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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01 Jan 1939
8 citations
6 citations
TL;DR: A tentative suggestion is put forward to explain the autosomal position of Beaded as compared with the sex-linked nature ofPI andPII, which is suggested that as the result of translocation theX-chromosome in D. obscura has one arm, or part of one arm corresponding to part of the third chromosome inD. melanogaster.
Abstract: 1.
The behaviour of two modifiers inDrosophila obscura, m1, located in theX-chromosome at 13·7 units fromPI andm2, linked with orange in the third linkage group and located at 9·2 units from orange, is described.
2.
PII, an allelomorph of the previously described Pointed (PI) mutant, gives a similar but weaker effect upon the wing character to Pointed.
3.
The genem1, which has the effect of intensifying the character, gives a weaker effect withPII than withPI. The genem2, which reduces the variability of the character, similarly affectsPII less thanPI.
4.
It is suggested thatPI andPII inD. obscura are homologous withBd (Beaded) inD. melanogaster because of (a) the great similarity of the morphological expression of the two genes, and (b) the similarity of their behaviour in the presence of modifying factors.
5.
A tentative suggestion is put forward to explain the autosomal position of Beaded as compared with the sex-linked nature ofPI andPII. It is suggested that as the result of translocation theX-chromosome inD. obscura has one arm, or part of one arm, corresponding to part of the third chromosome inD. melanogaster. This hypothesis is supported by (a) the cytological differences in size and shape of theX-chromosomes inD. obscura andD. melanogaster, (b) by the position of the yellow-scute loci in the two species, (c) by the evidence from the hybrids between raceA andB ofD. obscura, and (d) the cytological observations of similar rearrangement of chromosome parts in many plants and inDrosophila melanogaster.
6 citations
6 citations