Ploidy Level Research Articles

Morphological and molecular data demonstrate the existence of Betula fruticosa and B. middendorffii and the absence of B. ovalifolia in northeastern China

Abstract Shrub birches are important components of massive wetlands in Northeast China, although much of these habitats have been lost over the past two decades. However, the taxonomy of shrub birches has been ambiguous owing to their morphological variation. In this study, we incorporated morphological and molecular data to address the taxonomic challenges associated with shrub birches. We characterized the morphological variation in the leaves, seeds, and bracts of 11 shrub birch populations in Northeast China and a population of Betula ovalifolia in northern Japan. We genotyped birch individuals from Northeast China at 15 microsatellite loci as well as a subset of individuals, using restriction site-associated DNA sequencing (RAD-seq). The populations in Northeast China consisted of B. fruticosa and B. middendorffii. These two species and B. ovalifolia differ in the width of their seed wings and the angle between the side lobes of their bracts, despite substantial intraspecific variation. Our genetic data revealed two distinct clusters, corresponding to B. fruticosa and B. middendorffii. Ploidy level assessment via RAD-seq revealed that B. fruticosa is diploid and B. middendorffii is tetraploid. Phylogenetic analysis revealed that B. fruticosa formed a sister clade to diploid B. humilis, and B. middendorffii formed a clade with diploid B. nana. Our results indicate the existence of B. fruticosa and B. middendorffii and the probable absence of B. ovalifolia in the northern Daxing’an Range, as all the tetraploid individuals sampled there represented B. middendorffii. In addition, our results suggest that B. humilis and B. nana may have served as diploid parents of the tetraploid species B. ovalifolia and B. middendorffii, respectively.

Extent and patterns of morphological and molecular genetic diversity and population structure of Nigerian Taro cultivars.

Genetic diversity is crucial for conservation efforts as well as breeding programs targeted at the development of improved varieties. Taro, a climate-resilient crop, plays a vital role in the nutritional and economic livelihoods of many households in Nigeria, but its yield is very low due to inadequate genetic improvement efforts. A diversity assessment of Nigerian taro is therefore required to create a premise for its improvement in yield, quality and disease tolerance. In this study, the genetic diversity and population structure of 490 taro cultivars comprising two main gene pools: Dasheen (215) and Eddoe (275), collected from farmers and marketers across seven states in Nigeria was assessed using 3047 Diversity Array Technology single nucleotide polymorphism (DArT-SNP) markers. A subset of 114 taro cultivars, comprising 30 Dasheens and 84 Eddoes were further phenotyped using 24 agro-morphological descriptors. Both phenotypic and molecular characterization revealed higher genetic diversity among the Eddoes than Dasheens. Estimates of gene flow (Nm = 0.353) revealed intermixing of cultivars among the States of collection, with the highest gene flow occurring between cultivars from Anambra and Ondo states and the lowest between Anambra and Kwara states. Population structure and Ward's minimum variance hierarchical cluster based on DArT-SNPs identified four groups, one comprising Dasheen and three comprising Eddoe cultivars. Hierarchical clustering based on phenotypic traits delineated three clusters. Variation between gene pools (49%) was higher than within gene pools (32%). Variation among States of collection was high (41%), while variation among individuals within gene pools (18%) and States of collection (19%) was relatively low. Correlation between phenotypic and genotypic diversity assessments was low (r = 0.01), indicating that both approaches were necessary for assessing genetic diversity in taro. However, genotypic assessment provided better information about genetic diversity of the taro cultivars. This is the first study that represented germplasm collection across the major taro growing regions of Nigeria. The findings from this study based on agro-morphological characterization and DArT-SNP genotyping are critical for genetic characterization, conservation and breeding of taro in Nigeria, mainly initiating hybridization between the two genepools after careful assessment of ploidy levels of the accessions collected in this study. This will facilitate in developing improved taro varieties with desirable traits, such as higher yield, better disease resistance, and improved nutritional quality.

The Role of Polyploidy in the Genetic Structure and Expansion of Lepisorus clathratus in the Qinghai–Tibetan Plateau and Hengduan Mountains

Polyploidy plays a crucial role in plant evolution, particularly in shaping genetic diversity and geographic distribution. This study investigates the genetic diversity and distribution of Lepisorus clathratus (C. B. Clarke) Ching, a polyploid fern species endemic to the Qinghai–Tibetan Plateau and Hengduan Mountains. We sampled 586 individuals from 66 populations and identified three ploidy levels: diploid, tetraploid, and hexaploid. Flow cytometry and chloroplast DNA sequencing were used to assess ploidy variation and genetic structure. Tetraploid populations dominated the Hengduan Mountains and exhibited wider geographic ranges, while diploids were largely confined to the Qinghai–Tibetan Plateau. Molecular variance analysis revealed significant genetic differentiation among regions, with polyploid populations demonstrating higher cross-region migration rates compared with diploids, as evidenced by the historical gene flow analysis. Ecological niche modeling suggested that polyploids expanded more successfully in post-glacial periods, likely due to their greater ecological flexibility and capacity for long-distance colonization. These findings highlight the critical role of polyploidy in shaping genetic structure and species expansion, contributing to the understanding of plant adaptation in response to historical climatic changes.

Cell cycle time in the root apical meristem of angiosperms and its dependence on holoploid DNA content.

In the angiosperm root apical meristem, the holoploid DNA content is not directly related to cell cycle time. Instead, ploidy, chromosome number, and taxa emerge as key factors that influence this interaction. It is commonly considered that cell cycle time in the angiosperm root apical meristem is directly related to the holoploid DNA content, and this is one of the manifestations of the nucleotypic effect. In this paper, we significantly expanded the previously reported data on cell cycle time using the thymidine method and the rate-of-cell-production method and investigated the nucleotypic effect in different taxonomic groups, in diploids with varying numbers of chromosomes, and in species of different ploidy levels. The nucleotypic effect was most pronounced in diploids with a chromosome number of less than 17, especially in the orders Asparagales and Liliales. In diploids with 17 and a greater number of chromosomes, and in polyploids, the nucleotypic effect was only evident in these two orders and was practically absent in the rest of angiosperms, which have generally lower the holoploid DNA content and average DNA content per chromosome. Overall, our work demonstrates that in angiosperms the relationship between cell cycle time in the root apical meristem and the holoploid DNA content is complex and not homogeneous and it is not directly related to cell cycle time. Instead, ploidy, chromosome number, and taxa emerge as key factors that influence this interaction.

Aegilops crassa Cytotypes in Some Regions of Türkiye.

A new hexaploid cytotype of Aegilops crassa has been identified in Türkiye. To assess the ploidy levels of native populations, 50 samples from Adıyaman, Batman, Bitlis, Diyarbakır, Hakkari, Mardin, Siirt, Şanlıurfa, Şırnak, and Van were analyzed using flow cytometry and cytogenetic techniques. DNA content was determined by comparison with standard plants. Results confirmed two cytotypes in Türkiye: tetraploid populations from Batman, Bitlis, Diyarbakır, Hakkari, Mardin, Siirt, Şanlıurfa, and Şırnak, and hexaploid accessions from Adıyaman and Van. Ten metaphase plates were analyzed. The tetraploid cytotype exhibited chromosome lengths of 8.95 ± 0.27 to 13.96 ± 0.13 µm, a total genome length of 165.51 ± 0.34 µm, and nuclear DNA content of 18.53 ± 0.29 to 20.37 ± 0.49 pg. Most chromosomes were metacentric, except for chromosomes 7, 8, 10, and 12, which were submetacentric. Two satellite pairs were found on chromosomes 4 and 10. The hexaploid cytotype showed chromosome lengths of 8.90 ± 0.16 to 14.06 ± 0.06 µm, a total genome length of 230.47 ± 0.23 µm, and nuclear DNA content of 33.40 ± 0.52 to 35.01 ± 0.31 pg. Most chromosomes were also metacentric, with three satellite pairs on chromosomes 3, 6, and 10. In conclusion, both tetraploid (2n = 2x = 28) and hexaploid (2n = 6x = 42) cytotypes of Ae. crassa exist in Türkiye, with the hexaploid cytotype having potential for wheat breeding programs.

Do Different Wheat Ploidy Levels Respond Differently Against Stripe Rust Infection: Interplay between Reactive Oxygen Species (ROS) and the Antioxidant Defense System?

Wheat stripe rust (Puccinia striiformis f. sp. tritici, Pst) is the most damaging wheat disease, causing substantial losses in global wheat production and productivity. Our study aimed to unravel the complex reciprocity between reactive oxygen species and the antioxidant defense system as a source of resistance against stripe rust in diploid, tetraploid and hexaploid wheat genotypes. The significant genetic variability for stripe rust in the materials under study was evident as the genotypes showed contrasting responses during both the adult and seedling stages. Our thorough perspective on the biochemical responses of wheat genotypes to stripe rust infection revealed distinct patterns in oxidative damage, antioxidant enzymes and photosynthetic pigments. Principal component analysis revealed inverse correlations between antioxidants and ROS, underscoring their key function in maintaining the cellular redox balance and protecting plants against oxidative damage. Diploid (Ae. tauschii) wild wheat exhibited a better biochemical defense system and greater resistance to stripe rust than the tetraploid (T. durum) and hexaploid (Triticum aestivum) wheat genotypes. The antioxidant enzyme activity of durum wheat was moderate compared to diploid and hexaploid wheat genotypes. The hexaploid wheat genotypes exhibited increased ROS production, reduced antioxidant enzyme activity and decreased photosynthetic pigment levels. This study enhances understanding of the antioxidant defense system across different wheat ploidies facing stripe rust, serving as a valuable strategy for improving crop disease resistance. This study validated the biochemical response of stripe rust-resistant and susceptible candidate genotypes, which will be used to develop genetic resources for discovering stripe rust resistance genes in wheat.

Comparative transcriptomic analyses of diploid and tetraploid citrus reveal how ploidy level influences salt stress tolerance.

Citrus is an important fruit crop for human health. The sensitivity of citrus trees to a wide range of abiotic stresses is a major challenge for their overall growth and productivity. Among these abiotic stresses, salinity results in a significant loss of global citrus yield. In order to find straightforward and sustainable solutions for the future and to ensure citrus productivity, it is of paramount importance to decipher the mechanisms responsible for salinity stress tolerance. Thisstudy aimed to investigate how ploidy levels influence salt stress tolerance in citrus by comparing the transcriptomic responses of diploid and tetraploid genotypes. In a previous article we investigated the physiological and biochemical response of four genotypes with different ploidy levels: diploid trifoliate orange (Poncirus trifoliata [L.] Raf.) (PO2x) and Cleopatra mandarin (Citrus reshni Hort. Ex Tan.) (CL2x) and their respective tetraploids (PO4x, CL4x). In this study, we useda multifactorial gene selection and gene clustering approach to finely dissect the influence of ploidy level on the salt stress response of each genotype. Following transcriptome sequencing, differentially expressed genes (DEGs) were identified in response to salt stress in leaves and roots of the different citrus genotypes. Gene expression profiles and functional characterization of genes involved in the response to salt stress, as a function of ploidy level and the interaction between stress response and ploidy level, have enabled us to highlight the mechanisms involved in the varieties tested. Saltstress induced overexpression of carbohydrate biosynthesis and cell wall remodelling- related genes specifically in CL4x Ploidy level enhanced oxidative stress response in PO and ion management capacity in both genotypes. Results further highlighted that under stress conditions, only the CL4x genotype up- regulated genes involved in sugar biosynthesis, transport management, cell wall remodelling, hormone signalling, enzyme regulation and antioxidant metabolism. These findings provide crucial insights that could inform breeding strategies for developing salt-tolerant citrus varieties.

FindGSEP: estimating genome size of polyploid species using k-mer frequencies.

Estimating genome size using k-mer frequencies, which plays a fundamental role in designing genome sequencing and analysis projects, has remained challenging for polyploid species, i.e., ploidy p > 2. To address this, we introduce "findGSEP," which is designed based on iterative curve fitting of k-mer frequencies. Precisely, it first disentangles up to p normal distributions by analyzing k-mer frequencies in whole genome sequencing of the focal species. Second, it computes the sizes of genomic regions related to 1∼p (homologous) chromosome(s) using each respective curve fitting, from which it infers the full polyploid and average haploid genome size. "findGSEP" can handle any level of ploidy p, and infer more accurate genome size than other well-known tools, as shown by tests using simulated and real genomic sequencing data of various species including octoploids. "findGSEP" was implemented as a web server, which is freely available at http://146.56.237.198:3838/findGSEP/. Also, "findGSEP" was implemented as an R package for parallel processing of multiple samples. Source code and tutorial on its installation and usage is available at https://github.com/sperfu/findGSEP.

Effective colchicine-induced polyploid induction in Centella asiatica (L.) Urban

Centella asiatica (L.) Urban, a tropical herb, has been used both as a vegetable and a medicinal herb. The induction of polyploidy in C. asiatica represents an alternative approach to enhance its yield through breeding. The objective of this study was to induce polyploidy in C. asiatica by treating its seeds with colchicine, with the intention to create a genetically diverse population. The seeds of C. asiatica were treated with 0.0, 0.1, 0.2, 0.3 and 0.4% colchicine for 12 and 24 h. Subsequently, the agricultural characteristics were studied. Ploidy levels were examined through flow cytometry analysis and morphological characteristics were studied. It was found that the concentrations of colchicine significantly resulted in the germination, abnormality, height, and number of leaves of 1-month old seedlings. Studies have shown that both 12 and 24 h exposure to 0.2% colchicine resulted in maximum seedling abnormalities. When the polyploidy of 5-month-old C. asiatica seedlings were examined, examination of putative tetraploid revealed that treatments treated with colchicine T4 (0.1, 24), T6 (0.2, 24) and T9 (0.4, 12) were 100% tetraploid. The study revealed that treating with 0.1, 0.2% colchicine for 24 h and 0.4% colchicine for 24 h promotes polyploidy easily and efficiently. Polyploids feature bigger leaves, longer stems, and a more intense green color.

Polyploidy linked with species richness but not diversification rates or niche breadth in Australian Pomaderreae (Rhamnaceae).

Polyploidy is an important evolutionary driver for plants and has been linked with higher species richness and increases in diversification rate. These correlations of ploidy with plant radiations could be the result of polyploid lineages exploiting greater niche space and novel niches due to their enhanced adaptability. Ploidy evolution and how it links with diversification of plants across the Australian continent is not well understood. Here, we focused on the ploidy evolution of the Australasian Rhamnaceae tribe Pomaderreae. We generated a densely-sampled phylogeny (90%, 215/240 spp.) of the tribe and used it to test for the evolution of ploidy. We obtained 30 orthologous nuclear loci per sample and dated the phylogeny using TreePL. Ploidy estimates for each sequenced species was obtained using nQuire, based on phased sequence data. We used MiSSE to obtain tip diversification rates and tested for significant relationships between diversification rates and ploidy. We also assessed for relationships between ploidy level and niche breadth, using distributional records, species distributional modelling, and WorldClim data. Polyploidy is extensive across the tribe, with almost half (45%) of species and majority of genera exhibiting this trait. We found a significant positive relationship between polyploidy and genus size (i.e., species richness), but non-significant positive relationship between polyploidy and diversification rates. Polyploidy did not result in significantly wider niche space occupancy for Pomaderreae, however polyploidy did allow for transitions into novel wetter niches. Spatially, eastern Australia is the diversification hotspot for Pomaderreae in contrast to the species hotspot of southwest Western Australia. The relationship between polyploidy and diversification is complex. Ancient polyploidisation events likely played an important role in the diversification of species rich genera. A lag time effect may explain the uncoupling of tip diversification rates and polyploidy of extant lineages. Further studies on other groups are required to validate these hypotheses.

The genetic diversity and population structure of wild and cultivated Avena species in Ethiopia using a SSR markers

Oats are grains that can be consumed by both animals and humans. They have thrived in Ethiopia, where certain oat species are considered native to the region. This work represents the first investigation of the population structure and genetic diversity of Ethiopian and other country oats. This led the scientists to explore the genetic diversity and population structure of wild and cultivated Ethiopian oats (Avena) species as well as oat cultivated in USA, the Netherlands and Austria. This study's main objective looks to be to investigate the variation in genetic makeup of cultivated and wild oat species. Studying the population structure of the oat species in the germplasm of Ethiopia, USA, the Netherlands and Austria. We used nineteen fluorescent SSR (simple sequence repeat) markers since previous research had indicated that these markers had high PIC (polymorphism information content) values. Five species of Avena were studied among the 176 oat accessions: A. sativa (cultivated oats) and four wild oats, such as A. abyssinica, A. vaviloviana, A. fatua, and A. sterilis. The AMOVA investigation revealed significant genetic distinctions among populations, individuals, and within individuals, explaining 18 % of the variance within populations, 4 % among populations, and 78 % within individuals. The AMOVA analysis of Avena species demonstrated extensive variance, with 33 % variation among species and 67 % within each species, underscoring robust species differentiation. The study also discovered gene interchange between wild oat and cultivated populations, defining two Avena species: domesticated oats and wild oats. Using the STRUCTURE software at K = 2, PCoA, and UPGMA, a distinct genetic structure was displayed in the dataset. Despite variations in ploidy levels and genomes, A. sterilis and A. vaviloviana were determined to be more closely linked, whereas A. abyssinica and A. fatua demonstrated a close association. This research delivers valuable insights for scientists and can be employed in oat breeding programs to improve future oat yield and productivity.

Exploratory analysis of agro-morphological characteristics in Nigella sativa L. plant genotypes to determine mutagen colchicine ameliorative/ non-ameliorative impacts.

This experimental study aimed to elucidate the optimal colchicine concentration for inducing polyploidy and to examine the morphological effects on Nigella sativa L. (family Ranunculaceae) plants recognized as 'Kalonji' in India. Here, seeds were exposed with different concentration of colchicine ranging from 0.025 to 0.4% with varying time duration (24-48h). The agro-morphological attributes and chromosome counts of the putative polyploids were compared with control diploid plants, revealing significant differences. The ploidy level determined by chromosome counts revealed that 0.05-0.1% concentration of colchicine induced tetraploids within both plant genotypes for 24h and 48h. However, results based on agro-morphological trait correlation analysis revealed more significant association among yield traits at 0.1% concentration and the principal component analysis revealed that the maximum possible ameliorative effect of the colchicine dose was the lowest concentration (0.025% for a 48-hour exposure time) for the AN1 genotype; likewise, a 0.05% concentration established a more positive association in terms of growth and yield attributes for the AN20 genotype. This study demonstrated that low dosages (0.025% and 0.1%) strongly impact plant growth and yield, whereas higher dosages obliterate these positive effects and add destructive characteristics within plants which ultimately reduces yield.

CDK8/19 inhibition triggers a switch from mitosis to endomitosis in cord blood megakaryocytes.

Neonatal and adult megakaryocytes differ in proliferative capacity and ploidy levels, and neonatal and adult platelets differ in function, gene expression, and protein content. The mechanisms underlying these differences are incompletely understood. CDK8 and CDK19 are transcriptional kinases part of the CDK-mediator complex, which regulates gene transcription in a cell-specific manner. We discovered that cortistatin A, a potent highly selective inhibitor of CDK8/CDK19, significantly reduced cell expansion and increased ploidy in cord blood-derived megakaryocytes. These phenotypic changes were associated with gene expression changes that partially overlapped developmentally regulated genes. These findings might have relevance for the management of developmental megakaryocyte disorders.

Light Microscopic and Scanning Electron Microscopic Techniques to Characterize Nutlets of Some Indian Cyperoideae (Cyperaceae) and Their Taxonomic Significance.

In the present investigation, nutlet morphological and micro-morphological characters were analyzed using Light Microscope (LM) and Scanning Electron Microscope (SEM) in 38 taxa under 13 genera from the sub-family Cyperoideae of Cyperaceae to find out whether these characters are taxonomically important or not. Nutlet morphology and surface characters of the representative taxa from all the possible tribes under the sub-family Cyperoideae namely, Fuireneae, Cypereae, Cariceae, Abildgaardieae, Eleocharideae, Pseudoschoeneae, Schoenoplecteae, and Sclerieae were evaluated for their taxonomic significance. Cluster analysis was employed considering nutlet morphological characters to determine the overall similarity among the taxa based on 153 character states. Except in few specified cases, grouping of the taxa in the clusters is in accordance to the taxonomic treatments made by recent Cyperologists. Nutlets in the tribe Abildgaardieae showed maximum level of variability in size, shape, and surface ornamentation at the level of higher taxon, but showed specificity at the species level. Tuberculate, striate-reticulate, and transversely wavy ridged surface ornamentations were found in different species of Fimbristylis. Previously described cryptic variation, and effect of different ploidy level were not reflected in nutlet surface morphology and micromorphology in Fimbristylis dichotoma and F. ovata complexes which was previously made the taxa taxonomically very difficult. Serrulate anticlinal wall in F. bisumbellata was the most unique in Fimbristylis. Species under the megadiverse genus Carex representing the tribe Cariceae showed very unique type of surface ornamentation. Surface walls of all the studied species of Carex were characterized by polygonal epidermal cells with single conical silica body (2-3 per cell in C. speciosa) of variable length and sizes. Most interestingly, in C. nubigena, presence of the central silica body and peripheral satellites was not consistent. Based on the presence and absence, two different variants under the species were identified. In C. nubigena, when silica body was present, epidermal cells were characterized by central conical silica body surrounded by variable number of satellites. The present investigation first time reports this novel nutlet surface character in C. nubigena. Among the studied characters, length and height of conical, height of apex, and width of apex are variable among Carex species. On the other hand, exclusion of the genera Schoenoplectiella and Schoenoplectus from tribe Scirpeae s.l. and placement under the tribes Pseudoschoeneae and Schoenoplecteae (respectively) was also supported by the present investigation. The present study also confirms that nutlet morphological and micro-morphological characters are useful in identification and arrangement of different taxa under the subfamily Cyperoideae of Cyperaceae. Result of the present investigation was correlated and discussed in comparative manner with the treatments of the recent past.

One Hundred Years of Progress and Pitfalls: Maximising Heterosis through Increasing Multi-Locus Nuclear Heterozygosity.

The improvement in quantitative traits (e.g., yield, size) in F1 offspring over parent lines is described as hybrid vigour, or heterosis. There exists a fascinating relationship between parental genetic distance and genome dosage (polyploidy), and heterosis effects. The contribution of nuclear heterozygosity to heterosis is not uniform across diploid and polyploid crops, even within same species, thus demonstrating that polyploid crops should be part of any discussion on the mechanisms of heterosis. This review examines the records of correlating heterosis with parental genetic distance and the influence of adding supplementary genomes in wide crosses. Increasing nuclear heterozygosity through parental genetic distance has been shown to be an imperfect predictor for heterosis in a variety of commercial crops such as maize, rice, and pepper. However, increasing the ploidy level raises the maximum number of alleles that can be harboured at any one locus, and studies on crops such as oilseed rape, potato, alfalfa, maize, and rice have demonstrated that heterosis may be maximised upon increasing multi-locus nuclear heterozygosity. The novel heterotic phenotypes observed above the diploid level will contribute to our understanding on the mechanisms of heterosis and aid plant breeders in achieving the righteous goal of producing more food with fewer inputs.

An efficient and easy-to-use protocol for induction of haploids in cucumber through parthenogenic embryo development

BackgroundCucumber (Cucumis sativus L.) is a model crop to study cell biology, including the development of haploids and doubled haploids in vegetable crops. In plant breeding, haploid and doubled haploids are valuable tools for developing pure homozygous inbred lines and accelerating genetic progress by reducing the time required for breeding cycles. Besides, the haploids are also valuable in genomic studies. We are reporting the induction of haploids in cucumber involving gynoecious and parthenocarpic genotypes for the first time. This study aimed to assess the efficient induction of haploids through pollination with gamma-irradiated pollen in cucumber. The effect of gamma irradiation dose on pollen viability and germination, fruit setting percentage, seed development, and haploid embryo development in cucumber hybrid genotypes were studied in detail. The goal was to utilize this information to produce haploid plants for genomics and transformation works in this model vegetable crop.ResultsPollination was done on six cucumber genotypes using varying doses of gamma rays (100, 200, 300, 400, and 500 Gy). Genotypes, doses of irradiation, and embryo developmental stage influenced the successful generation of in-vitro haploid plants. The optimal timeframe for embryo rescue was found to be 25 to 30 days after pollination. Haploid embryos were effectively induced using irradiated pollen at 400 to 500 Gy doses. Parthenogenetic plantlets were analyzed, and their ploidy level was confirmed through stomatal physiology, cytology (mitosis), and flow cytometry methods.ConclusionThrough parthenogenic embryo development, it is possible to induce a large number of haploids in cucumber. This technique’s power lies in its ability to streamline the breeding process, enhance genetic gain, and produce superior cultivars that contribute to sustainable agriculture and food security.

Alternating between even and odd ploidy levels switches on and off the recombination control, even near the centromeres.

Meiotic recombination is a key biological process in plant evolution and breeding, as it generates genetic diversity in each generation through the formation of crossovers (COs). However, due to their importance in genome stability, COs are highly regulated in frequency and distribution. We previously demonstrated that this strict regulation of COs can be modified, both in terms of CO frequency and distribution, in allotriploid Brassica hybrids (2n = 3x = 29; AAC) resulting from a cross between Brassica napus (2n = 4x = 38; AACC) and Brassica rapa (2n = 2x = 20; AA). Using the recently updated B. napus genome now including pericentromeres, we demonstrated that COs occur in these cold regions in allotriploids, as close as 375 kb from the centromere. Reverse transcription quantitative PCR (RT-qPCR) of various meiotic genes indicated that Class I COs are likely involved in the increased recombination frequency observed in allotriploids. We also demonstrated that this modified recombination landscape can be maintained via successive generations of allotriploidy (odd ploidy level). This deregulated meiotic behavior reverts to strict regulation in allotetraploid (even ploidy level) progeny in the second generation. Overall, we provide an easy way to manipulate tight recombination control in a polyploid crop.

First successful inducing gynogenesis in Crassostrea angulata by inactivated tetraploid Crassostrea gigas sperm

Artificial induction of gynogenesis is widely practiced in aquatic animals. However, there have been few reports of obtaining adult gynogenetic marine bivalves. This study established a new and effective method for inducing gynogenesis in C. angulata using inactivated tetraploid C. gigas sperm, ultimately obtaining gynogenetic diploids. The optimal induction conditions were as follows: sperm were irradiated with ultraviolet light (254 nm) at an intensity of 1035 μW/cm2 for 60 s before fertilization with the eggs. Fifteen minutes post-fertilization, zygotes were treated with cytochalasin B (0.5 mg/L) for a duration of 20 min under a condition of 28 °C. Six different ploidy levels (2n, 3n, 4n, 5n, 6n and aneuploid) of larvae were found by karyotype analysis and flow cytometry methods, with a diploid rate of 63.57 ± 2.80 % and an induction efficiency of 7.47 ± 0.33 %. At 6 months after fertilization, induced progenies of 4 different ploidy levels (2n, 3n, 4n and aneuploid) were examined from 3 replicate groups. The proportions of diploids, triploids, tetraploids and aneuploids were 31.67 ± 3.68 %, 57 ± 3.74 %, 7.67 ± 0.94 % and 3.67 ± 0.94 %, respectively. Diploidy was determined by microsatellite analysis, which did not contain any paternal genes, suggesting them as true gynogenetic progenies. The growth traits (shell length, width, height and whole weight) of the gynogenetic diploids did not show any significant difference (P < 0.05) compared to the control diploids. Meanwhile, triploids demonstrated a significant advantage in growth. Gynogenetic diploids underwent sexual differentiation and consisted of females (31.40 ± 1.52 %), males (67.67 ± 2.75 %), and hermaphrodites (0.93 ± 1.31 %). Interestingly, the gonads of diploids developed well and produced functional gametes. This research provides robust technical support for chromosome engineering breeding and the creation of pure lines of bivalves.

Genome-wide analysis tracks the emergence of intraspecific polyploids in Phragmites australis

Polyploidization plays an important role in plant speciation and adaptation. To address the role of polyploidization in grass diversification, we studied Phragmites australis, an invasive species with intraspecific variation in chromosome numbers ranging from 2n = 36 to 144. We utilized a combined analysis of ploidy estimation, phylogeny, population genetics and model simulations to investigate the evolution of P. australis. Using restriction site-associated DNA sequencing (RAD-seq), we conducted a genome-wide analysis of 88 individuals sourced from diverse populations worldwide, revealing the presence of six distinct intraspecific lineages with extensive genetic admixture. Each lineage was characterized by a specific ploidy level, predominantly tetraploid or octoploid, indicative of multiple independent polyploidization events. The population size of each lineage has declined moderately in history while remaining large, except for the North American native and the US Land types, which experienced constant population size contraction throughout their history. Our investigation did not identify direct association between polyploidization events and grass invasions. Nonetheless, we observed octoploid and hexaploid lineages at contact zones in Romania, Hungary, and South Africa, suggestively due to genomic conflicts arising from allotetraploid parental lineages.

The size of viable pollen is correlated with ploidy level, as evidenced by a polyploid series of &lt;i&gt;Ocimum&lt;/i&gt; L. from Thailand

The size of viable pollen is correlated with ploidy level, as evidenced by a polyploid series of &lt;i&gt;Ocimum&lt;/i&gt; L. from Thailand