Cyto-genetical investigations in some common cucurbits, with special reference to fragmentation of chromosomes as a physical basis of speciation.
TL;DR: Are sex chromosomes in higher pl,~nt~ nucleologenic?
Abstract: Introduction . M~t~rial and methods 0 bservations: Cucumis a~giz,u~ . Cucumis Memo Trichoaanth~ diolca Luffa aegyp~i~c,a . Luffa a~u~an~u~a . 6'o~iuia indica Beuincasa cerifera M~,mrdica cllarantia Cucurbita ~r~aarima Polysomaty Discussion (i) Numerica! correlation between m a~m um number ofnucleoli, sat~llltes and secondary constrictions (ii) Maximum number of nucleo]i ,lnd nucleolar constrictions of chromosomes witah reference to polyplcidy and aneuploidy . . . {iii) Variation of chromosome number in Cucm.bitaceac and R~. cytogsnetic interpretation (iv} Are sex chromosomes in higher pl,~nt~ nucleologenic? . Summary P, efsrsnces P A G ~
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TL;DR: The authors of this study assume that the novel cucumber reference genes determined will enable better normalization and quantification of transcript levels in future expression studies on cucumber plants.
Abstract: It has been shown that genes considered to be valid reference genes using semi-quantitative techniques (e.g. northern blot) appear to be less reliable when highly sensitive real-time PCR (qPCR) or microarrays are used. Therefore, the validation of expression stability of reference genes has become an important component of any study using such types of assay. No reference genes have been validated for expression studies of cucumber genes to date. Since the genome of this widely cultivated crop has been recently sequenced, the availability of suitable reference genes for expression analyses of the new cucumber genes is urgently required. For the purpose of normalization in studying expression of cucumber target genes, the stability of twelve reference genes in different cucumber tissues and under various stresses and growth regulators were determined in this study. These included commonly used cucumber reference genes, such as actin, EF, cyclophilin, ubiquitin and tubulin and the newly identified candidates for reference genes that encode clathrin adaptor complex subunit (CACS), F-box protein, PPA2 activator (tonoplast intrinsic protein, TIP41), mitosis protein (YSL8), protein phosphatase 2 (PDF2), helicase (HEL) and protein homolog of At4g33380. Analyses of quantitative real-time PCR data by three commonly used Excel-based applets, BestKeeper, geNorm and NormFinder, confirmed that expression stability of reference genes depends on the experimental parameters. In addition, they revealed that, except for EF, the most stable cucumber genes included mainly the new reference genes: CACS, F-box and TIP41, whereas the commonly used internal controls demonstrated various (actin, cyclophilin, ubiquitin) or much lower stability (tubulin). Hence, the authors of this study assume that the novel cucumber reference genes will enable better normalization and quantification of transcript levels in future expression studies on cucumber plants.
141 citations
Cites background from "Cyto-genetical investigations in so..."
...Biochemical, physiological and cytogenetic studies of this plant have been carried out for several decades (Bhaduri and Bose 1947; Burzyński et al. 2005; Chen et al. 1998; Janicka-Russak et al. 2008; Koo et al. 2002; Migocka and Klobus 2007; Ramachandran and Seshadri 1986), whereas the analysis of…...
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01 Jan 1993
TL;DR: The use of this vegetable is highlighted and its cytology, genetics, germplasm resources, and reproductive biology are reviewed and techniques applicable to the improvement of cucumber are described.
Abstract: Publisher Summary Cucumber, Cucumis sativus L., is a member of the Cucurbitaceae, which comprises 90 genera and 750 species. It is one of the oldest cultivated vegetable crops and is cultivated in nearly all countries of temperature zones. It is a thermophilic and frost-susceptible plant species, growing best at temperatures above 20 °C. This chapter highlights the use of this vegetable and reviews its cytology, genetics, germplasm resources, and reproductive biology. The taste and demands of the consumer varies according to country. Special varieties must be bred that set fruit under suboptimal temperature conditions. The demands of the processing industry concerning outer appearance—fruit shape, size, and color—also varies depending on the preservation process and the corresponding country. Therefore, cucumber breeders must consider several different breeding aims. General breeding objectives in cucumber are resistance to diseases and animal pests, maintenance of resistance in existing varieties, fruit quality, and fruit yield. Additionally, breeding aims such as parthenocarpy, constancy of femaleness, germination, and fruit set at suboptimum temperatures may be of importance in special breeding programs. Unlike many other plant species, there are different sex types in cucumber, which are of different value in breeding and concerning yield potential. By using sex inheritance and influencing sex expression, the breeding methods of self-pollinated and open-pollinated plants can be applied to cucumber. Thus, the cucumber breeder needs complete knowledge of sex inheritance and of potential ways of influencing sex expression. The chapter provides an overview of the selection of cucumber breeding methods and these methods. There have been several reports on the possibility of applying in vitro techniques in plant breeding of cucumber. The chapter describes techniques that are applicable to the improvement of cucumber.
128 citations
TL;DR: It is shown that balancing selection is common under biologically plausible conditions and that sex differences in selection or sex-by-genotype effects of mutations can each increase opportunities for balancing selection.
Abstract: How common is balancing selection, and what fraction of phenotypic variance is attributable to balanced polymorphisms? Despite decades of research, answers to these questions remain elusive. Moreover, there is no clear theoretical prediction about the frequency with which balancing selection is expected to arise within a population. Here, we use an extension of Fisher’s geometric model of adaptation to predict the probability of balancing selection in a population with separate sexes, wherein polymorphism is potentially maintained by two forms of balancing selection: (1) heterozygote advantage, where heterozygous individuals at a locus have higher fitness than homozygous individuals, and (2) sexually antagonistic selection (a.k.a. intralocus sexual conflict), where the fitness of each sex is maximized by different genotypes at a locus. We show that balancing selection is common under biologically plausible conditions and that sex differences in selection or sex-by-genotype effects of mutations can each increase opportunities for balancing selection. Although heterozygote advantage and sexual antagonism represent alternative mechanisms for maintaining polymorphism, they mutually exist along a balancing selection continuum that depends on population and sex-specific parameters of selection and mutation. Sexual antagonism is the dominant mode of balancing selection across most of this continuum.
107 citations
TL;DR: A fine-scale understanding of the mechanisms of dysploid chromosome reduction that has not been achieved previously is allowed to be achieved.
Abstract: †These authors contributed equally to this work. SUMMARY In the large Cucurbitaceae genus Cucumis, cucumber (C. sativus) is the only species with 2n = 2x = 14 chromosomes. The majority of the remaining species, including melon (C. melo) and the sister species of cucumber, C. hystrix, have 2n = 2x = 24 chromosomes, implying a reduction from n = 12 to n = 7. To understand the underlying mechanisms, we investigated chromosome synteny among cucumber, C. hystrix and melon using integrated and complementary approaches. We identified 14 inversions and a C. hystrix lineage-specific reciprocal inversion between C. hystrix and melon. The results reveal the location and orientation of 53 C. hystrix syntenic blocks on the seven cucumber chromosomes, and allow us to infer at least 59 chromosome rearrangement events that led to the seven cucumber chromosomes, including five fusions, four translocations, and 50 inversions. The 12 inferred chromosomes (AK1–AK12) of an ancestor similar to melon and C. hystrix had strikingly different evolutionary fates, with cucumber chromosome C1 apparently resulting from insertion of chromosome AK12 into the centromeric region of translocated AK2/AK8, cucumber chromosome C3 originating from a Robertsonian-like translocation between AK4 and AK6, and cucumber chromosome C5 originating from fusion of AK9 and AK10. Chromosomes C2, C4 and C6 were the result of complex reshuffling of syntenic blocks from three (AK3, AK5 and AK11), three (AK5, AK7 and AK8) and five (AK2, AK3, AK5, AK8 and AK11) ancestral chromosomes, respectively, through 33 fusion, translocation and inversion events. Previous results (Huang, S., Li, R., Zhang, Z. et al., 2009, Nat. Genet. 41, 1275‐1281; Li, D., Cuevas, H.E., Yang, L., Li, Y., Garcia-Mas, J., Zalapa, J., Staub, J.E., Luan, F., Reddy, U., He, X., Gong, Z., Weng, Y. 2011a, BMC Genomics, 12, 396) showing that cucumber C7 stayed largely intact during the entire evolution of Cucumis are supported. Results from this study allow a fine-scale understanding of the mechanisms of dysploid chromosome reduction that has not been achieved previously.
83 citations
Cites background from "Cyto-genetical investigations in so..."
...…to explain it: a fragmentation hypothesis that postulated de novo regeneration of centromeres from n = 7 to n = 12 (Kozhukhow, 1930; Whitaker, 1933; Bhaduri and Bose, 1947) and a fusion hypothesis that postulated that n = 7 was derived from n = 12 via unequal translocation or fusion of…...
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...The origin of the seven cucumber chromosomes has been a long-standing question, with opposite hypotheses being proposed to explain it: a fragmentation hypothesis that postulated de novo regeneration of centromeres from n = 7 to n = 12 (Kozhukhow, 1930; Whitaker, 1933; Bhaduri and Bose, 1947) and a fusion hypothesis that postulated that n = 7 was derived from n = 12 via unequal translocation or fusion of non-homologous chromosomes (Trivedi and Roy, 1970)....
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TL;DR: Both centromere activation and inactivation in cucurbit species were associated with a gain/loss of a large amount of pericentromeric heterochromatin.
Abstract: The centromere of an eukaryotic chromosome can move to a new position during evolution, which may result in a major alteration of the chromosome morphology and karyotype. This centromere repositioning phenomenon has been extensively documented in mammalian species and was implicated to play an important role in mammalian genome evolution. Here we report a centromere repositioning event in plant species. Comparative fluorescence in situ hybridization mapping using common sets of fosmid clones between two pairs of cucumber (Cucumis sativus L.) and melon (Cucumis melo L.) chromosomes revealed changes in centromere positions during evolution. Pachytene chromosome analysis revealed that the current centromeres of all four cucumber and melon chromosomes are associated with distinct pericentromeric heterochromatin. Interestingly, inactivation of a centromere in the original centromeric region was associated with a loss or erosion of its affixed pericentromeric heterochromatin. Thus, both centromere activation and inactivation in cucurbit species were associated with a gain/loss of a large amount of pericentromeric heterochromatin.
83 citations
Cites background from "Cyto-genetical investigations in so..."
...If the ancestor species for cucumber and melon contained 2n 14 chromosomes (24), then melon chromosome I (MeI) would be derived from a chromosomal fission event....
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References
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TL;DR: All genera except Haernanthus in the Amaryllidoideae may be concluded to have some karyotypical resemblances, when the karyotype alteration such as fusion, fragmentation, duplication, translocation, inversion, elimination and deficiency have been taken into consideration.
Abstract: (1) The karyotypes of nineteen genera in the Amaryllidoideae, namely Haerrzanthus (2n=16, 18), Grij inia (2n=77), Clivia (2n=44), Galanthus (2n=24, 25, 28, 48), Leucojum (2n=14, 22), Nerine (2n=22, 33), Amaryllis (2n=22), Zephyranthes (2n=12, 24, 38), Sternbergia (2n=22) Crirzum (2n=22, 33), Cyrtanthus (2n=22) Eucharis (2n=68), Hymenocallis (2n=46, 69), Narcissus (2n=14, 21, 22, 32), Paracratium (2n=44), Sprekelia (2n=ca. 117), Hippeastrum (2n=44), Habranthus (2n=21) and Lycoris (2n=27) have been analyzed from the point of karyotype alteration (cf. Table 1). Many genera such as Grinia, Clivia, Leucojum, Nerine, Amaryllis, Stervbergia, Crinum, Cyrtanthus, Pancratiurn, Hippeastrunz, Habranthus and Lycoris have the 11-series of chromo-somes, in the ether word 11 is their basic number of chromosomes which indicates the intimate relationship existing between these karyotypes. More striking is the fact that various karyotypes be-longing to the same genus, for instance Leucojutm (b=7, 11), have been explicitly explained by the dislocation hypothesis of Navashin (1932). By further reference to this hypothesis it may be possible to suggest the derivaticn of karyotypes in other genera.(2) The karyotypes of Hymenocallis (2n=46, 69) and Eucharis (2n=68) clearly indicate their derivation from the 11-series by the duplication of chromosomes and the secondary balance. The similar secondary polyploid appeared in Zephyranthes (b=6), i.e., Z. candicla (2n=38). All genera except Haernanthus in the Amaryllidoideae may be concluded to have some karyotypical resemblances, when the karyotype alteration such as fusion, fragmentation, duplication, translocation, inversion, elimination and deficiency have been taken into consideration. The karyotypes of Haemanthus resemble those of Scilla in the Liliaceae or Alstroemeria in the Hypoxidoideae.(3) The karyotypes of five genera in the Agavoideae, namely Bravoa, Polianthes, Agave, Fourcroya, and Beschorneria are similar (so-called the Yucca-Agave karyotype) (5 long and 25 short chromo-somes) (cf. Table 2). The karyotype of Dorjanthes (4 long and 44 short chromosomes) is different from the Yucca-Agave type, but some similarities are suggested, although difference in chromosome sizes can clearly be detected. The karyotypes of the Agavoideae are generally speaking different from other ones in the Amaryllidaceae and rather resemble those of Yuccae in the Liliaceae.(4) The karyotypes of Alstroenteria (2n=11) and Bornalia (2n=18) in the Hypoxidoideae are similar to those of Haemanthus (2n=16), especially in respect to the SAT-chromosomes.(5) The hypothesis of the SAT-chromosome has been adopted in the present analysis of karyotypes in the Amaryllidaceae and has brought about successful results. Various hypotheses of karyotype alteration were discussed and such karyotype alterations are con-cluded to be genotypically controlled (cf. Levitskij 1937). The genotypic control of karyotype alteration and the secondary balance seem to play an important role in the process cf evolution.(6) The relation between the nucleoli and the SAT-chromosomes was discussed and the hypothesis of the SAT-chromosome was extended to reconcile it with the conception of the nucleolar chromosome. The presence of the SAT-chromosome was emphasized by the observation of satellites or secondary constrictions in many species which had usually been overlooked cr neglected by previous investigators.The writer wishes to express his thanks to Ass. Prof. Y. Sinoto under whose direction this investigation has been carried out.
89 citations
TL;DR: The genera Trigczm~, _degi~ol:a and Secede, and along with them 0~'~jz¢ have been cytologically examined and are divided into three groups based on their chromosome number, sterility relationships, taxonomic differences, economic va.lue, and resistance to rusts.
Abstract: ]BECAUSE of the economic importance of many of the cereals, ~heir cyto]ogical sad genetiea] study has been a subject of prime importance practically a]l over the world. Aase (1935) has re,dewed the ey-go]ogJcal data of the cereals commonly spoken of as ;'small grains\", .w/we#t, ~'~/e, ba~'Ze F and o~ts. Along with wheat the near ly related wild grasses i e g { b p s , Ag~'o2y~'o~'~ and Hay~zc~ldic~ have also been discussed. I n the present paper oMy the genera Trigczm~, _degi~ol:a and Secede, and along with them 0~'~jz¢ have been cytologically examined. The %vZologieally s tudied species of the geaaus T.rigcum are dixdded in to three groups: e inkorn (2~=14) , cromer (29z=28) and vulgare group (2~, =~2), based on their chromosome number, sterility relationships, taxonomic differences, economic va.lue, and resistance to rusts. The plants belm?ging to the first group are of least economic importance but are rust resistant, those of the second group are of only little economic importance but many are rust resistant., and those of the third group, to
88 citations
85 citations
TL;DR: From the secondary association of chromosomes in three species the primary basic number for the genus has been inferred to be five, supported by the chromosome numbers of some related genera in which the basic number five has been retained for polyploidy.
Abstract: The cytological behaviour of three interspecific hybrids and twelve species ofBrassica is described and the following are the chief results obtained:
1.
The pairing of chromosomes in the F1 crossB. juncea Coss. (2n = 36) XB. campestris L. var.sarson Prain (2n = 20) takes place according to the Drosera scheme. With the exception of one cell, which showed 1iv+9II + 6I, all the rest showed 10II + 8I. From this and other evidence the amphidiploid origin ofB. juncea as a hybrid betweenB. campestris andB. nigra has been proved.
2.
In the crossB. Tournefortii Gouan (2n = 20) xB. trilocularis H.f.T. (2n = 20) the pairing of chromosomes is very variable. Nuclei with total lack of pairing to those showing a quadrivalent besides 1–3 bivalents were observed. The whole meiotic process in the hybrid is very irregular, resulting in the formation of dyads, monads and tryads to the extent of 25, 8 and 5%, respectively.
3.
The conjugation of chromosomes in the hybridB. trilocularis H.f.T. (2n = 20) xB. rapa L. (2n = 20) is complete, 10II being invariably formed at diakinesis and metaphase I. Non-disjunction of a bivalent was frequently observed at anaphase I. But for this irregularity the whole meiotic process is quite regular.
4.
B. sinapistrum Boiss. has 2n = 18,B. Tournefortii Gouan 2n = 20,B. monensis Huds. 2n=24 andB. rugosa 2n=38 chromosomes.
5.
Somatic chromosomes of nine species were examined, with special reference to the number of satellites and muceloli. A complete correspondence between the two has been found.
6.
WhereasB. nigra Koch, which has the lowest chromosome number in the genus (2n=16) shows four satellites and four nucleoli,B. oleracea L. (2n = 18),B. rapa L. (2n = 20),B. campestris L. (2n = 20),B. trilocularis (2n = 20) andB. Tournefortii (2n = 2) show only one pair each. This suggests that the latter five species have lost the extra pair of satellites by mutation during the course of evolution. The presence of six satellites and six nucleoli inB. juncea and four nucleoli inB. napus and.B. rugosa has been correlated with their amphidiploid nature, and is additional proof of this.
7.
Other interesting features in somatic mitosis, such as somatic pairing, sporadic aberrations in chromosome numbers and formation of chromatin bridges, have been described.
8.
From the secondary association of chromosomes in three species the primary basic number for the genus has been inferred to be five. This conclusion is supported by the chromosome numbers of some related genera in which the basic number five has been retained for polyploidy. In certain other genera the hexaploid number thirty is basic, and some species have become tetraploid on this basis. Some other evidence has also been adduced to show that all the monogenomic species ofBrassica have a common origin.
9.
WhileB. campeslris, B. trilocularis, B. Tournefortii andB. rapa show exclusively bivalent formation at meiosis,B. juncea, B. sinapistrum andB. monensis show occasionally a quadrivalent.B. nigra andB. Wrightii show in addition higher multivalents. The probable reasons for the formation of multivalents in each of this species have been discussed.
10.
Presence of relatively inverted segments of chromosomes has Journ. of Genetics Sl been inferred in some species from the chromatin bridges formed at meiosis.
11.
The role played by gene mutations, structurai changes of chromosomes and hybridization in species formation inBrassica has been discussed. Of these hybridization has played the most important part, as amphidiploidy has frequently occurred in the genus.
83 citations