RESUMO
BACKGROUND: Evolution of the Brassica species has been recursively affected by polyploidy events, and comparison to their relative, Arabidopsis thaliana, provides means to explore their genomic complexity. RESULTS: A genome-wide physical map of a rapid-cycling strain of B. oleracea was constructed by integrating high-information-content fingerprinting (HICF) of Bacterial Artificial Chromosome (BAC) clones with hybridization to sequence-tagged probes. Using 2907 contigs of two or more BACs, we performed several lines of comparative genomic analysis. Interspecific DNA synteny is much better preserved in euchromatin than heterochromatin, showing the qualitative difference in evolution of these respective genomic domains. About 67% of contigs can be aligned to the Arabidopsis genome, with 96.5% corresponding to euchromatic regions, and 3.5% (shown to contain repetitive sequences) to pericentromeric regions. Overgo probe hybridization data showed that contigs aligned to Arabidopsis euchromatin contain ~80% of low-copy-number genes, while genes with high copy number are much more frequently associated with pericentromeric regions. We identified 39 interchromosomal breakpoints during the diversification of B. oleracea and Arabidopsis thaliana, a relatively high level of genomic change since their divergence. Comparison of the B. oleracea physical map with Arabidopsis and other available eudicot genomes showed appreciable 'shadowing' produced by more ancient polyploidies, resulting in a web of relatedness among contigs which increased genomic complexity. CONCLUSIONS: A high-resolution genetically-anchored physical map sheds light on Brassica genome organization and advances positional cloning of specific genes, and may help to validate genome sequence assembly and alignment to chromosomes.All the physical mapping data is freely shared at a WebFPC site (http://lulu.pgml.uga.edu/fpc/WebAGCoL/brassica/WebFPC/; Temporarily password-protected: account: pgml; password: 123qwe123.
Assuntos
Brassica/genética , Mapeamento de Sequências Contíguas , Evolução Molecular , Genoma de Planta , Arabidopsis/genética , Cromossomos Artificiais Bacterianos , Hibridização Genômica Comparativa , DNA de Plantas/genética , Eucromatina/genética , Biblioteca Genômica , Heterocromatina/genética , Análise de Sequência de DNARESUMO
Publicly available genomic tools help researchers integrate information and make new discoveries. In this paper, we describe the development of immortal mapping populations of rapid cycling, self-compatible lines, molecular markers, and linkage maps for Brassica rapa and B. oleracea and make the data and germplasm available to the Brassica research community. The B. rapa population consists of 160 recombinant inbred (RI) lines derived from the cross of highly inbred lines of rapid cycling and yellow sarson B. rapa. The B. oleracea population consists of 155 double haploid (DH) lines derived from an F1 cross between two DH lines, rapid cycling and broccoli. A total of 120 RFLP probes, 146 SSR markers, and one phenotypic trait (flower color) were used to construct genetic linkage maps for both species. The B. rapa map consists of 224 molecular markers distributed along 10 linkage groups (A1-A10) with a total distance of 1125.3 cM and a marker density of 5.7 cM/marker. The B. oleracea genetic map consists of 279 molecular markers and one phenotypic marker distributed along nine linkage groups (C1-C9) with a total distance of 891.4 cM and a marker density of 3.2 cM/marker. A syntenic analysis with Arabidopsis thaliana identified collinear genomic blocks that are in agreement with previous studies, reinforcing the idea of conserved chromosomal regions across the Brassicaceae.
Assuntos
Brassica rapa/genética , Brassica/genética , Mapeamento Cromossômico , Bases de Dados Genéticas , Ligação Genética , Genética Populacional , Genoma de Planta , Arabidopsis/genética , Cromossomos de Plantas , Produtos Agrícolas/genética , Cruzamentos Genéticos , Genes de Plantas , Marcadores GenéticosRESUMO
Polyploidy has long been recognized as a prominent force shaping the evolution of eukaryotes, especially flowering plants. New phenotypes often arise with polyploid formation and can contribute to the success of polyploids in nature or their selection for use in agriculture. Although the causes of novel variation in polyploids are not well understood, they could involve changes in gene expression through increased variation in dosage-regulated gene expression, altered regulatory interactions, and rapid genetic and epigenetic changes. New research approaches are being used to study these mechanisms and the results should provide a more complete understanding of polyploidy.
Assuntos
Regulação da Expressão Gênica , Plantas/genética , Poliploidia , Evolução Biológica , Dosagem de Genes , Genes de Plantas , Variação Genética , Genoma de Planta , Modelos Genéticos , Seleção GenéticaRESUMO
Polyploidy has occurred throughout the evolutionary history of all eukaryotes and is extremely common in plants. Reunification of the evolutionarily divergent genomes in allopolyploids creates regulatory incompatibilities that must be reconciled. Here we report genomewide gene expression analysis of Arabidopsis synthetic allotetraploids, using spotted 70-mer oligo-gene microarrays. We detected >15% transcriptome divergence between the progenitors, and 2105 and 1818 genes were highly expressed in Arabidopsis thaliana and A. arenosa, respectively. Approximately 5.2% (1362) and 5.6% (1469) genes displayed expression divergence from the midparent value (MPV) in two independently derived synthetic allotetraploids, suggesting nonadditive gene regulation following interspecific hybridization. Remarkably, the majority of nonadditively expressed genes in the allotetraploids also display expression changes between the parents, indicating that transcriptome divergence is reconciled during allopolyploid formation. Moreover, >65% of the nonadditively expressed genes in the allotetraploids are repressed, and >94% of the repressed genes in the allotetraploids match the genes that are expressed at higher levels in A. thaliana than in A. arenosa, consistent with the silencing of A. thaliana rRNA genes subjected to nucleolar dominance and with overall suppression of the A. thaliana phenotype in the synthetic allotetraploids and natural A. suecica. The nonadditive gene regulation is involved in various biological pathways, and the changes in gene expression are developmentally regulated. In contrast to the small effects of genome doubling on gene regulation in autotetraploids, the combination of two divergent genomes in allotetraploids by interspecific hybridization induces genomewide nonadditive gene regulation, providing a molecular basis for de novo variation and allopolyploid evolution.
Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Regulação da Expressão Gênica de Plantas , Genoma de Planta , Poliploidia , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Evolução Biológica , Hibridização Genética , Análise de Sequência com Séries de Oligonucleotídeos , Polimorfismo Conformacional de Fita Simples , RNA de Plantas/genética , RNA de Plantas/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
Genetic maps of Brassica napus were constructed from four segregating populations of doubled haploid lines. Each mapping population had the same male parent and used the same set of RFLP probes, facilitating the construction of a consensus map. Chromosomal rearrangements were identified in each population by molecular marker analysis and were classified as de novo homologous nonreciprocal transpositions (HNRTs), preexisting HNRTs, and homologous reciprocal transpositions (HRTs). Ninety-nine de novo HNRTs were identified by the presence of a few lines having duplication of a chromosomal region and loss of the corresponding homologous region. These de novo HNRTs were more prevalent in one population that had a resynthesized B. napus as a parent. Preexisting HNRTs were identified by fragment duplication or fragment loss in many DH lines due to the segregation of HNRTs preexisting in one of the parents. Nine preexisting HNRTs were identified in the three populations involving natural B. napus parents, which likely originated from previous homologous exchanges. The male parent had a previously described HRT between N7 and N16, which segregated in each population. These data suggest that chromosomal rearrangements caused by homologous recombination are widespread in B. napus. The effects of these rearrangements on allelic and phenotypic diversity are discussed.
Assuntos
Brassica napus/genética , Mapeamento Cromossômico , Cromossomos de Plantas , Recombinação Genética , Alelos , Cromátides/genética , Cruzamentos Genéticos , Marcadores Genéticos , Haploidia , Modelos Genéticos , Polimorfismo de Fragmento de RestriçãoRESUMO
Over 1000 genetically linked RFLP loci in Brassica napus were mapped to homologous positions in the Arabidopsis genome on the basis of sequence similarity. Blocks of genetically linked loci in B. napus frequently corresponded to physically linked markers in Arabidopsis. This comparative analysis allowed the identification of a minimum of 21 conserved genomic units within the Arabidopsis genome, which can be duplicated and rearranged to generate the present-day B. napus genome. The conserved regions extended over lengths as great as 50 cM in the B. napus genetic map, equivalent to approximately 9 Mb of contiguous sequence in the Arabidopsis genome. There was also evidence for conservation of chromosome landmarks, particularly centromeric regions, between the two species. The observed segmental structure of the Brassica genome strongly suggests that the extant Brassica diploid species evolved from a hexaploid ancestor. The comparative map assists in exploiting the Arabidopsis genomic sequence for marker and candidate gene identification within the larger, intractable genomes of the Brassica polyploids.
Assuntos
Arabidopsis/genética , Brassica napus/genética , Mapeamento Cromossômico , Evolução Molecular , Genoma de Planta/genética , Sequência de Bases , Sequência Conservada/genética , DNA Complementar/genética , Dados de Sequência Molecular , Ploidias , Polimorfismo de Fragmento de Restrição , Análise de Sequência de DNA , Especificidade da EspécieRESUMO
Functional genetic redundancy is widespread in plants and could have an important impact on phenotypic diversity if the multiple gene copies act in an additive or dosage-dependent manner. We have cloned four Brassica rapa homologs (BrFLC) of the MADS-box flowering-time regulator FLC, located at the top of chromosome 5 of Arabidopsis thaliana. Relative rate tests revealed no evidence for differential rates of evolution and the ratios of nonsynonymous-to-synonymous substitutions suggest BrFLC loci are not under strong purifying selection. BrFLC1, BrFLC2, and BrFLC3 map to genomic regions that are collinear with the top of At5, consistent with a polyploid origin. BrFLC5 maps near a junction of two collinear regions to Arabidopsis, one of which includes an FLC-like gene (AGL31). However, all BrFLC sequences are more closely related to FLC than to AGL31. BrFLC1, BrFLC2, and BrFLC5 cosegregate with flowering-time loci evaluated in populations derived by backcrossing late-flowering alleles from a biennial parent into an annual parent. Two loci segregating in a single backcross population affected flowering in a completely additive manner. Thus, replicated BrFLC genes appear to have a similar function and interact in an additive manner to modulate flowering time.
Assuntos
Brassica rapa/genética , Flores/genética , Duplicação Gênica , Proteínas de Domínio MADS/genética , Sequência de Bases , Brassica rapa/crescimento & desenvolvimento , Mapeamento Cromossômico , Clonagem Molecular , Flores/crescimento & desenvolvimento , Proteínas de Domínio MADS/metabolismo , Dados de Sequência Molecular , Filogenia , Locos de Características Quantitativas , Análise de Sequência de DNARESUMO
A reciprocal chromosomal transposition was identified in several annual oilseed Brassica napus genotypes used as parents in crosses to biennial genotypes for genetic mapping studies. The transposition involved an exchange of interstitial homeologous regions on linkage groups N7 and N16, and its detection was made possible by the use of segregating populations of doubled haploid lines and codominant RFLP markers. RFLP probes detected pairs of homeologous loci on N7 and N16 for which the annual and biennial parents had identical alleles in regions expected to be homeologous. The existence of an interstitial reciprocal transposition was confirmed by cytological analysis of synaptonemal complexes of annual x biennial F1 hybrids. Although it included approximately one-third of the physical length of the N7 and N16 chromosomes, few recombination events within the region were recovered in the progenies of the hybrids. Significantly higher seed yields were associated with the parental configurations of the rearrangement in segregating progenies. These progenies contained complete complements of homeologous chromosomes from the diploid progenitors of B. napus, and thus their higher seed yields provide evidence for the selective advantage of allopolyploidy through the fixation of intergenomic heterozygosity.
Assuntos
Brassica/genética , Cromossomos de Plantas , Polimorfismo de Fragmento de RestriçãoRESUMO
Synthetic oligonucleotides (oligos) represent an attractive alternative to cDNA amplicons for spotted microarray analysis in a number of model organisms, including Arabidopsis, C. elegans, Drosophila, human, mouse and yeast. However, little is known about the relative effectiveness of 60-70-mer oligos and cDNAs for detecting gene expression changes. Using 192 pairs of Arabidopsis thaliana cDNAs and corresponding 70-mer oligos, we performed three sets of dye-swap experiments and used analysis of variance (anova) to compare sources of variation and sensitivities for detecting gene expression changes in A. thaliana, A. arenosa and Brassica oleracea. Our major findings were: (1) variation among different RNA preparations from the same tissue was small, but large variation among dye-labellings and slides indicates the need to replicate these factors; (2) sources of variation were similar for experiments with all three species, suggesting these feature types are effective for analysing gene expression in related species; (3) oligo and cDNA features had similar sensitivities for detecting expression changes and they identified a common subset of significant genes, but results from quantitative RT-PCR did not support the use of one over the other. These findings indicate that spotted oligos are at least as effective as cDNAs for microarray analyses of gene expression. We are using oligos designed from approximately 26,000 annotated genes of A. thaliana to study gene expression changes in Arabidopsis and Brassica polyploids.
RESUMO
Increased production of rapeseed in the north central and southeastern regions of the United States has been accompanied by an increase in the incidence of blackleg disease caused by Leptosphaeria maculans. In order to assess the genetic variability and relatedness of isolates from these regions to others from around the world, we analyzed 49 aggressive isolates representing three pathogenicity groups (PG2, 3, and 4) of L. maculans from North Dakota, Georgia, Ontario, Western Canada, the United Kingdom (UK), France, Germany, and Australia using pathogenicity data and amplified fragment length polymorphism (AFLP). Approximately 10% of the 400 amplified fragments were polymorphic, scored as discrete characters and analyzed by cluster analysis. The isolates from North Dakota, Western Canada, Georgia, and PHW1252 from the UK formed one tightly clustered group and were mostly of the same pathogenicity group; whereas isolates from Ontario, Australia, France, Germany, and the remaining isolates from the UK formed a second group, which exhibited greater variation and consisted of three pathogenicity groups. The similarity between North Dakota isolates collected in 1995-96 and Western Canadian isolates collected in the 1980s suggests that L. maculans was introduced into North Dakota from Western Canada, and that the populations have remained relatively unchanged over the past 10 years.
RESUMO
BACKGROUND: Studies in resynthesized Brassica napus allopolyploids indicate that homoeologous chromosome exchanges in advanced generations (S(5ratio6)) alter gene expression through the loss and doubling of homoeologous genes within the rearrangements. Rearrangements may also indirectly affect global gene expression if homoeologous copies of gene regulators within rearrangements have differential affects on the transcription of genes in networks. METHODOLOGY/PRINCIPAL FINDINGS: We utilized Arabidopsis 70mer oligonucleotide microarrays for exploring gene expression in three resynthesized B. napus lineages at the S(0ratio1) and S(5ratio6) generations as well as their diploid progenitors B. rapa and B. oleracea. Differential gene expression between the progenitors and additive (midparent) expression in the allopolyploids were tested. The S(5ratio6) lines differed in the number of genetic rearrangements, allowing us to test if the number of genes displaying nonadditive expression was related to the number of rearrangements. Estimates using per-gene and common variance ANOVA models indicated that 6-15% of 26,107 genes were differentially expressed between the progenitors. Individual allopolyploids showed nonadditive expression for 1.6-32% of all genes. Less than 0.3% of genes displayed nonadditive expression in all S(0ratio1) lines and 0.1-0.2% were nonadditive among all S(5ratio6) lines. Differentially expressed genes in the polyploids were over-represented by genes differential between the progenitors. The total number of differentially expressed genes was correlated with the number of genetic changes in S(5ratio6) lines under the common variance model; however, there was no relationship using a per-gene variance model, and many genes showed nonadditive expression in S(0ratio1) lines. CONCLUSIONS/SIGNIFICANCE: Few genes reproducibly demonstrated nonadditive expression among lineages, suggesting few changes resulted from a general response to polyploidization. Furthermore, our microarray analysis did not provide strong evidence that homoeologous rearrangements were a determinant of genome-wide nonadditive gene expression. In light of the inherent limitations of the Arabidopsis microarray to measure gene expression in polyploid Brassicas, further studies are warranted.
Assuntos
Arabidopsis/genética , Brassica napus/genética , Regulação da Expressão Gênica de Plantas , Poliploidia , Perfilação da Expressão Gênica/métodos , Rearranjo Gênico , Redes Reguladoras de Genes , Análise de Sequência com Séries de OligonucleotídeosRESUMO
The traditional development of simple sequence repeat (SSR) or microsatellite markers by probe hybridization can be time-consuming and requires the use of specialized laboratory equipment. In this study, probe hybridization was circumvented by using sequence information on 3,500 genomic clones mainly from Brassica oleracea to identify di, tri, tetra and penta-nucleotide repeats. A total of 587 primer pairs flanking SSR were developed using this approach. From these, 420 SSR markers amplified DNA in two parental lines of B. rapa (26% were polymorphic) and 523 in two parental lines of B. oleracea (32% were polymorphic). A diverse array of motif types was identified, characterized and compared with traditional SSR detection methods. The most abundant motifs found were di- (38%) and trinucleotides (33%) followed by penta- (16%) and tetranucleotide (13%) motifs. The type of motif class, motif length and repeat were not indicative of polymorphisms. The frequency of B. oleracea SSRs in genomic shotgun sequence was estimated to be 1 every 4 Kb. In general, the average motif length and repeat numbers were shorter than those obtained previously by probe hybridization, and they contained a more balanced representation of SSR motif types in the genome by identifying those that do not hybridize well to DNA probes. Brassica genomic DNA sequence information is a promising resource for developing a large number of SSR molecular markers in Brassica species.
Assuntos
Brassica/genética , DNA de Plantas/genética , Repetições Minissatélites , Sequência de Bases , Brassica/classificação , Brassica rapa/genética , Marcadores Genéticos , Técnicas Genéticas , Genoma de Planta , Genótipo , Polimorfismo Genético , Especificidade da EspécieRESUMO
The phylogenetic history of Medicago was examined for 60 accessions from 56 species using two nuclear genes (CNGC5 and beta-cop) and one mitochondrial region (rpS14-cob). The results of several analyses revealed that extensive robustly supported incongruence exists among the nuclear genes, the cause of which we seek to explain. After rejecting several processes, hybridization and lineage sorting of ancestral polymorphisms remained as the most likely factors promoting incongruence. Using coalescence simulations, we rejected lineage sorting alone as an explanation of the differences among gene trees. The results indicate that hybridization has been common and ongoing among lineages since the origin of Medicago. Coalescence provides a good framework to test the causes of incongruence commonly seen among gene trees but requires knowledge of effective population sizes and generation times. We estimated the effective population size at 240,000 individuals and assumed a generation time of 1 year in Medicago (many are annual plants). A sensitivity analysis showed that our conclusions remain unchanged using a larger effective population size and/or longer generation time.
Assuntos
Medicago/classificação , Filogenia , Teorema de Bayes , Proteína Coatomer/química , Simulação por Computador , Canais de Cátion Regulados por Nucleotídeos Cíclicos/química , DNA Mitocondrial/química , DNA de Plantas/química , Diploide , Ligação Genética , Hibridização Genética , Medicago/genética , Medicago/ultraestrutura , Modelos Genéticos , Proteínas de Plantas/química , Poliploidia , Análise de Sequência de DNARESUMO
Many previous studies have provided evidence for genome changes in polyploids, but there are little data on the overall population dynamics of genome change and whether it causes phenotypic variability. We analyzed genetic, epigenetic, gene expression, and phenotypic changes in approximately 50 resynthesized Brassica napus lines independently derived by hybridizing double haploids of Brassica oleracea and Brassica rapa. A previous analysis of the first generation (S0) found that genetic changes were rare, and cytosine methylation changes were frequent. Our analysis of a later generation found that most S0 methylation changes remained fixed in their S5 progeny, although there were some reversions and new methylation changes. Genetic changes were much more frequent in the S5 generation, occurring in every line with lines normally distributed for number of changes. Genetic changes were detected on 36 of the 38 chromosomes of the S5 allopolyploids and were not random across the genome. DNA fragment losses within lines often occurred at linked marker loci, and most fragment losses co-occurred with intensification of signal from homoeologous markers, indicating that the changes were due to homoeologous nonreciprocal transpositions (HNRTs). HNRTs between chromosomes A1 and C1 initiated in early generations, occurred in successive generations, and segregated, consistent with a recombination mechanism. HNRTs and deletions were correlated with qualitative changes in the expression of specific homoeologous genes and anonymous cDNA amplified fragment length polymorphisms and with phenotypic variation among S5 polyploids. Our data indicate that exchanges among homoeologous chromosomes are a major mechanism creating novel allele combinations and phenotypic variation in newly formed B. napus polyploids.
Assuntos
Brassica napus/genética , Regulação da Expressão Gênica de Plantas , Genoma de Planta/genética , Análise do Polimorfismo de Comprimento de Fragmentos Amplificados , Segregação de Cromossomos , Cromossomos de Plantas/metabolismo , Metilação de DNA , Elementos de DNA Transponíveis , DNA Complementar/metabolismo , DNA de Plantas/metabolismo , Ligação Genética , Marcadores Genéticos , Fenótipo , Filogenia , Polimorfismo Conformacional de Fita Simples , Poliploidia , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Recombinação Genética/genéticaRESUMO
Sclerotinia sclerotiorum is a necrotrophic plant pathogen which causes serious disease in agronomically important crop species. The molecular basis of plant defense to this pathogen is poorly understood. We investigated gene expression changes associated with S. sclerotiorum infection in a partially resistant and a susceptible genotype of oilseed Brassica napus using a whole genome microarray from Arabidopsis. A total of 686 and 1,547 genes were found to be differentially expressed after infection in the resistant and susceptible genotypes, respectively. The number of differentially expressed genes increased over infection time with the majority being up-regulated in both genotypes. The putative functions of the differentially expressed genes included pathogenesis-related (PR) proteins, proteins involved in the oxidative burst, protein kinase, molecule transporters, cell maintenance and development, abiotic stress, as well as proteins with unknown functions. The gene regulation patterns indicated that a large part of the defense response exhibited as a temporal and quantitative difference between the two genotypes. Genes associated with jasmonic acid (JA) and ethylene signal transduction pathways were induced, but no salicylic acid (SA) responsive genes were identified. Candidate defense genes were identified by integration of the early response genes in the partially resistant line with previously mapped quantitative trait loci (QTL). Expression levels of these genes were verified by Northern blot analyses. These results indicate that genes encoding various proteins involved in diverse roles, particularly WRKY transcription factors and plant cell wall related proteins may play an important role in the defense response to S. sclerotiorum disease.
Assuntos
Ascomicetos/crescimento & desenvolvimento , Brassica napus/genética , Brassica napus/microbiologia , Perfilação da Expressão Gênica/métodos , Arabidopsis/genética , Northern Blotting , Regulação da Expressão Gênica de Plantas , Genoma de Planta , Análise de Sequência com Séries de Oligonucleotídeos/métodos , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
Unadapted germplasm may contain alleles that could improve hybrid cultivars of spring oilseed Brassica napus. Quantitative trait loci (QTL) mapping was used to identify potentially useful alleles from two unadapted germplasm sources, a Chinese winter cultivar and a re-synthesized B. napus, that increase seed yield when introgressed into a B. napus spring hybrid combination. Two populations of 160 doubled haploid (DH) lines were created from crosses between the unadapted germplasm source and a genetically engineered male-fertility restorer line (P1804). A genetically engineered male-sterile tester line was used to create hybrids with each DH line (testcrosses). The two DH line populations were evaluated in two environments and the two testcross populations were evaluated in three or four environments for seed yield and other agronomic traits. Several genomic regions were found in the two testcross populations which contained QTL for seed yield. The map positions of QTL for days to flowering and resistance to a bacterial leaf blight disease coincided with QTL for seed yield and other agronomic traits, suggesting the occurrence of pleiotropic or linked effects. For two hybrid seed yield QTL, the favorable alleles increasing seed yield originated from the unadapted parents, and one of these QTL was detected in multiple environments and in both populations. In this QTL region, a chromosome rearrangement was identified in P1804, which may have affected seed yield.
Assuntos
Alelos , Brassica napus/genética , Locos de Características Quantitativas , Sementes/crescimento & desenvolvimento , Brassica napus/embriologia , Mapeamento Cromossômico , Cromossomos de Plantas , Ligação Genética , Variação Genética , Haploidia , Hibridização Genética , Imunidade Inata/genéticaRESUMO
The introgression of winter germplasm into spring canola (Brassica napus L.) represents a novel approach to improve seed yield of hybrid spring canola. In this study, quantitative trait loci (QTL) for seed yield and other traits were genetically mapped to determine the effects of genomic regions introgressed from winter germplasm into spring canola. Plant materials used comprised of two populations of doubled haploid (DH) lines having winter germplasm introgression from two related French winter cultivars and their testcrosses with a spring line used in commercial hybrids. These populations were evaluated for 2 years at two locations (Wisconsin, USA and Saskatchewan, Canada). Genetic linkage maps based on RFLP loci were constructed for each DH population. Six QTL were detected in the testcross populations for which the winter alleles increased seed yield. One of these QTL explained 11 and 19% of the phenotypic variation in the two Canadian environments. The winter allele for another QTL that increased seed yield was linked in coupling to a QTL allele for high glucosinolate content, suggesting that the transition of rapeseed into canola could have resulted in the loss of favorable seed yield alleles. Most QTL for which the introgressed allele decreased seed yield of hybrids mapped to genomic regions having homoeologous non-reciprocal transpositions. This suggests that allelic configurations created by these rearrangements might make an important contribution to genetic variation for complex traits in oilseed B. napus and could account for a portion of the heterotic effects in hybrids.
Assuntos
Brassica napus/genética , Locos de Características Quantitativas , Sementes/crescimento & desenvolvimento , Alelos , Brassica napus/anatomia & histologia , Brassica napus/embriologia , Quimera/anatomia & histologia , Quimera/embriologia , Quimera/genética , Mapeamento Cromossômico , Análise por Conglomerados , Flores/genética , Flores/crescimento & desenvolvimento , Rearranjo Gênico , Ligação Genética , Variação Genética , Genômica , Fenótipo , Doenças das Plantas/genética , Sementes/genéticaRESUMO
Sclerotinia stem rot, caused by fungus Sclerotinia sclerotiorum, is one of the most devastating diseases in rapeseed (Brassica napus L.). We report the identification of Quantitative trait loci (QTL) involved in the resistance to S. sclerotiorum in two segregating populations of DH lines: the HUA population, derived from a cross between a partially resistant Chinese winter line (Hua dbl2) and a susceptible European spring line (P1804); and the MS population, derived from a partially resistant French winter cultivar (Major) and a susceptible Canadian spring cultivar (Stellar). A petiole inoculation technique and two scoring methods, days to wilt (DW) and stem lesion length (SLL), were used for the resistance assessment. A total of eight genomic regions affecting resistance were detected in the HUA population, with four of these regions affecting both measures of resistance. Only one region, which affected both measurements, was detected in the MS population. Individual QTL explained 6-22% of the variance. At five of the QTL from both populations, alleles from the resistant parent contributed to the resistance. QTL on N2 from the HUA population had the highest LOD score and R (2) value and was detected for SLL in the first evaluation. The N12 resistance allele in Hua dbl2 was detected in a region containing a homeologous non-reciprocal transposition (HNRT) from the resistance-containing portion of N2. This result suggests that QTL in the N12.N2 HNRT enhanced the resistance of Hua dbl2 by increasing the dosage of resistance genes. The relationship of QTL from different genetic backgrounds and their associations with other agronomic traits are discussed.
Assuntos
Ascomicetos , Brassica napus/microbiologia , Imunidade Inata/genética , Doenças das Plantas/microbiologia , Locos de Características Quantitativas , Brassica napus/genética , Mapeamento Cromossômico , Cromossomos de Plantas , Cruzamentos Genéticos , Doenças das Plantas/genéticaRESUMO
Mutations in the biosynthesis or signaling pathways of gibberellin (GA) can cause dwarfing phenotypes in plants, and the use of such mutations in plant breeding was a major factor in the success of the Green Revolution. DELLA proteins are GA signaling repressors whose functions are conserved in different plant species. Recent studies show that GA promotes stem growth by causing degradation of DELLA proteins via the ubiquitin-proteasome pathway. The most widely utilized dwarfing alleles in wheat (Triticum aestivum; e.g. Rht-B1b and Rht-D1b) encode GA-resistant forms of a DELLA protein that function as dominant and constitutively active repressors of stem growth. All of the previously identified dominant DELLA repressors from several plant species contain N-terminal mutations. Here we report on a novel dwarf mutant from Brassica rapa (Brrga1-d) that is caused by substitution of a conserved amino acid in the C-terminal domain of a DELLA protein. Brrga1-d, like N-terminal DELLA mutants, retains its repressor function and accumulates to high levels, even in the presence of GA. However, unlike wild-type and N-terminal DELLA mutants, Brrga1-d does not interact with a protein component required for degradation, suggesting that the mutated amino acid causes dwarfism by preventing an interaction needed for its degradation. This novel mutation confers nondeleterious dwarf phenotypes when transferred to Arabidopsis (Arabidopsis thaliana) and oilseed rape (Brassica napus), indicating its potential usefulness in other crop species.
Assuntos
Brassica rapa/crescimento & desenvolvimento , Brassica rapa/genética , Giberelinas/metabolismo , Sequência de Aminoácidos , Arabidopsis/genética , Arabidopsis/fisiologia , Regulação da Expressão Gênica de Plantas/genética , Regulação da Expressão Gênica de Plantas/fisiologia , Dados de Sequência Molecular , Mutação , Fenótipo , Proteínas de Plantas/química , Proteínas de Plantas/genética , Saccharomyces cerevisiae , Homologia de Sequência de Aminoácidos , Transdução de Sinais , Técnicas do Sistema de Duplo-HíbridoRESUMO
Variation that arises in generations immediately following polyploidization may be important for the establishment, adaptation, and persistence of new polyploid species. We previously showed divergence for flowering time among lines from a resynthesized Brassica napus allopolyploid lineage derived from a cross of diploid B. rapa and B. oleracea. In this study, we more fully assess phenotypic differentiation of lines from the previously studied lineage and of lines derived from an additional resynthesized B. napus lineage. Nine polyploid lines and their diploid parents were grown under four growth conditions and measured for eight life-history traits. Polyploid lines within a lineage were expected to be genetically identical because they were derived from individual, chromosome-doubled amphihaploid plants. However, significant differences were found among lines within lineages for every phenotypic trait measured and in response to different growth conditions (genotype by environment interactions). When phenotypes of each polyploid line for each trait in each environment were compared with their diploid progenitors, approximately 30% were like one or the other parent, 50% were intermediate, and 20% were transgressive. Our results demonstrate extensive de novo variation in new polyploid lineages. Such changes could contribute to the evolutionary potential in naturally occurring polyploids.