RESUMO
Naturally occurring genetic variation in plants can be very useful to dissect the complex regulation of primary metabolism as well as of physiological traits such as photosynthesis and photorespiration. The physiological and genetic mechanisms underlying natural variation in closely related species or accessions may provide important information that can be used to improve crop yield. In this chapter we describe in detail the use of a population of introgression lines (ILs), with the Solanum pennellii IL population as a study case, as a tool for the identification of genomic regions involved in the control of photosynthetic efficiency.
Assuntos
Regulação da Expressão Gênica de Plantas , Genes de Plantas , Variação Genética , Fotossíntese/genética , Característica Quantitativa Herdável , Solanum/genética , Dióxido de Carbono/análise , Dióxido de Carbono/metabolismo , Quimera , Clorofila/metabolismo , Clorofila A , Mapeamento Cromossômico , Cromossomos de Plantas/química , Cruzamentos Genéticos , Fluorescência , Marcadores Genéticos , Genótipo , Imagem Óptica/métodos , Oxigênio/análise , Oxigênio/metabolismo , Consumo de Oxigênio/genética , Fenótipo , Melhoramento Vegetal , Folhas de Planta/genética , Folhas de Planta/metabolismo , Locos de Características Quantitativas , Solanum/metabolismoRESUMO
White mold, caused by the fungus Sclerotinia sclerotiorum (Lib.) de Bary, is a major disease that limits common bean production and quality worldwide. The host-pathogen interaction is complex, with partial resistance in the host inherited as a quantitative trait with low to moderate heritability. Our objective was to identify meta-QTL conditioning partial resistance to white mold from individual QTL identified across multiple populations and environments. The physical positions for 37 individual QTL were identified across 14 recombinant inbred bi-parental populations (six new, three re-genotyped, and five from the literature). A meta-QTL analysis of the 37 QTL was conducted using the genetic linkage map of Stampede x Red Hawk population as the reference. The 37 QTL condensed into 17 named loci (12 previously named and five new) of which nine were defined as meta-QTL WM1.1, WM2.2, WM3.1, WM5.4, WM6.2, WM7.1, WM7.4, WM7.5, and WM8.3. The nine meta-QTL had confidence intervals ranging from 0.65 to 9.41 Mb. Candidate genes shown to express under S. sclerotiorum infection in other studies, including cell wall receptor kinase, COI1, ethylene responsive transcription factor, peroxidase, and MYB transcription factor, were found within the confidence interval for five of the meta-QTL. The nine meta-QTL are recommended as potential targets for MAS for partial resistance to white mold in common bean.
Assuntos
Ascomicetos/genética , Resistência à Doença/genética , Phaseolus/genética , Locos de Características Quantitativas , Mapeamento Cromossômico , Cromossomos de Plantas/química , Cromossomos de Plantas/genética , Ligação Genética , Genótipo , Peroxidase/genética , Peroxidase/metabolismo , Phaseolus/microbiologia , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Polimorfismo de Nucleotídeo Único , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
In this study, dynamic quantitative trait loci (QTL) were mapped in a recombinant inbred line (F2:4) population derived from a BF3109 x Q267 cross. This was done during the unconditional (4, 7, and 10 days) and conditional (0 to 4, 4 to 7, and 7 to 10 days) germination stages in sh2 sweet corn. The values of seedling dry weight, weight of mobilized seed reserve (WMSR), seed reserve depletion percentage (SRDP), seed reserve utilization efficiency (SRUE), and their heritability differed across the investigated stages. The heritabilities of these traits were lower at 7D/4D and 10D/7D compared with those at the 4- (4D/0D), 7- and 10-day (D) developmental stages. WMSR and SRDP were significantly negatively correlated with SRUE at the early stage. The unconditional QTL mapping can explain the accumulation of genetic effects of seed reserve utilization from the starting time, whereas the conditional QTL mapping can reveal genetic expression in the time intervals. Fifteen and fourteen additive QTLs were identified by the unconditional and conditional mapping, respectively. The number of additive QTLs and their effect values varied among the different stages. More additive QTLs were found at the later stage (7 to 10 days), based on the conditional mapping results. The identification of QTL mapping based on a combination of time-dependent measurements is important for a better understanding of the genetic bases of seed reserve utilization. It is also important for the improvement of relevant variety traits for subsequent sweet corn-breeding studies using marker-assisted selection.
Assuntos
Cromossomos de Plantas/química , Locos de Características Quantitativas , Plântula/genética , Sementes/genética , Zea mays/genética , Mapeamento Cromossômico , Cruzamentos Genéticos , Germinação , Fenótipo , Melhoramento Vegetal , Sementes/crescimento & desenvolvimento , Zea mays/crescimento & desenvolvimentoRESUMO
BACKGROUND: Long noncoding RNAs (lncRNAs) represent a class of RNA molecules that are implicated in regulation of gene expression in both mammals and plants. While much progress has been made in determining the biological functions of lncRNAs in mammals, the functional roles of lncRNAs in plants are still poorly understood. Specifically, the roles of long intergenic nocoding RNAs (lincRNAs) in plant defence responses are yet to be fully explored. RESULTS: In this study, we used strand-specific RNA sequencing to identify 1113 lincRNAs in potato (Solanum tuberosum) from stem tissues. The lincRNAs are expressed from all 12 potato chromosomes and generally smaller in size compared to protein-coding genes. Like in other plants, most potato lincRNAs possess single exons. A time-course RNA-seq analysis between a tolerant and a susceptible potato cultivar showed that 559 lincRNAs are responsive to Pectobacterium carotovorum subsp. brasiliense challenge compared to mock-inoculated controls. Moreover, coexpression analysis revealed that 17 of these lincRNAs are highly associated with 12 potato defence-related genes. CONCLUSIONS: Together, these results suggest that lincRNAs have potential functional roles in potato defence responses. Furthermore, this work provides the first library of potato lincRNAs and a set of novel lincRNAs implicated in potato defences against P. carotovorum subsp. brasiliense, a member of the soft rot Enterobacteriaceae phytopathogens.
Assuntos
Resistência à Doença/genética , Regulação da Expressão Gênica de Plantas , Interações Hospedeiro-Patógeno , Pectobacterium carotovorum/patogenicidade , RNA Longo não Codificante/genética , RNA de Plantas/genética , Solanum tuberosum/genética , Cromossomos de Plantas/química , Éxons , Biblioteca Gênica , Ontologia Genética , Anotação de Sequência Molecular , Pectobacterium carotovorum/crescimento & desenvolvimento , Doenças das Plantas/genética , Doenças das Plantas/imunologia , Doenças das Plantas/microbiologia , Imunidade Vegetal/genética , Caules de Planta/genética , Caules de Planta/imunologia , Caules de Planta/microbiologia , RNA Longo não Codificante/classificação , RNA Longo não Codificante/imunologia , RNA de Plantas/classificação , RNA de Plantas/imunologia , Solanum tuberosum/imunologia , Solanum tuberosum/microbiologiaRESUMO
Grain size is an important trait that directly influences rice yield. The qGL3 and GS3 genes are two putative regulators that play a role in grain size determination. A single rare nucleotide substitution (CâA) at position 1092 in exon 10 of qGL3 might be responsible for variations in grain size. However, little is known about the haplotype variations of qGL3 and their interactions with GS3 during the regulation of grain length and grain weight. In this study, qGL3 haplotype variations were examined in 61 Indica varieties, and the effects of qGL3 and GS3 on grain trait variation in 110 lines were evaluated. Six qGL3 haplotypes were identified, and qGL3-2 was a major haplotype in Indica varieties. Moreover, qGL3-6, a reported key single nucleotide polymorphism, was validated. Our results showed that the mutants qgl3 and gs3 (loss-of-function mutation types of qGL3 and GS3, respectively) had significant effects on grain length and grain weight. However, no significant effects associated with differences in the regulation of grain thickness were observed. The genetic effects of qgl3 on grain phenotypes were stronger than those of gs3. In addition to increased grain length, qgl3 had an evident role in grain width increases. In contrast, gs3 played an opposite role in grain width regulation. These results provided novel insights into grain size control and the functions of qgl3 and gs3 in rice yield improvement.
Assuntos
Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Haplótipos , Oryza/genética , Proteínas de Plantas/genética , Locos de Características Quantitativas , Característica Quantitativa Herdável , Alelos , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Cromossomos de Plantas/química , Grão Comestível , Epistasia Genética , Éxons , Mutação , Oryza/metabolismo , Fenótipo , Melhoramento Vegetal , Proteínas de Plantas/metabolismo , Polimorfismo de Nucleotídeo ÚnicoRESUMO
Simple sequence repeats (SSRs) are highly informative, polymorphic, and co-dominant Mendelian markers that provide an important genomic resource for genetic research. Recently, the use of large-scale transcriptome sequence has become a reliable and efficient approach for the identification and development of new EST-SSR markers. In this study, 8389 potential SSRs with a minimum of five repetitions for all motifs were identified from 121,210 unigenes. Gene ontology analysis indicated that the unigenes containing SSR loci participate in various biological processes of regulation, growth, development, metabolism, and apoptosis in wheat. As in many other plants, trinucleotide repeats were found to be the most abundant repeat units with a frequency of 62.33%. A subset of 300 EST-SSRs was randomly selected for the applicability of EST-SSRs to be evaluated. Of the 300 primer pairs tested, 177 (59%) yielded unambiguous PCR products among five wheat cultivars. Using the Chinese Spring nulli-tetrasomic line, 131 of the 177 EST-SSR primer pairs yielded products and 178 loci were found to be located on all the 21 wheat chromosomes. These findings suggest that the novel EST-SSR markers, as a basis for future genetic linkage and gene tagging analysis, are a valuable tool for genetic mapping, marker assisted selection, and comparative genome analysis.
Assuntos
Cromossomos de Plantas/química , Etiquetas de Sequências Expressas , Repetições de Microssatélites , Transcriptoma , Triticum/genética , Mapeamento Cromossômico , Primers do DNA/genética , Ontologia Genética , Ligação Genética , Loci Gênicos , Anotação de Sequência Molecular , Reação em Cadeia da Polimerase , Polimorfismo GenéticoRESUMO
Genetic improvement is the fundamental basis for improving nitrogen-use efficiency. A better understanding of genetic factors controlling nitrogen uptake and utilization is required for crop genetic improvement. In this study, we identified the quantitative trait loci (QTLs) associated with traits of nitrogen uptake and utilization by using the single-sequence repeat marker method and a recombinant inbred line (RIL) population derived from a super hybrid Xieyou9308. All the traits investigated were inherited quantitatively by continuous variation and showed normal distribution in phenotype with transgressive segregation in the RIL population. Most of the traits were significantly correlated with each other except for nitrogen absorption ability (NAA) with nitrogen harvest index (NHI) and NHI with agricultural nitrogen-absorption efficiency (ANAE). At logarithmic odds value of 2.3, total 13 candidate QTLs, including 4 for NAA, 2 for NHI, 2 for physiological nitrogen-use efficiency, 1 for agricultural nitrogen-use efficiency (ANUE), and 4 for ANAE, were detected and mapped on chromosomes 2, 3, 4, 5, 8, 9, 10, and 12. Significant pleiotropic effect or neighboring expression of QTLs was observed among traits. At position 64.8 cM on chromosome 4 near the marker RM5757, there was a QTL cluster of NAA, ANUE, and ANAE, and at chromosome 5 near the marker RM5968, there was a QTL cluster of NAA and ANUE. The QTL clusters might provide partial explanation and genetic mechanism for the observed correlations between nitrogen uptake and utilization efficiency traits and might form a basis for future breeding programs.
Assuntos
Quimera/genética , Fertilizantes/análise , Nitrogênio/metabolismo , Oryza/genética , Locos de Características Quantitativas , Transporte Biológico , Quimera/metabolismo , Mapeamento Cromossômico , Cromossomos de Plantas/química , Ligação Genética , Marcadores Genéticos , Pleiotropia Genética , Genótipo , Repetições de Microssatélites , Família Multigênica , Oryza/metabolismo , Fenótipo , Plantas Geneticamente ModificadasRESUMO
The low-light tolerance index was investigated in a set of 123 F2:3 lines during the seedling stage across 2 seasons, and the heredity of low-light tolerance was assessed via different ge-netic analysis methods. The results of the classical analysis showed that low-light tolerance is controlled by an additive-dominant poly-gene, and the polygenic inheritance rate of separate generations was >30%. In addition, 5 quantitative trait loci (QTLs) exhibited a low-light tolerance index across both seasons, including 2 QTLs (Llti1.1 and Llti1.2) on the 1st linkage group (variances of 6.0 and 9.5%) and 3 QTLs (Llti2.1, Llti2.1, and Llti2.1) on the 2nd linkage group (variances of 10.1-14.0%). The classical analysis method and QTL information on the heredity of low-light tolerance showed that it is controlled by several major genes and a mini-polygene. The results will facilitate the breeding of resistance to low-light stress in cucumber.
Assuntos
Adaptação Fisiológica/genética , Cucumis sativus/genética , Genes de Plantas , Herança Multifatorial , Locos de Características Quantitativas , Adaptação Fisiológica/efeitos da radiação , Mapeamento Cromossômico , Cromossomos de Plantas/química , Cucumis sativus/crescimento & desenvolvimento , Cucumis sativus/efeitos da radiação , Bases de Dados Genéticas , Ligação Genética , Luz , Fenótipo , Melhoramento Vegetal , Estações do Ano , PlântulaRESUMO
Cotton (Gossypium spp) is one of the most economically important crops that provide the world's most widely used natural fiber. Diseases such as Fusarium wilt and particularly Verticillium wilt seriously affect cotton production, and thus breeding for disease resistance is one of the most important goals of cotton breeding programs. Currently, potential exists to improve disease resistance in cultivated cotton. Increasing the understanding of the distribution, structure, and organization of genes or quantitative trait loci for disease resistance will help the breeders improve crop yield even in the event of disease. To facilitate the mapping of disease-resistance quantitative trait loci to achieve disease-resistant molecular breeding in cotton, it is necessary to develop polymorphic molecular markers. The objective of this study was to develop simple sequence repeat markers based on cotton expressed sequence tags for disease resistance. The efficacy of these simple sequence repeat markers, their polymorphisms, and cross-species transferability were evaluated. Their value was further investigated based on genetic diversity and evolution analysis. In this study, the unique sequences used to develop markers were compared with the G. arboretum and G. raimondii genome sequences to investigate their position, homology, and collinearity between G. arboretum and G. raimondii.
Assuntos
Cromossomos de Plantas/química , Resistência à Doença/genética , Gossypium/genética , Doenças das Plantas/genética , Polimorfismo Genético/imunologia , Locos de Características Quantitativas , Sequência de Bases , Evolução Biológica , Mapeamento Cromossômico , Resistência à Doença/imunologia , Fusarium/patogenicidade , Fusarium/fisiologia , Marcadores Genéticos , Gossypium/classificação , Gossypium/imunologia , Gossypium/microbiologia , Repetições de Microssatélites , Dados de Sequência Molecular , Filogenia , Melhoramento Vegetal , Doenças das Plantas/imunologia , Doenças das Plantas/microbiologia , Alinhamento de Sequência , Homologia de Sequência do Ácido Nucleico , Verticillium/patogenicidade , Verticillium/fisiologiaRESUMO
The DNA-binding one zinc finger (Dof) family is a classic plant-specific zinc-finger transcription factor family, which is involved in many important processes, including seed maturation and germination, plant growth and development, and light responses. Investigation of the Medicago truncatula genome revealed 42 putative Dof genes, each of which holds one Dof domain. These genes were classified into four groups based on phylogenetic analysis, which are similar to the groups reported for Arabidopsis and rice. Based on genome duplication analysis, it was found that the MtDof genes were distributed on all chromosomes and had expanded through tandem gene duplication and segmental duplication events. Two main duplication regions were identified, one from tandem duplication and another from segmental duplication. By analyzing high-throughput sequencing data from M. truncatula, we found that most of the MtDof genes showed specific expression patterns in different tissues. According to cis-regulatory element analysis, these MtDof genes are regulated by different cis-acting motifs, which are important for the functional divergence of the MtDof genes in different processes. Thus, using genome-wide identification, evolution, and expression pattern analysis of the Dof genes in M. truncatula, our study provides valuable information for understanding the potential function of the Dof genes in regulating the growth and development of M. truncatula.
Assuntos
Proteínas de Arabidopsis/genética , Cromossomos de Plantas/química , Proteínas de Ligação a DNA/genética , Regulação da Expressão Gênica de Plantas , Genoma de Planta , Medicago truncatula/genética , Fatores de Transcrição/genética , Arabidopsis/genética , Evolução Biológica , Mapeamento Cromossômico , Sequência Conservada , Duplicação Gênica , Loci Gênicos , Sequenciamento de Nucleotídeos em Larga Escala , Medicago truncatula/classificação , Dados de Sequência Molecular , Família Multigênica , Motivos de Nucleotídeos , Oryza/genética , Filogenia , Isoformas de Proteínas/genética , Estrutura Terciária de ProteínaRESUMO
GRAS proteins play vital roles in plant growth and development. Physic nut (Jatropha curcas L.) was found to have a total of 48 GRAS family members (JcGRAS), 15 more than those found in Arabidopsis. The JcGRAS genes were divided into 12 subfamilies or 15 ancient monophyletic lineages based on the phylogenetic analysis of GRAS proteins from both flowering and lower plants. The functions of GRAS genes in 9 subfamilies have been reported previously for several plants, while the genes in the remaining 3 subfamilies were of unknown function; we named the latter families U1 to U3. No member of U3 subfamily is present in Arabidopsis and Poaceae species according to public genome sequence data. In comparison with the number of GRAS genes in Arabidopsis, more were detected in physic nut, resulting from the retention of many ancient GRAS subfamilies and the formation of tandem repeats during evolution. No evidence of recent duplication among JcGRAS genes was observed in physic nut. Based on digital gene expression data, 21 of the 48 genes exhibited differential expression in four tissues analyzed. Two members of subfamily U3 were expressed only in buds and flowers, implying that they may play specific roles. Our results provide valuable resources for future studies on the functions of GRAS proteins in physic nut.
Assuntos
Regulação da Expressão Gênica de Plantas , Genoma de Planta , Jatropha/genética , Filogenia , Proteínas de Plantas/genética , Fatores de Transcrição/genética , Arabidopsis/classificação , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Evolução Biológica , Mapeamento Cromossômico , Cromossomos de Plantas/química , Flores/genética , Flores/crescimento & desenvolvimento , Perfilação da Expressão Gênica , Jatropha/classificação , Jatropha/crescimento & desenvolvimento , Zíper de Leucina/genética , Anotação de Sequência Molecular , Família Multigênica , Estresse FisiológicoRESUMO
Bodao, a japonica landrace from the Taihu Lake region of China, is highly resistant to most Chinese isolates of Magnaporthe oryzea, a form of rice blast. To effectively dissect the influence of genetics on this blast resistance, a population of 155 recombinant inbred lines (F2:8) derived from a cross of Bodao x Suyunuo was inoculated with 12 blast isolates. Using a quantitative trait locus (QTL) mapping approach, 13 QTL on chromosomes 1, 2, 9, 11, and 12 were detected from Bodao. Five QTL, including qtl11-1-1, qtl11-3-7, qtl11-4-9, qtl12-1-1, and qtl12-2-3, have not been previously reported. The qtl11-3-7 and qtl11-4-9 may be the two main effective QTL and resistant to 7 and 9 isolates, respectively. The results of the present study will be valuable for the fine mapping and cloning of these two new resistance genes.
Assuntos
Cromossomos de Plantas/imunologia , Oryza/genética , Doenças das Plantas/imunologia , Imunidade Vegetal/genética , Locos de Características Quantitativas/imunologia , China , Mapeamento Cromossômico , Cromossomos de Plantas/química , Cruzamentos Genéticos , Magnaporthe/imunologia , Oryza/imunologia , Oryza/microbiologia , Doenças das Plantas/genética , Doenças das Plantas/microbiologiaRESUMO
We screened and assessed published cotton simple sequence repeat (SSR) primers to establish a set of core SSR markers suitable for cotton major cultivars in China and analyzed genetic diversity based on the core marker set. Using a stepwise screening strategy, 12 leading cultivars for preliminary screening and 96 cultivars for rescreening were evaluated. A total of 184 polymorphic SSR markers were initially screened from 3299 candidates, and a core set of 52 SSR markers with wide genome coverage (2 markers per chromosome) was obtained. Among 96 major cultivars, 273 amplification genotypes were generated using the core marker set. Polymorphism information content values ranged from 0.28-0.83, with an average value of 0.56. The core SSR marker set detected on denaturing polyacrylamide gel electrophoresis indicated that the band genotype was either a single or double band on conventional cultivars, while most were double bands (65.4%). Among 56 hybrids, the average heterozygosis rate was 35.8%, ranging from 7.1-55.4%. Eighteen of 96 cultivars had distinct band genotypes. The genetic diversity analyzed using the of NTSYS-pc V2.10 software indicated that the Yangtze River valley cotton region had the highest polymorphic level, followed by Xinjiang and then the Yellow River valley. The genetic basis of conventional cultivars was narrower than that of hybrids. The core marker set can be used for fingerprint construction, variety identification, and purity tests of major cotton cultivars in China.
Assuntos
Quimera/genética , Gossypium/genética , Repetições de Microssatélites , Polimorfismo Genético , Alelos , Cruzamento , Cromossomos de Plantas/química , Genótipo , Técnicas de Genotipagem , Gossypium/classificação , Heterozigoto , FilogeniaRESUMO
Leaf rolling occurs in some cereal genotypes in response to drought. We identified and made a phenotypic, cytological and physiological analysis of a leaf-rolling genotype (CMH83) of hexaploid triticale (X Triticosecale Wittmack) that exhibited reduced plant height, rolled and narrow leaves. Gliadin electrophoresis of seed protein showed that CMH83 was genetically stable. Sequential Giemsa-C-banding and genomic in situ hybridization showed that CMH83 contains 12 rye chromosomes; two pairs of these chromosomes have reduced telomeric heterochromatin bands. Tests of relative water content and water loss rate of leaves of CMH83 compared with those of wheat cultivars indicated that rapid water loss after drought stress in CMH83 is associated with the leaf rolling phenotypes. Leaf rolling in CMH83 was a dominant trait in our inheritance studies. Triticale line CMH83 could be used to study drought resistance mechanisms in triticale.
Assuntos
Cromossomos de Plantas/genética , Gliadina/genética , Folhas de Planta/genética , Secale/genética , Sementes/genética , Cromossomos de Plantas/química , Secas , Eletroforese em Gel de Poliacrilamida , Instabilidade Genômica , Genótipo , Gliadina/metabolismo , Heterocromatina/genética , Hibridização In Situ , Fenótipo , Ploidias , Telômero/genética , Triticum/genética , ÁguaRESUMO
The centromeric region of Costus spiralis is characteristically composed of a small heterochromatic DAPI(+) band flanked by a discrete decondensed region. High concentrations of serine 10 of histone H3 (H3S10ph) around the DAPI(+) band in pachytene chromosomes and the location of this heterochromatin at the chromosome region directed towards the poles during metaphase-anaphase I confirm its integration into the centromeric region. Antibodies against both typical components of euchromatin histones (histone H4 acetylated at lysine 5 (H4K5ac) and histone H3 dimethylated at lysine 4 (H3K4me2)) and heterochromatin (dimethylated lysine 9 of H3 (H3K9me2) and anti-5-methylcytosine (5-mC)) were used to characterize the centromeric chromatin of this species during meiosis. In pachytene chromosomes, the decondensed terminal euchromatin of the chromosome arms were seen to be richer in H4K5ac and H3K4me2 histones, while the more condensed proximal region was relatively stronger labeled with anti-H3K9me2 and anti-5-methylcytosine (5-mC). The centromeric region itself, including the DAPI(+) band, was poor in all of these chromatin modifications, but it was highly enriched in H4K5ac at pachytene. Before and after this stage, the centromeric region was poorly labeled with anti-H4K5ac. Hypomethylation and hyperacetylation of any kind of heterochromatin has rarely been reported, and it may be related to the dominant role of the centromere domain over the heterochromatin repeats.
Assuntos
Centrômero/genética , Cromossomos de Plantas/genética , Costus/genética , Heterocromatina/genética , 5-Metilcitosina/metabolismo , Acetilação , Cromatina/química , Cromatina/genética , Cromatina/metabolismo , Cromossomos de Plantas/química , Cromossomos de Plantas/metabolismo , Costus/química , Costus/metabolismo , Eucromatina/química , Eucromatina/genética , Eucromatina/metabolismo , Corantes Fluorescentes/química , Heterocromatina/química , Heterocromatina/metabolismo , Histonas/metabolismo , Imuno-Histoquímica , Indóis/química , Lisina/metabolismo , Metilação , Estágio Paquíteno/genética , Serina/metabolismoRESUMO
Secondary constrictions or 45S rDNA sites are commonly reported to be located mainly in the terminal regions of the chromosomes. This distribution has been assumed to be related to the existence of a "chromosome field" lying between the centromere and the telomere, an area in which certain cytogenetic events may predominantly occur. If this hypothesis is true this distribution should not be observed in holokinetic chromosomes, as they do not have a localized centromere. In order to evaluate this hypothesis, a comparative study was made of the distributions of 5S and 45S rDNA sites using fluorescence in situ hybridization in representatives of the genera Eleocharis, Diplacrum, Fimbristylis, Kyllinga and Rhynchospora, all of which belong to the family Cyperaceae. The numbers of sites per diploid chromosome complement varied from 2 to â¼10 for 5S rDNA, and from 2 to â¼45 for 45S rDNA. All of the 11 species analyzed had terminally located 45S rDNA sites on the chromosomes whereas the 5S rDNA sites also generally had terminal distributions, except for the Rhynchospora species, where their position was almost always interstitial. These results, together with other previously published data, suggest that the variation in the number and position of the rDNA sites in species with holokinetic chromosomes is non-random and similar to that reported for species with monocentric chromosomes. Therefore, the predominant terminal position of the 45S rDNA sites does not appear to be influenced by the centromere-telomere polarization as suggested by the "chromosome field" hypothesis. Additionally, the hybridization of 5S and 45S rDNA sites provides interesting markers to distinguish several chromosomes on the rather symmetrical karyotypes of Cyperaceae.
Assuntos
Cromossomos de Plantas/química , Plantas/química , RNA Ribossômico 5S/análise , RNA Ribossômico/análise , Centrômero/genética , Cyperaceae/genética , Hibridização in Situ Fluorescente , Cinética , Região Organizadora do Nucléolo , Telômero/genéticaRESUMO
BACKGROUND AND AIMS: Selaginella is the largest genus of heterosporous pteridophytes, but karyologically the genus is known only by the occurrence of a dysploid series of n=7-12, and a low frequency of polyploids. Aiming to contribute to a better understanding of the structural chromosomal variability of this genus, different staining methods were applied in species with different chromosome numbers. METHODS: The chromosome complements of seven species of Selaginella were analysed and, in four of them, the distribution of 45S rDNA sites was determined by fluorescent in situ hybridization. Additionally, CMA/DA/DAPI and silver nitrate staining were performed to investigate the correlation between the 45S rDNA sites, the heterochromatic bands and the number of active rDNA sites. KEY RESULTS: The chromosome numbers observed were 2n=18, 20 and 24. The species with 2n=20 exhibited chromosome complement sizes smaller and less variable than those with 2n=18. The only species with 2n=24, S. convoluta, had relatively large and asymmetrical chromosomes. The interphase nuclei in all species were of the chromocentric type. CMA/DA/DAPI staining showed only a weak chromosomal differentiation of heterochromatic bands. In S. willdenowii and S. convoluta eight and six CMA+ bands were observed, respectively, but no DAPI+ bands. The CMA+ bands corresponded in number, size and location to the rDNA sites. In general, the number of rDNA sites correlated with the maximum number of nucleoli per nucleus. Ten rDNA sites were found in S. plana (2n=20), eight in S. willdenowii (2n=18), six in S. convoluta (2n=24) and two in S. producta (2n=20). CONCLUSIONS: The remarkable variation in chromosome size and number and rDNA sites shows that dramatic karyological changes have occurred during the evolution of the genus at the diploid level. These data further suggest that the two putative basic numbers of the genus, x=9 and x=10, may have arisen two or more times independently.