Capsicum (Solanaceae), native to the tropical and temperate Americas, comprises the well-known sweet and hot chili peppers and several wild species. So far, only partial taxonomic and phylogenetic ...analyses have been done for the genus. Here, the phylogenetic relationships between nearly all taxa of Capsicum were explored to test the monophyly of the genus and to obtain a better knowledge of species relationships, diversification and expansion.
Thirty-four of approximately 35 Capsicum species were sampled. Maximum parsimony and Bayesian inference analyses were performed using two plastid markers (matK and psbA-trnH) and one single-copy nuclear gene (waxy). The evolutionary changes of nine key features were reconstructed following the parsimony ancestral states method. Ancestral areas were reconstructed through a Bayesian Markov chain Monte Carlo analysis.
Capsicum forms a monophyletic clade, with Lycianthes as a sister group, following both phylogenetic approaches. Eleven well-supported clades (four of them monotypic) can be recognized within Capsicum, although some interspecific relationships need further analysis. A few features are useful to characterize different clades (e.g. fruit anatomy, chromosome base number), whereas some others are highly homoplastic (e.g. seed colour). The origin of Capsicum is postulated in an area along the Andes of western to north-western South America. The expansion of the genus has followed a clockwise direction around the Amazon basin, towards central and south-eastern Brazil, then back to western South America, and finally northwards to Central America.
New insights are provided regarding interspecific relationships, character evolution, and geographical origin and expansion of Capsicum A clearly distinct early-diverging clade can be distinguished, centred in western-north-western South America. Subsequent rapid speciation has led to the origin of the remaining clades. The diversification of Capsicum has culminated in the origin of the main cultivated species in several regions of South to Central America.
Arachis hypogaea is a natural, well-established allotetraploid (AABB) with 2n = 40. However, researchers disagree on the diploid genome donor species and on whether peanut originated by a single or ...multiple events of polyploidization. Here we provide evidence on the genetic origin of peanut and on the involved wild relatives using double GISH (genomic in situ hybridization). Seven wild diploid species (2n = 20), harboring either the A or B genome, were tested. Of all genomic DNA probe combinations assayed, A. duranensis (A genome) and A. ipaensis (B genome) appeared to be the best candidates for the genome donors because they yielded the most intense and uniform hybridization pattern when tested against the corresponding chromosome subsets of A. hypogaea. A similar GISH pattern was observed for all varieties of the cultigen and also for A. monticola. These results suggest that all presently known subspecies and varieties of A. hypogaea have arisen from a unique allotetraploid plant population, or alternatively, from different allotetraploid populations that originated from the same two diploid species. Furthermore, the bulk of the data demonstrated a close genomic relationship between both tetraploids and strongly supports the hypothesis that A. monticola is the immediate wild antecessor of A. hypogaea.
Chromosome number and position of rDNA were studied in 12 wild and cultivated species of the genus Capsicum with chromosome numbers x = 12 and x = 13 (22 samples). For the first time in these ...species, the 5S and 45S rRNA loci were localized and physically mapped using two-color fluorescence in situ hybridization and AgNOR banding. We focused on the comparison of the results obtained with both methods with the aim of accurately revealing the real functional rRNA genes. The analyzes were based on a previous work that reported that the 18S–5.8S–25S loci mostly coincide with GC-rich heterochromatic regions and likely have given rise to satellite DNAs, which are not active genes. These data show the variability of rDNA within karyotypes of the genus Capsicum, providing anchor points for (comparative) genetic maps. In addition, the obtained information might be useful for studies on evolution of repetitive DNA.
Triple staining with the fluorochromes chromomycin A3, distamycin A and 4′-6-diamidino-2-phenylindole (CMA/DA/DAPI) was applied to somatic metaphases and interphase nuclei of 11 taxa of wild chili ...peppers (
Capsicum
), with 2
n
= 2
x
= 24 (
C. annuum
var.
glabriusculum
,
C. cardenasii
,
C. chacoense
,
C. flexuosum
,
C. galapagoense
,
C. eximium
,
C. praetermissum
and
C. tovarii
) and 2
n
= 2
x
= 26 (
C. recurvatum
,
C. rhomboideum
and
C. villosum
) to analyse heterochromatin type, amount and distribution in wild members of this genus. Heterochromatic banding patterns allowed the identification of all the taxa examined and contributed to their taxonomic grouping. GC-rich heterochromatin (CMA+/DAPI−) was typical in all taxa; only
C. praetermissum
possessed also AT-rich (CMA−/DAPI+) and mixed GC- and AT-rich (CMA+/DAPI+) bands. Heterochromatin amount (expressed as % of karyotype length) ranged between 1.72 (
C. chacoense
) and 16.82 (
C. flexuosum
) and was positively correlated with karyotype length in most of the taxa examined. Heterochromatin located mainly at terminal position of chromosomes but intercalary position prevailed in
C. flexuosum
. Nucleolus organizer regions (NOR)-associated GC-rich heterochromatin was exclusively terminal and included the distal macrosatellite and a small portion on the corresponding arm. In all the taxa analysed, an equilocal heterochromatin distribution in non-homologous chromosomes of karyotype was observed, suggesting concerted evolution of heterochromatin dispersion in
Capsicum
.
Fluorescent chromosome banding and measurements of nuclear DNA content by image cytometry of Feulgen-stained cells were performed in one sample each of eight diploid (2n = 24) species of Solanum: S. ...endoadenium, S. argentinum, S. pseudocapsicum, S. atropurpureum, S. elaeagnifolium, S. sisymbriifolium, S. chenopodioides, and S. palustre. The species studied could be distinguished by heterochromatin amount, banding patterns, and genome size. They exhibited only GC-rich heterochromatin and showed a comparatively low heterochromatin amount (expressed as percentage of haplotype karyotype length), ranging from2.10 in S. argentinum to 8.37 in S. chenopodioides. Genome size displayed significant variation between species, with 1C-values ranging from 0.75 pg (735 Mbp) in S. palustre to 1.79 pg (1,754 Mbp) in S. sisymbriifolium. No significant correlation between genome size and heterochromatin amount was observed, but intrachromosomal asymmetry index (A₁) was negative and significantly correlated with heterochromatin amount. DNA content was positively and significantly correlated with karyotype length. DNA C-value distribution in the genus as well as karyotype affinities and relationships between species are discussed in relation to different infrageneric classifications of Solanum.
Flow cytometric measurements of nuclear DNA content were performed using ethidium bromide as the DNA stain (internal standard, Hordeum vulgare ‘Ditta’, 1C = 5·063 pg) in 25 samples belonging to nine ...diploid species and four varieties of Capsicum: C. chacoense, C. parvifolium, C. frutescens, C. chinense, C. annuum var. annuum, C. baccatum var. baccatum, C. baccatum var. pendulum, C. baccatum var. umbilicatum, C. eximium and C. pubescens, all with 2n = 24, and C. campylopodium with 2n = 26. In addition, one sample each of C. annuum var. annuum and C. pubescens were also analysed using Feulgen densitometry (standard, Allium cepa ‘Stuttgarter Riesen’, 1C = 16·75 pg). Both staining methods resulted in very similar relative values. Genome size displays significant variation between but not within species (except in C. campylopodium), and contributes to their taxonomic grouping. 1C‐values range from 3·34–3·43 pg (3273–3361 Mbp) in C. chacoense and the C. annuum complex to 4·53–5·77 pg (4439–5655 Mbp) in C. campylopodium and C. parvifolium. The data obtained support conclusions on phylogenetic relationships in the genus derived from karyotype analyses using chromosome banding approaches. In Capsicum, constitutive heterochromatin amount is correlated with genome size, except in C. parvifolium, and is regarded as an additive genomic component.
The 5S and the 18S-25S rRNA genes were physically mapped by fluorescent in situ hybridization (FISH) in all botanical varieties of cultivated peanut Arachis hypogaea {2n = 4x = 40), in the wild ...tetraploid A. monticola, and in seven wild diploid species considered as putative ancestors of the tetraploids. A detailed karyotype analysis including the FISH signals and the heterochromatic bands was carried out. Molecular cytogenetic landmarks are provided for the construction of a FISH-based karyotype in Arachis species. The size, number, and chromosome position of FISH signals and heterochromatic bands are similar in all A. hypogaea varieties and A. monticola, but vary among the diploid species. Genome constitution of the species is discussed and several chromosome homeologies are established. The bulk of the chromosome markers mapped, together with data on geographical distribution of the taxa, suggest that peanut originated upon domestication of A. monticola and evidence that the diploids A. duranensis and A. ipaensis are the most probable ancestors of both tetraploid species. Allopolyploidy could have arisen by a single event or, if by multiple events, always from the same diploid species.
A total of 106 samples taken from natural Argentinean populations of the weedy Solanum elaeagnifolium (subgenus Leptostemonum) were studied cytologically to understand the impact of the different ...ploidy levels in its distribution and origin. Classical Feulgen staining was employed to determine mitotic chromosome numbers in all samples. 2C nuclear DNA content was determined by means of PI flow cytometry in eight samples of different ploidy levels. Principal component analysis and GIS tools were employed to compare altitude, annual precipitation and annual mean temperature among accessions. Three cytotypes were found: diploid (2n = 24) which is widespread, tetraploid (2n = 48) centered in western and southern Argentina, and hexaploid (2n = 72) which predominates in central Argentina extending as well to the east. The annual precipitation is significantly different between tetraploids and hexaploids. Cx-values ranged from 1.231 to 1.275 pg, with statistical differences (of about 24.5–50.9 Mbp, p ≤ 0.05) among accessions. Diploids are the most widespread cytotype and have adapted to a number of very different habitats. Tetraploids live in arid or semi-arid regions with a mean annual rainfall less than 500 mm. Hexaploids are successful in colonizing wetter areas, where no tetraploids were found. Thus, the distribution of cytotypes may be associated with habitat differences, particularly soil moisture. The observed cytotype pattern and the differences in DNA content suggest multiple places of origin for the polyploidy of S. elaeagnifolium in Argentina.
The genus Cephalanthera is an excellent plant group for karyotype evolution studies because it exhibits a dysploid series and bimodal karyotypes. With the aim of understanding their chromosomal and ...phylogenetic relationships, rRNA genes and the Arabidopsis-type telomeric sequence were mapped by fluorescence in-situ hybridization (FISH), and the rDNA intergenic spacer (ITS) was sequenced for the first time in three European species: C. longifolia (2n = 4x = 32), C. damasonium (2n = 4x = 36) and C. rubra (2n = 4x = 44). One 45S and three 5S rDNA sites are observed in C. longifolia, one 45S and two 5S sites in C. damasonium, and two 45S and one 5S site in C. rubra. Telomeric signals were observed at every chromosome end in all three species and C. damasonium also displays interstitial signals on three chromosome pairs. In agreement with chromosome data, molecular analyses support C. longifolia and C. damasonium as closely related taxa, while C. rubra stands apart. Possible pathways of karyotype evolution are discussed in reference to a previous hypothesis. The results indicate that complex chromosomal rearrangements, possibly involving Robertsonian fusions and fissions, loss of telomeric repeats, gain or loss of rDNA sites and other heterochromatic sequences and inversions, may have contributed to generating the present-day karyotypes.
The primary and secondary structures of the intergenic spacer (IGS) between the 3′-end of 25S ribosomal RNA (rRNA) gene and the 5′-end of 18S rRNA gene are described for the cultivated chili pepper ...Capsicum pubescens. The recognized functional IGS is 2,078 bp in length. According to nucleotide base composition, regulatory elements, and conserved and repeated sequences the IGS can be divided into seven structural regions (SRI–VII). SRI comprises three copies of GAGGTTTTT-like motif, a probable transcription termination site in Solanaceae. At 3′-end, there are 21 bp matching the 18S rDNA. SRII is formed by 47 repeats of CACCATGG-like motif, the shortest repetitive region found in plant rDNA to date. SRIII is highly AT-rich, preceding SRIV, a highly conserved region in Solanaceae containing the transcription initiation site (TIS) TATATAAGGGGGG. The external transcribed spacer (ETS) is 966 bp in length. SRV-VII, downstream of the TIS, possesses eight inverted repeats, and three predicted stem-loops show pre-micro RNA (miRNA)-like structural features. Intragenomic variation is presented, and data are compared with characterized Solanaceae 25S–18S rDNA IGS.
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