolution.

Comparative cytogenetics of the ACPT clade (Anacampserotaceae, Cactaceae, Portulacaceae, and Talinaceae): a very diverse group of the suborder Cactineae, Caryophyllales.

The clade ACPT (Anacampserotaceae, Cactaceae, Portulacaceae, and Talinaceae) is the most diverse lineage of the subordem Cactineae. The relationships between these families are still uncertain, with different topologies suggested by phylogenetic analyses with several combinations of markers. Different basic numbers (x) have been suggested for each family and for the subord, often in a contestable way. Comparative cytogenetic has helped to understand the evolutionary relationships of phylogenetically poorly resolved groups, as well as their mechanisms of karyotype evolution. The karyotype evolution in representatives of Cactineae was analyzed, focusing on the ACPT clade, through the analysis of chromosome number in a phylogenetic bias. The phylogeny obtained showed a well-resolved topology with support for the monophyly of the five families. Although a chromosomal number is known for less than 30% of the Cactineae species, the analyses revealed a high karyotype variability, from 2n = 8 to 2n = 110. The analysis of character reconstruction of the ancestral haploid numbers (p) suggested p = 12 for Cactineae, with distinct basic numbers for the clade family ACPT: Cactaceae and Montiaceae (p = 11), Talinaceae (p = 12), and Anacampserotaceae and Portulacaceae (p = 9). Talinaceae, Anacampserotaceae, and Cactaceae were stable, while Portulaca and Montiaceae were karyotypically variable. The chromosome evolution of this group was mainly due to events of descending disploidy and poliploidy. Our data confirm that the low phylogenetic resolution among the families of the ACPT clade is due to a divergence of this clade in a short period of time. However, each of these families can be characterized by basic chromosome numbers and unique karyotype evolution events.

Intra- and interspecific chromosome polymorphisms in cultivated Cichorium L. species (Asteraceae).

Endive (Cichorium endivia L.) and chicory (C. intybus L.) both have 2n = 18, but until now, there has been no detailed karyomorphological characterization. The present work evaluated five accessions of each species using FISH with rDNA probes and fluorochrome staining with CMA and DAPI. Both species presented distinct banding patterns after fluorochrome staining: while endive had proximal CMA(++)/DAPI(-) bands in the short arms of pairs 1, 2 and 3, chicory had proximal CMA-positive bands in chromosomes 1 and 3 and interstitial in the short arm of chromosome 8. Among endive accessions, FISH procedures revealed conserved position and number of 5S and 45S rDNA sites (two and three pairs, respectively), associated with the CMA-positive bands. Notwithstanding, polymorphisms were detected within chicory accessions regarding the number and the distribution of rDNA sites in relation to the most frequent karyotype (two pairs with 45S and one with 5S rDNA). The karyological markers developed allowed karyotypic differentiation between both species, uncovering peculiarities in the number and position of rDNA sites, which suggest chromosome rearrangements, such as translocations in chicory cultivars. The interspecific and intraspecific polymorphisms observed emphasize the potential of karyomorphological evaluations, helping our understanding of the relationships and evolution of the group.

Karyotype, C-and fluorescence banding pattern, NOR location and FISH study of five Scarabaeidae (Coleoptera) species

Meiotic chromosomes obtained from members of the coleopteran subfamilies Rutelinae and Dynastinae were studied using standard and silver nitrate staining, C-banding, base-specific fluorochromes and fluorescent in situ hybridization (FISH). The study presents detailed karyotipic descripitions of three Rutelinae species (Geniates borelli, Macraspis festiva and Pelidnota pallidipennis), and two Dynastinae species (Lygirus ebenus and Strategus surinamensis hirtus) with special emphasis on the distribution and variability of constitutive heterochromatin and the nucleolar organizer region (NOR). We found that for G. borelli, P. pallidipennis, L. ebenus and S. s hirtus the karyotype was 2n = 20 (9II + Xy p), with G. borelli, P. pallidipennis and L. ebenus showed meta-submetacentric chromosomes which gradually decreased in size. For Macraspis festiva the karyotype was 2n = 18 (8II + Xy p). In L. ebenus we found that the NOR was located on an autosome, but in the other four species it occurred on the sex bivalents. In all five species the constitutive heterochromatin (CH) was predominantly pericentromeric while the X chromosomes were almost completely heterochomatic, although CMA3/DA/DAPI staining showed intra and interspecific variation in the bright fluorescence of the constitutive heterochromatin. The FISH technique showed rDNA sites on the X chromosome of the Rutelinae species.

Cytogenetics of Manihot esculenta Crantz (cassava) and eight related species.

Thirty-nine cultivars of cassava and eight related wild species of Manihot were analyzed in this work for number, morphology and size of chromosomes, prophase condensation pattern and the structure of the interphase nucleus. In four accessions, the chromosome size was measured and in some others, the number of secondary constrictions, meiotic behavior, C-band pattern, CMA/DAPI bands, nucleoli number and the location of 5S and 18S-5.8S-28S rDNA sites were also observed. All investigated accessions showed a similar karyotype with 2n = 36, small metacentric to submetacentric chromosomes. Two pairs of terminal secondary constrictions were observed in the chromosome complement of each accession except Manihot sp. 1, which presented two proximal secondary constrictions. The prophase chromosome condensation pattern was proximal and the interphase nuclei structure was areticulate to semi-reticulate. The meiosis, investigated in seven cultivars and four wild species, was regular, displaying 18 bivalents. C-banding revealed heterochromatin in 9 or 10 chromosomes. The analysis with fluorochromes frequently showed four chromosome pairs with a single CMA+ terminal or subterminal band and a few other chromosomes with DAPI+ unstable bands. Six 45S rDNA sites were revealed by FISH, which seemed to colocalize with six CMA+ bands. Only one chromosome pair presented a 5S rDNA site. The maximum nucleoli number observed per nucleus was also six. These data suggest that all Manihot species present a very similar chromosome complement.