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Diagram representing the partial alignment of 5S rDNA sequences of Vigna (AP017185.1), Lilium (KM117262.1), Arabidopsis (AY130622.1), Cestrum aurantiacum × C. parqui (AY135508.1), Cestrum psittacinum (AF495752.1), 5SplantCestrum, 5SUPCestrum and 5SUP-BChrom, for location of gene coding and NTS regions. Note the two internal deletions in the 5S rDNA gene coding of B chromosome sequence (arrow).
Source publication
Species of Cestrum (Linnaeus, 1753) have shown large diversity in the accumulation and distribution of repetitive DNA families, and B chromosomes have been described in seven species. Some types of repetitive DNA were identified in A and B chromosomes in species of this plant group, such as AT-rich SSR, 35S and 5S rDNA, C-Giemsa and C-CMA/DAPI band...
Citations
... Distal chromosome regions are hotspots of repetitive families, in addition to telomeres (Baird 2018). The best example may be the distal location of 35S rDNA sites found in most plant groups, including those belonging to Solanum (Dong et al. 2000), Capsicum (Moscone et al. 1995;Scaldaferro et al. 2016), Nicotiana (Lim et al. 2000), and Cestrum (Vanzela et al. 2017). Distally located satellite sequences were also observed in Allium, Deschampsia, and Passiflora (González et al. 2018;Pamponét et al. 2019). ...
Chili peppers (Solanaceae family) have great commercial value. They are commercialized in natura and used as spices and for ornamental and medicinal purposes. Although three whole genomes have been published, limited information about satellite DNA sequences, their composition, and genomic distribution has been provided. Here, we exploited the noncoding repetitive fraction, represented by satellite sequences, that tends to accumulate in blocks along chromosomes, especially near the chromosome ends of peppers. Two satellite DNA sequences were identified (CDR-1 and CDR-2), characterized and mapped in silico in three Capsicum genomes (C. annuum, C. chinense, and C. baccatum) using data from the published high-coverage sequencing and repeats finding bioinformatic tools. Localization using FISH in the chromosomes of these species and in two others (C. frutescens and C. chacoense), totaling five species, showed signals adjacent to the rDNA sites. A sequence comparison with existing Solanaceae repeats showed that CDR-1 and CDR-2 have different origins but without homology to rDNA sequences. Satellites occupied subterminal chromosomal regions, sometimes collocated with or adjacent to 35S rDNA sequences. Our results expand knowledge about the diversity of subterminal regions of Capsicum chromosomes, showing different amounts and distributions within and between karyotypes. In addition, these sequences may be useful for future phylogenetic studies.
... Chromosome painting of seven B chromosomes in two fish species belonging to the genus Astyanax with 18S ribosomal DNA (rDNA), H1 histone genes and As51 satellite DNA (AC) 15 microsatellite-based probes has shown that all Bs shared homologous DNA sequences not only amongst them but also with a variable number of A chromosomes in each species indicating a common origin for all seven Bs analysed (Duílio et al., 2016). The B chromosome in Cestrum strigilatum differs from the B chromosome of the other six species as it lacks the 5S rDNA sequence, which either might have been lost during B chromosome differentiation in this species or the B chromosome has evolved independently in this species (Vanzela et al., 2017). ...
Investigated for more than a century now, B chromosomes (Bs) research has come a long way from Bs being considered parasitic or neutral to becoming unselfish and bringing benefits to their hosts. B chromosomes exist as accessory chromosomes along with the standard A chromosomes (As) across eukaryotic taxa. Represented singly or in multiple copies, B chromosomes are largely heterochromatic but also contain euchromatic and organellar segments. Although B chromosomes are derived entities, they follow their species-specific evolutionary pattern. B chromosomes fail to pair with the standard chromosomes during meiosis and vary in their number, size, composition and structure across taxa and ensure their successful transmission through non-mendelian mechanisms like mitotic, pre-meiotic, meiotic or post-meiotic drives, unique non-disjunction, self-pairing or even imparting benefits to the host when they lack drive. B chromosomes have been associated with cellular processes like sex determination, pathogenicity, resistance to pathogens, phenotypic effects, and differential gene expression. With the advancements in B-omics research, novel insights have been gleaned on their functions, some of which have been associated with the regulation of gene expression of A chromosomes through increased expression of miRNAs or differential expression of transposable elements located on them. The next-generation sequencing and emerging technologies will further likely unravel the cellular, molecular and functional behaviour of these enigmatic entities. Amidst the extensive fluidity shown by B chromosomes in their structural and functional attributes, we perceive that the existence and survival of B chromosomes in the populations most likely seem to be a trade-off between the drive efficiency and adaptive significance versus their adverse effects on reproduction.
... and C. nocturnum L. [17,18]. Furthermore, it is known that the B chromosomes occur in seven species of Cestrum, with variation in the repetitive DNA composition (retrotransposons, simple sequence repeats, rDNA and heterochromatic bands) [18][19][20][21][22][23]. ...
... Considering that karyotypes of Cestrum are relatively symmetrical and with the same 2n [15] and that each chromosome could represent approximately 12.5% of the set, it is reasonable to suggest that variations in the DNA C-value occur due to changes in the repetitive fraction or by the presence of B chromosomes. Seven species of Cestrum exhibit B chromosomes [18][19][20][21][22][23][24], and of those, three (C. strigilatum, C. intermedium and C. axillare) were analyzed here. ...
... Non-LTR, transposons, and simple sequence repeats (SSRs) elements were less accumulated in these two genomes. Sequences of rDNA also varied between these two genomes, as previously reported [15,[20][21][22]24]. Although the lack of other genome sequencing makes it difficult to have a greater understanding of the dynamics of the repetitive DNA families, previous results of chromosome banding and FISH with repetitive probes have shown a diversity in the repetitive fraction in Cestrum, including the B chromosomes [15,17,20,23,24]. ...
Background
Cestrum species present large genomes (2 C = ~ 24 pg), a high occurrence of B chromosomes and great diversity in heterochromatin bands. Despite this diversity, karyotypes maintain the chromosome number 2n = 16 (except when they present B chromosomes), and a relative similarity in chromosome morphology and symmetry. To deepen our knowledge of the Cestrum genome composition, low-coverage sequencing data of C. strigilatum and C. elegans were compared, including cytogenomic analyses of seven species.
Methods and results
Bioinformatics analyses showed retrotransposons comprising more than 70% of the repetitive fraction, followed by DNA transposons (~ 17%), but FISH assays using retrotransposon probes revealed inconspicuous and scattered signals. The four satellite DNA families here analyzed represented approximately 2.48% of the C. strigilatum dataset, and these sequences were used as probes in FISH assays. Hybridization signals were colocalized with all AT- and GC-rich sequences associated with heterochromatin, including AT-rich Cold-Sensitive Regions (CSRs). Although satellite probes hybridized in almost all tested species, a satDNA family named CsSat49 was highlighted because it predominates in centromeric regions.
Conclusions
Data suggest that the satDNA fraction is conserved in the genus, although there is variation in the number of FISH signals between karyotypes. Except to the absence of FISH signals with probes CsSat1 and CsSat72 in two species, the other satellites occurred in species of different phylogenetic clades. Some satDNA sequences have been detected in the B chromosomes, indicating that they are rich in preexisting sequences in the chromosomes of the A complement. This comparative study provides an important advance in the knowledge on genome organization and heterochromatin composition in Cestrum, especially on the distribution of satellite fractions between species and their importance for the B chromosome composition.
... Five species of Cestrum presented B chromosomes with 35S and 5S rDNA sequences such as C. parqui × C. aurantiacum [52], C. nocturnum, C. euanthes, C. parqui [13,53], and C. axillare, similar to that described here. Two other species, C. strigilatum and C. intermedium, exhibited no rDNA sites on B chromosomes using FISH [12,54]. This can be a good opportunity for future studies on the accessory chromosome origin in perennial plants, such as Cestrum, as the B chromosome 1 3 maintains its size (~ 3 µm) and similar submetacentric form in all species. ...
The 35S and 5S ribosomal DNA (rDNA) organized in thousands of copies in genomes, have been widely used in numerous comparative cytogenetic studies. Nevertheless, several questions related to the diversity and organization of regulatory motifs in 5S rDNA remain to be addressed. The 5S rDNA unit is composed of a conserved 120 bp length coding region and an intergenic spacer (IGS) containing potential regulatory motifs (Poly-T, AT-rich and GC-rich) differing in number, redundancy and position along the IGS. The Cestrum species (Solanaceae) have large genomes (about 10 pg/1C) and conserved 2n = 16 karyotypes. Strikingly, these genomes show high diversity of heterochromatin distribution, variability in 35S rDNA loci and the occurrence of B chromosomes. However, the 5S rDNA loci are highly conserved in the proximal region of chromosome 8. Comparison of seventy-one IGS sequences in plants revealed several conserved motifs with potential regulatory function. The AT- and GC-rich domains appeared highly conserved in Cestrum chromosomes. The 5S genic and the GC-rich IGS probe produced FISH signals in both A (pair 8) and B chromosomes. The GC-rich domain presented a strong potential for regulation because it may be associated with CpG islands organization, as well as to hairpin and loop organization. Another interesting aspect was the ability of AT- and GC-rich motifs to produce non-heterochromatic CMA/DAPI signals. While the length of the 5S rDNA IGS region varied in size between the Cestrum species, the individual sequence motifs seem to be conserved suggesting their regulatory function. The most striking feature was the conserved GC-rich domain in Cestrum, which is recognized as a signature trait of the proximal region of chromosome pair 8.
... In C. intermedium and C. strigilatum, besides C-Giemsa+/CMA+/DAPI+ bands [73], the Bs also display hybridization signals with the Gypsy-like retrotransposon probe but not with rDNA probes [73]. Some types of repetitive DNA were identified in A and B chromosomes in C. strigilatum and in species of this plant group, such as AT-rich SSR, 35S and 5S rDNA, C-Giemsa and C-CMA/DAPI bands and retrotransposons [77]. ...
B chromosomes are supernumerary chromosomes found in addition to the normal standard chromosomes (A chromosomes). B chromosomes are well known to accumulate several distinct types of repeated DNA elements. Although the evolution of B chromosomes has been the subject of numerous studies, the mechanisms of accumulation and evolution of repetitive sequences are not fully understood. Recently, new genomic approaches have shed light on the origin and accumulation of different classes of repetitive sequences in the process of B chromosome formation and evolution. Here we discuss the impact of repetitive sequences accumulation on the evolution of plant B chromosomes.
... In C. intermedium and C. strigilatum, besides C-Giemsa+/CMA+/DAPI+ bands [66], the Bs also display hybridization signals with the Gypsy-like retrotransposon probe but not with rDNA probes [66]. Some types of repetitive DNA were identified in A and B chromosomes in C. strigilatum and in species of this plant group, such as AT-rich SSR, 35S and 5S rDNA, C-Giemsa and C-CMA/DAPI bands and retrotransposons [70]. ...
B chromosomes are supernumerary chromosomes which are found in addition to the normal standard chromosomes (A chromosomes). B chromosomes are well known to accumulate several types of repeats. Although the evolution of B chromosomes has been subject of numerous studies, the mechanisms of accumulation and evolution of repetitive sequences is not fully understood. Recently, new genomic approaches have shed light on the origin and accumulation of different classes of repetitive sequences in the process of B chromosome formation and evolution. Here we discuss the impact of repetitive sequences accumulation on the evolution of plant B chromosomes.
The Cestrum genus is karyotypically exceptional in Solanaceae. It is characterised by a basic number x = 8, a large chromosomal and genomic size, complex heterochromatin patterns, B-chromosomes (Bs) with particular heterochromatin and distribution of 18–5.8–26S and 5S rDNA. Cestrum nocturnum L. has a diploid number of 2n = 16 plus a variable number of B-chromosomes. The aims of work was to analyse their numerical variation, structure and behaviour of C. nocturnum B-chromosomes by classical and molecular cytogenetics. The individuals analysed had 2n = 16 + 0−13 B-chromosomes. All B-chromosomes were metacentric and smaller than A-chromosomes. The number of B-chromosomes showed a great variability between and within individuals, thereby denoting the occurrence of events that promote mitotic and meiotic instability. Cytogenetic techniques made it possible to observe that B-chromosomes are rich in heterochromatin, probably with AT- and GC-rich regions. In addition, molecular techniques allowed to detect homologous sequences of transposable element conserved domains of Ty1-Copia and Ty3-Gypsy superfamilies. These sequences were located by FISH in all B-chromosomes and some A-chromosomes. Our results showed that repetitive DNA could play an important role in chromosomal evolution as well as in the stability of B-chromosomes in C. nocturnum.
