Sex-Specific Crossover Distributions and Variations in Interference Level along Arabidopsis thaliana Chromosome 4

In many species, sex-related differences in crossover (CO) rates have been described at chromosomal and regional levels. In this study, we determined the CO distribution along the entire Arabidopsis thaliana Chromosome 4 (18 Mb) in male and female meiosis, using high density genetic maps built on large backcross populations (44 markers, >1,300 plants). We observed dramatic differences between male and female map lengths that were calculated as 88 cM and 52 cM, respectively. This difference is remarkably parallel to that between the total synaptonemal complex lengths measured in male and female meiocytes by immunolabeling of ZYP1 (a component of the synaptonemal complex). Moreover, CO landscapes were clearly different: in particular, at both ends of the map, male CO rates were higher (up to 4-fold the mean value), whereas female CO rates were equal or even below the chromosomal average. This unique material gave us the opportunity to perform a detailed analysis of CO interference on Chromosome 4 in male and female meiosis. The number of COs per chromosome and the distances between them clearly departs from randomness. Strikingly, the interference level (measured by coincidence) varied significantly along the chromosome in male meiosis and was correlated to the physical distance between COs. The significance of this finding on the relevance of current CO interference models is discussed

Energy supply of countryside based on geothermal deposit

Meiosis is a specialized eukaryotic cell division that generates haploid gametes required for sexual reproduction. During meiosis, homologous chromosomes pair and undergo reciprocal genetic exchange, termed crossover (CO). Meiotic CO frequency varies along the physical length of chromosomes and is determined by hierarchical mechanisms, including epigenetic organization, for example methylation of the DNA and histones. Here we investigate the role of DNA methylation in determining patterns of CO frequency along Arabidopsis thaliana chromosomes. In A. thaliana the pericentromeric regions are repetitive, densely DNA methylated, and suppressed for both RNA polymerase-II transcription and CO frequency. DNA hypomethylated methyltransferase1 (met1) mutants show transcriptional reactivation of repetitive sequences in the pericentromeres, which we demonstrate is coupled to extensive remodeling of CO frequency. We observe elevated centromere-proximal COs in met1, coincident with pericentromeric decreases and distal increases. Importantly, total numbers of CO events are similar between wild type and met1, suggesting a role for interference and homeostasis in CO remodeling. To understand recombination distributions at a finer scale we generated CO frequency maps close to the telomere of chromosome 3 in wild type and demonstrate an elevated recombination topology in met1. Using a pollen-typing strategy we have identified an intergenic nucleosome-free CO hotspot 3a, and we demonstrate that it undergoes increased recombination activity in met1. We hypothesize that modulation of 3a activity is caused by CO remodeling driven by elevated centromeric COs. These data demonstrate how regional epigenetic organization can pattern recombination frequency along eukaryotic chromosomes

Epigenetic Remodeling of Meiotic Crossover Frequency in Arabidopsis thaliana DNA Methyltransferase Mutants

Meiosis is a specialized eukaryotic cell division that generates haploid gametes required for sexual reproduction. During meiosis, homologous chromosomes pair and undergo reciprocal genetic exchange, termed crossover (CO). Meiotic CO frequency varies along the physical length of chromosomes and is determined by hierarchical mechanisms, including epigenetic organization, for example methylation of the DNA and histones. Here we investigate the role of DNA methylation in determining patterns of CO frequency along Arabidopsis thaliana chromosomes. In A. thaliana the pericentromeric regions are repetitive, densely DNA methylated, and suppressed for both RNA polymerase-II transcription and CO frequency. DNA hypomethylated methyltransferase1 (met1) mutants show transcriptional reactivation of repetitive sequences in the pericentromeres, which we demonstrate is coupled to extensive remodeling of CO frequency. We observe elevated centromere-proximal COs in met1, coincident with pericentromeric decreases and distal increases. Importantly, total numbers of CO events are similar between wild type and met1, suggesting a role for interference and homeostasis in CO remodeling. To understand recombination distributions at a finer scale we generated CO frequency maps close to the telomere of chromosome 3 in wild type and demonstrate an elevated recombination topology in met1. Using a pollen-typing strategy we have identified an intergenic nucleosome-free CO hotspot 3a, and we demonstrate that it undergoes increased recombination activity in met1. We hypothesize that modulation of 3a activity is caused by CO remodeling driven by elevated centromeric COs. These data demonstrate how regional epigenetic organization can pattern recombination frequency along eukaryotic chromosomes

Genome-Wide Crossover Distribution in Arabidopsis thaliana Meiosis Reveals Sex-Specific Patterns along Chromosomes

In most species, crossovers (COs) are essential for the accurate segregation of homologous chromosomes at the first meiotic division. Their number and location are tightly regulated. Here, we report a detailed, genome-wide characterization of the rate and localization of COs in Arabidopsis thaliana, in male and female meiosis. We observed dramatic differences between male and female meiosis which included: (i) genetic map length; 575 cM versus 332 cM respectively; (ii) CO distribution patterns: male CO rates were very high at both ends of each chromosome, whereas female CO rates were very low; (iii) correlations between CO rates and various chromosome features: female CO rates correlated strongly and negatively with GC content and gene density but positively with transposable elements (TEs) density, whereas male CO rates correlated positively with the CpG ratio. However, except for CpG, the correlations could be explained by the unequal repartition of these sequences along the Arabidopsis chromosome. For both male and female meiosis, the number of COs per chromosome correlates with chromosome size expressed either in base pairs or as synaptonemal complex length. Finally, we show that interference modulates the CO distribution both in male and female meiosis

Genome sequence comparison of Col and Ler lines reveals the dynamic nature of Arabidopsis chromosomes

Large differences in plant genome sizes are mainly due to numerous events of insertions or deletions (indels). The balance between these events determines the evolutionary direction of genome changes. To address the question of what phenomena trigger these alterations, we compared the genomic sequences of two Arabidopsis thaliana lines, Columbia (Col) and Landsberg erecta (Ler). Based on the resulting alignments large indels (>100 bp) within these two genomes were analysed. There are ∼8500 large indels accounting for the differences between the two genomes. The genetic basis of their origin was distinguished as three main categories: unequal recombination (Urec)-derived, illegitimate recombination (Illrec)-derived and transposable elements (TE)-derived. A detailed study of their distribution and size variation along chromosomes, together with a correlation analyses, allowed us to demonstrate the impact of particular recombination-based mechanisms on the plant genome evolution. The results show that unequal recombination is not efficient in the removal of TEs within the pericentromeric regions. Moreover, we discovered an unexpectedly high influence of large indels on gene evolution pointing out significant differences between the various gene families. For the first time, we present convincing evidence that somatic events do play an important role in plant genome evolution

Etude de promoteurs spécifiques de la microsporogenèse chez le colza

il s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : DISSERTATIONEtude de promoteurs spécifiques de la microsporogenèse chez le colz

Etude de la distribution des événements de recombinaison méiotique chez arabidopsis thaliana

ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

The road to crossovers: plants have their say

Crossovers involve the reciprocal exchange of large fragments of genetic material between homologous chromosomes during meiosis. In this way, crossovers are the basis of genetics. Remarkably, the number and distribution of crossovers on chromosomes are closely controlled. Data from various model organisms (notably Saccharomyces cerevisiae) show that the distribution of crossovers results from a series of tightly regulated events involving the formation and repair of double-strand breaks and interference. Recent advances in genetic and cytological tools, particularly for studying Arabidopsis thaliana, have enabled crossover control in plants to be studied in more detail. In this article, we discuss the contribution of plant studies to meiosis research, particularly to our understanding of crossover control and interference, and we evaluate models of interference

Variability in six pea gene sequences and mapping through PCR-based markers

Despite the rapid increase in sequence databases, gene sequences are still under-used in the plant breeding and genetic mapping area. This study was conducted to determine whether pea gene sequences contained enough polymorphism to be used as genetic markers. Molecular variability was examined at the DNA sequence level within different lines and wild ecotypes of Pisum sativum. The analysis was conducted for several introns, exons and 5'UTR sequences from six nuclear genes (GAPC, PHYA and IAA-related genes). Each region was specifically amplified and polymorphism was identified by electrophoretic mobility and by direct sequencing of PCR products. The observed polymorphism illustrates the possibility of developing molecular markers since all the analyzed loci have been successfully localised. Polymorphism was detected either as DNA conformational polymorphism following non-denaturing polyacrylamide gel electrophoresis or as CAPS (cleaved amplified polymorphism sequence). The noteworthy property of such genetic markers is their ability to establish bridges between different existing pea genetic maps. (© Inra/Elsevier, Paris.)Analyse de la variabilité des séquences de six gènes de pois et cartographie génétique par PCR. Malgré l'accroissement rapide des bases de données, les séquences des gènes sont encore sous-exploitées dans le domaine de l'amélioration des plantes et de la cartographie génétique. Cette étude a été menée pour déterminer si les séquences des gènes du pois renferment suffisamment de polymorphisme pour générer des marqueurs génétiques. La variabilité moléculaire a été examinée au niveau de la séquence de l'ADN entre différentes lignées et écotypes sauvages de Pisum sativum. Cette analyse a été effectuée pour plusieurs séquences introniques, exoniques et promotrices de six gènes nucléaires (GAPC, PHYA, et gènes apparentés aux gènes IAA). Chaque région a été amplifiée spécifiquement et le polymorphisme a été identifié par la mobilité électrophorétique et par séquençage direct des produits de PCR. Le polymorphisme observé illustre la possibilité de développer des marqueurs moléculaires puisque tous les loci analysés ont pu être cartographiés. Le polymorphisme est détecté soit comme un polymorphisme de conformation de l'ADN après une électrophorèse dans un gel d'acrylamide dans des conditions non dénaturantes, soit comme des CAPS (Cleaved Amplified Polymorphism Sequence). La propriété remarquable de tels marqueurs génétiques est leur capacité à établir des ponts entre les différentes cartes génétiques existantes chez le pois. (© Inra/Elsevier, Paris.

Study of an UBX gene sub-family that is preferentially expressed in pollen: functional genes or pseudogenes ?

Study of an UBX gene sub-family that is preferentially expressed in pollen: functional genes or pseudogenes ?. 7. Colloque national de la SFB