Speciation Success of Polyploid Plants Closely Relates to the Regulation of Meiotic Recombination

Polyploidization is a widespread phenomenon, especially in flowering plants that have all undergone at least one event of whole genome duplication during their evolutionary history. Consequently, a large range of plants, including many of the world’s crops, combines more than two sets of chromosomes originating from the same (autopolyploids) or related species (allopolyploids). Depending on the polyploid formation pathway, different patterns of recombination will be promoted, conditioning the level of heterozygosity. A polyploid population harboring a high level of heterozygosity will produce more genetically diverse progenies. Some of these individuals may show a better adaptability to different ecological niches, increasing their chance for successful establishment through natural selection. Another condition for young polyploids to survive corresponds to the formation of well-balanced gametes, assuring a sufficient level of fertility. In this review, we discuss the consequences of polyploid formation pathways, meiotic behavior and recombination regulation on the speciation success and maintenance of polyploid species

Natural variation identifies SNI1, the SMC5/6 component, as a modifier of meiotic crossover in Arabidopsis.

The frequency and distribution of meiotic crossovers are tightly controlled; however, variation in this process can be observed both within and between species. Using crosses of two natural Arabidopsis thaliana accessions, Col and Ler, we mapped a crossover modifier locus to semidominant polymorphisms in SUPPRESSOR OF NPR1-1 INDUCIBLE 1 (SNI1), which encodes a component of the SMC5/6 complex. The sni1 mutant exhibits a modified pattern of recombination across the genome with crossovers elevated in chromosome distal regions but reduced in pericentromeres. Mutations in SNI1 result in reduced crossover interference and can partially restore the fertility of a Class I crossover pathway mutant, which suggests that the protein affects noninterfering crossover repair. Therefore, we tested genetic interactions between SNI1 and both RECQ4 and FANCM DNA helicases, which showed that additional Class II crossovers observed in the sni1 mutant are FANCM independent. Furthermore, genetic analysis of other SMC5/6 mutants confirms the observations of crossover redistribution made for SNI1 The study reveals the importance of the SMC5/6 complex in ensuring the proper progress of meiotic recombination in plants

Impact of ploidy level and genome evolution on the control of the frequency and distribution of recombination events in Brassicas

La recombinaison méiotique via les Crossing-Overs (COs) est le principal mécanisme permettant le brassage de la diversité génétique. Cependant, le nombre et la position des COs entre paires de chromosomes homologues sont strictement régulés, limitant la séparation des loci en sélection variétale. Dans le cas du colza B. napus, l’utilisation d’allotriploïdes (AAC, 2n=3x=29), issus du croisement entre le colza (AACC, 2n=4x=38) et l’un de ses progéniteurs B. rapa (AA, 2n=2x=20), permet d’augmenter considérablement le nombre de COs entre chromosomes homologues A. L’objectif de cette étude était de déterminer les conséquences d’une telle variation sur la distribution des COs le long des chromosomes ainsi que d’identifier des facteurs régulant ce phénomène. Suite à la production et à la caractérisation cytogénétiques d’hybrides F1 présentant différents caryotypes, la recombinaison homologue a été évaluée par des analyses génétiques via des marqueurs SNPs physiquement ancrés sur l’ensemble duNous avons montré que l’addition du génome C chez les allotriploïdes conduit toujours à (1) la formation de COs surnuméraires, dont le nombre varie fonction des méioses mâle/femelle et du fond génétique, (2) une modification des profils de recombinaison, notamment au voisinage des centromères, et (3) une réduction de l’intensité d’interférence. De plus, nous avons révélé que le contrôle génétique de ces variations est imputé à des chromosomes C spécifiques et aurait divergé dans un contexte polyploïde. Nous avons donc identifié un levier permettant d’optimiser le brassage de la diversité génMeiotic recombination via crossovers (COs) is the main mechanism responsible for mixing genetic diversity. However, the number and position of COs between the pairs of homologous chromosomes are strictly regulated, limiting the loci separation in plant breeding. In the case of the rapeseed B. napus, the use of allotriploids (AAC, 2n=3x=29), resulting from the cross between rapeseed (AACC, 2n=4x=38) and one of its progenitors B. rapa (AA, 2n=2x=20), allows a substantial increase of the number of COs between homologous A chromosomes. The objective of this study was to determine the consequences of such a variation on the distribution of COs along the chromosomes and to identify factors regulating this phenomenon. Following the production and cytogenetic characterization of F1 hybrids with different karyotypes, homologous recombination was assessed by genetic analyzes via SNPs markers physically anchored on the whole A genome.We showed that the additional C genome in allotriploids always leads to (1) the formation of extra COs, for which the number depends on the male/female meiosis and the genetic background, (2) the modification of the recombination landscapes, especially in the vicinity of centromeres, and (3) the decrease of CO interference. In addition, we revealed that the genetic control of these variations is assigned to specific C chromosomes and could have evolved in a polyploid context. We have therefore identified a way to optimize the shuffling of genetic diversity in rapeseed breeding

Impact du niveau de ploïdie et de l’évolution des génomes sur le contrôle de la fréquence et de la distribution des évènements de recombinaison chez les Brassicas

Meiotic recombination via crossovers (COs) is the main mechanism responsible for mixing genetic diversity. However, the number and position of COs between the pairs of homologous chromosomes are strictly regulated, limiting the loci separation in plant breeding. In the case of the rapeseed B. napus, the use of allotriploids (AAC, 2n=3x=29), resulting from the cross between rapeseed (AACC, 2n=4x=38) and one of its progenitors B. rapa (AA, 2n=2x=20), allows a substantial increase of the number of COs between homologous A chromosomes. The objective of this study was to determine the consequences of such a variation on the distribution of COs along the chromosomes and to identify factors regulating this phenomenon. Following the production and cytogenetic characterization of F1 hybrids with different karyotypes, homologous recombination was assessed by genetic analyzes via SNPs markers physically anchored on the whole A genome.We showed that the additional C genome in allotriploids always leads to (1) the formation of extra COs, for which the number depends on the male/female meiosis and the genetic background, (2) the modification of the recombination landscapes, especially in the vicinity of centromeres, and (3) the decrease of CO interference. In addition, we revealed that the genetic control of these variations is assigned to specific C chromosomes and could have evolved in a polyploid context. We have therefore identified a way to optimize the shuffling of genetic diversity in rapeseed breeding.La recombinaison méiotique via les Crossing-Overs (COs) est le principal mécanisme permettant le brassage de la diversité génétique. Cependant, le nombre et la position des COs entre paires de chromosomes homologues sont strictement régulés, limitant la séparation des loci en sélection variétale. Dans le cas du colza B. napus, l’utilisation d’allotriploïdes (AAC, 2n=3x=29), issus du croisement entre le colza (AACC, 2n=4x=38) et l’un de ses progéniteurs B. rapa (AA, 2n=2x=20), permet d’augmenter considérablement le nombre de COs entre chromosomes homologues A. L’objectif de cette étude était de déterminer les conséquences d’une telle variation sur la distribution des COs le long des chromosomes ainsi que d’identifier des facteurs régulant ce phénomène. Suite à la production et à la caractérisation cytogénétiques d’hybrides F1 présentant différents caryotypes, la recombinaison homologue a été évaluée par des analyses génétiques via des marqueurs SNPs physiquement ancrés sur l’ensemble duNous avons montré que l’addition du génome C chez les allotriploïdes conduit toujours à (1) la formation de COs surnuméraires, dont le nombre varie fonction des méioses mâle/femelle et du fond génétique, (2) une modification des profils de recombinaison, notamment au voisinage des centromères, et (3) une réduction de l’intensité d’interférence. De plus, nous avons révélé que le contrôle génétique de ces variations est imputé à des chromosomes C spécifiques et aurait divergé dans un contexte polyploïde. Nous avons donc identifié un levier permettant d’optimiser le brassage de la diversité gé

La distribution des évènements de crossing-over, un paramètre modulable chez les Brassicas

Meiotic recombination by Crossover (CO) is the primary mechanism for the genetic mixing of diversity in the production of offspring in breeding programs. However, the number and distribution of COs are strictly regulated. Indeed, there is still a CO per chromosome, but rarely more and their distribution is not uniform along the chromosome. Yet in Brassicas, it is possible to increase by a factor of 6 the rate of recombination between the genomes A in AAC triploid hybrid (2n = 29) compared with the AA diploid (2n = 20), due to the nature of C chromosomes in addition, particularly to the C9. It is now possible to make a physical connection with these changes in the frequency of recombination with the recent sequencing of the genomes of B. rapa and B. napus. The purpose of this study is to understand how the genomic structure of chromosome A07 determines the formation of COs and to determine the effect of the addition of C9 chromosome and the 9 chromosomes C in a diploid AA on COs distribution. To make this, we have (1) selected three areas contrasted for the frequency of recombination on chromosome A07 on AA, AA+1C9 and AAC populations, and (2) densified and mapped microsatellite markers physically anchored every 300 Kb to characterize these areas. We have shown that the distribution of COs along chromosome A07 is explained by the genomic structure in AA diploid. New points of recombination occur in the presence of C9 chromosome and 9 chromosome C in cold regions in the AA control and especially in pericentromeric regions. These findings offer the prospect of breaking some linkage disequilibrium and stir retained loci in plant breeding.La recombinaison méiotique, par l'intermédiaire de crossing-over (CO) est le principal mécanisme permettant le brassage génétique de la diversité lors de la production de descendance dans les programmes de sélection variétale. Cependant, le nombre et la répartition des COs sont strictement régulés. En effet, il existe toujours un CO par chromosome mais très rarement plus et leur distribution n'est pas homogène le long des chromosomes. Pourtant, chez les Brassicas, il est possible d'augmenter d'un facteur 6 le taux de recombinaison entre les génomes A chez les hybrides triploïdes AAC (2n=29) par rapport aux diploïdes AA (2n=20), grâce à la nature des chromosomes C en addition et notamment du chromosome C9. Les séquençages récents des génomes de B. rapa et de B. napus permettent désormais de faire le lien physique avec ces variations de la fréquence de recombinaison. L'objectif de cette étude est donc de comprendre comment la structure génomique du chromosome A07 conditionne la formation des COs et de déterminer l'effet de l'addition du chromosome C9 et des 9 chromosomes C chez un diploïde AA sur leur distribution. Nous avons pour ce faire (1) choisi 3 zones contrastées pour la fréquence de recombinaison sur le chromosome A07 chez les populations AA, AA+1C9 et AAC et (2) densifié puis cartographié des marqueurs microsatellites physiquement ancrés tous les 300 Kb pour caractériser ces zones. Nous avons ainsi montré que la distribution des COs le long du chromosome A07 est expliquée par sa structure génomique chez des diploïdes AA. De nouveaux points de recombinaison apparaissent en présence du chromosome C9 et des 9 chromosomes C dans des régions froides chez le témoin AA et notamment dans les régions péricentromériques. Ces résultats offrent ainsi la perspective de pouvoir briser certains déséquilibres de liaison et de brasser ces locus conservés en sélection variétale

Améliorer la recombinaison méiotique pour une exploitation optimale de la diversité chez le colza Brassica napus L.

National audienceMeiotic recombination through crossovers (COs) is the key mechanism for generating genetic diversity in plant breeding programs. However, the number and position of COs between the pairs of homologous chromosomes are strictly regulated, preventing to generate many allelic combinations in progenies. A major challenge is to overcome these constraints for enhancing genetic shuffling. In the case of the rapeseed B. napus, the use of allotriploids (AAC, 2n=3x=29), resulting from the cross between rapeseed (AACC, 2n=4x=38) and its B. rapa progenitor (AA, 2n=2x=20), could allow to disrupt the recombination rules. Indeed, a substantial increase of the number of COs was identified between one pair of A homologs compared to AA and AACC hybrids. The objective of this study was to extend at the whole A genome the COs boost in allotriploids AAC and to determine the consequences of such a variation on the distribution of COs along the chromosomes. Following the production and cytogenetic characterization of AA (2n=2x=20) and AAC (2n=3x=29) hybrids (Fig. 1), we assessed homologous recombination from nearly 3,000 COs obtained per progeny by using SNP markers well distributed along the A genome (1 SNP per ~1.25 Mbp). Compared to the diploid, the allotriploid showed 3.4 times more overall COs with extra COs between each pair of homologous A chromosomes (Fig. 2). Most surprisingly, we found that such a rise was associated with dramatic changes in the shape of recombination landscapes with COs all along the A chromosomes, even in the vicinity of centromeres that are normally deprived of COs in diploids and in most studied species (Fig. 3). These results offer the opportunity for geneticists and plant breeders to dramatically enhance the generation of new diversity and to optimize the introgression of agronomical traits of interest from B. rapa into B. napus (Fig. 4).La recombinaison méiotique est le principal outil du sélectionneur pour brasser la diversité génétique entre deux parents mais le nombre et la distribution des Crossing-Overs (COs) sont strictement contrôlés. L’objectif de ce travail a été de préciser comment modifier ces règles tout en exploitant la diversité des espèces apparentées chez le colza (Brassica napus, AACC, 2n=4x=38), un allotétraploïde issu de l’hybridation naturelle entre la navette (B. rapa, AA, 2n=2x=20) et le chou (B. oleracea, CC, 2n=2x=18). Par des analyses génétiques conduites sur des descendances d’hybrides (Fig. 1), nous montrons qu’exploiter un intermédiaire allotriploïde AAC (2n=3x=29), résultant du croisement entre le colza et la navette, permet d’augmenter considérablement le nombre des COs entre chaque paire d’homologues (Fig. 2), et surtout que ceux-ci peuvent se former dans des régions génomiques usuellement dépourvues de COs (Fig. 3). Ces résultats démontrent qu’il est possible de modifier le déséquilibre de liaison ainsi que d’optimiser l’introgression de régions d’intérêt provenant de la navette chez le colza (Fig. 4)

Speciation success of polyploid plants closely Relates to the regulation of meiotic recombination.

International audiencePolyploidization is a widespread phenomenon, especially in flowering plants that have all undergone at least one event of whole genome duplication during their evolutionary history. Consequently, a large range of plants, including many of the world's crops, combines more than two sets of chromosomes originating from the same (autopolyploids) or related species (allopolyploids). Depending on the polyploid formation pathway, different patterns of recombination will be promoted, conditioning the level of heterozygosity. A polyploid population harboring a high level of heterozygosity will produce more genetically diverse progenies. Some of these individuals may show a better adaptability to different ecological niches, increasing their chance for successful establishment through natural selection. Another condition for young polyploids to survive corresponds to the formation of well-balanced gametes, assuring a sufficient level of fertility. In this review, we discuss the consequences of polyploid formation pathways, meiotic behavior and recombination regulation on the speciation success and maintenance of polyploid species

Interspecies sexual behaviour between a male Japanese macaque and female sika deer

International audienceInterspecies sexual behaviour or ‘reproductiveinterference’ has been reported across a wide range ofanimal taxa. However, most of these occurrences wereobserved in phylogenetically close species and weremainly discussed in terms of their effect on fitness,hybridization and species survival. The few cases ofheterospecific mating in distant species occurred betweenanimals that were bred and maintained in captivity. Onlyone scientific study has reported this phenomenon,describing sexual harassment of king penguins by anAntarctic fur seal. This is the first article to report matingbehaviour between a male Japanese macaque (Macacafuscata yakui) and female sika deer (Cervus nipponyakushimae) on Yakushima Island, Japan. Although Japanesemacaques are known to ride deer, this individualshowed clearly sexual behaviour towards several femaledeer, some of which tried to escape whilst others acceptedthe mount. This male seems to belong to a group ofperipheral males. Although this phenomenon may beexplained as copulation learning, this is highly unlikely.The most realistic hypothesis would be that of matedeprivation, which states that males with limited access tofemales are more likely to display this behaviour. Whateverthe cause for this event may be, the observation ofhighly unusual animal behaviour may be a key to understandingthe evolution of heterospecific mating behaviourin the animal kingdom

Evaluation of Mental Foramen with Cone Beam Computed Tomography: A Systematic Review of Literature

Purpose. The aim of this systematic review is to assess whether the anatomy of mental foramen is precisely evaluable with cone beam computed tomography (CBCT) before implantation in humans. Methods. A systematic review was carried out to evaluate the anatomy of mental foramen (size, position, symmetry, anterior loop, and accessory mental foramen or multiple mental foramina). According to Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, an electronic search of three databases (Medline, Web of Science, and Cochrane Library) was undertaken until June 2020 and was supplemented by manual searching. Two reviewers will independently perform the processes of study inclusion, data extraction, and quality assessment. Systematic reviews, studies about children, and case reports were excluded. Only studies using CBCT to do preoperative evaluation were selected. Results. From 728 potentially eligible articles, 72 were included in the qualitative analysis and quantitative synthesis. This systematic review provided an assessment of the anatomy of the mental foramen. The mental foramen was located mostly between the two premolars (between 50.4% and 61.95%) or apically to the second premolar (from 50.3% to 57.9%). The mean diameter of the mental foramen was bigger in males than in females; the difference between them could reach 0.62 mm. The anterior loop seemed to be longer in males (between 0.87 ± 1.81 and 7.25 ± 2.02 mm) than in females (between 0.81 ± 1.18 and 6.52 ± 1.63 mm) and with the presence of teeth (from 0.91 ± 1.18 to 2.55 ± 1.28 for dentate people and from 0.25 ± 0.61 to 2.40 ± 0.88 mm for edentate population). The anterior loop and the accessory mental foramina were detected more frequently with CBCT than panoramic X-ray: only between 0.0 and 48.6% AMFs detected with CBCT were also seen with panoramic images. Clinical Significance. The mental foramen (MF) is an important landmark for local anesthesia and surgical and implantology procedures. Its location, morphology, and anatomical variations need to be considered to avoid mental nerve injury. The aim of this review is to evaluate the mental foramen using CBCT through a systematic literature review to improve knowledge of this complex area for the clinician

Re-synthèse d’espèces : l’exemple du colza

National audienceLe colza (Brassica napus, AACC, 2n=4x=38) est une espèce allopolyploïde d'intérêt agronomique et économique majeur qui constitue un excellent modèle pour identifier la stratégie optimale afin d'introduire de la diversité génétique provenant de ses deux espèces constitutives, la navette (Brassica rapa, AA, 2n=2x=20) et le chou (Brassica oleracea, CC, 2n=2x=18). La première stratégie est de produire des formes resynthétisées par croisement des espèces diploïdes. Chez ce matériel, la première méiose est à l'origine d'une explosion de recombinaisons homéologues entre les génomes A et C qui entraînent de nombreux réarrangements, une instabilité méiotique dans la descendance et une faible fertilité. Cependant, le croisement avec le colza naturel peut permettre de modifier le dosage de certaines régions génomiques d'intérêt et de cumuler ainsi des QTL à effets forts. Pour la seconde stratégie, correspondant au croisement direct entre le colza et l'une de ses espèces constitutives, nous avons montré qu'il est possible d'augmenter le nombre et de modifier la position des crossovers entre chromosomes homologues. Cette stratégie a été exploitée pour introduire la diversité génétique présente dans les core collections des deux espèces diploïdes dans une même variété de colza. Ces deux stratégies permettent de réduite le goulot d'étranglement subi au cours de la sélection, ouvrant de nouvelles perspectives pour l'amélioration du colza