Initiation Of Embryogenesis Research Articles

Corrigendum: 5-azacytidine promotes microspore embryogenesis initiation by decreasing global DNA methylation, but prevents subsequent embryo development in rapeseed and barley

Corrigendum: 5-azacytidine promotes microspore embryogenesis initiation by decreasing global DNA methylation, but prevents subsequent embryo development in rapeseed and barley

Stress-Induced Autophagy Is Essential for Microspore Cell Fate Transition to the Initial Cell of Androgenesis.

The isolated microspores can be reprogrammed towards embryogenesis via stress treatment during in vitro culture, and produce (doubled) haploid plants as a breeding source of new genetic variability. However, the mechanism underlying the cell fate transition from gametogenesis to embryogenesis remains largely unknown. Here, we report that autophagy plays a key role in cell fate transition for microspore embryogenesis (referred to as androgenesis) in Nicotiana tabacum. Immunofluorescence and transmission electronic microscopy detection unveiled that autophagy was triggered in microspores following exposure to inductive stress, and a transient wave of the numerous autophagy-related genes (ATGs) expression occurred before the initiation of microspore embryogenesis. Suppression or promotion of the original autophagy levels could inhibit microspore embryogenesis, indicating that stress-induced autophagic homeostasis is essential for cell fate transition. Furthermore, quantitative proteomics analysis revealed that autophagy might be involved in lignin biosynthesis and chromatin decondensation for promoting reprogramming for androgenesis initiation. Altogether, we reveal an essential role of autophagy in the microspore cell fate transition and androgenesis initiation, providing novel insight for understanding this critical developmental process.

Enhancing in vitro regeneration via somatic embryogenesis and Fusarium wilt resistance of Egyptian cucumber (Cucumis sativus L.) cultivars

BackgroundSomatic embryogenesis offers a reliable method for cucumber (Cucumis sativus L.) regeneration and genetic enhancement against Fusarium wilt. This study aimed to establish a tailored somatic embryogenesis system for Egyptian cultivars, fostering genetic improvements and Fusarium wilt-resistance lines. ResultsEmploying the Optimal Arbitrary Design (OAD) approach, we optimized the induction medium, initiating prolific embryogenic calli (53.3 %) at 1 mg/L 2,4-D. The cotyledonary leaf (CL) was the preferred explant, showing 60 % embryogenic callus development. Bieth Alpha exhibited higher responsiveness, generating ∼ 18 somatic embryos per explant compared to Prince's ∼ 10. Somatic embryogenesis system validation used quantitative RT-PCR, showing Cucumis sativus splicing factor 3B subunit (CUS1) and an embryogenesis marker gene expression exclusively within embryogenic calli and mainly during embryogenesis initiation. Evaluating fungal toxin filtrate concentrations for selecting embryogenic calli, the S2 selection (25 % filtrate, four subculture cycles) was chosen for somatic embryo development. To gauge the ramifications of selection at the genetic stratum, an in-depth analysis was executed. A cluster analysis grounded in ISSR banding patterns revealed a distinct separation between in vivo-cultivated plants of the two cultivars and regenerated plants devoid of pathogen filtrate treatment or those regenerated post-filtrate treatment. This segregation distinctly underscores the discernible genetic impact of the selection process. ConclusionsThe highest embryogenic capacity (53.3%) was achieved in this study by optimizing the induction stage, which demonstrated the optimal concentrations of BA and 2,4-D for induced proembryonic masses. Moreover, consistent gene expression throughout both stages of embryogenesis suggests that our system unequivocally follows the somatic embryogenesis pathway.

Transcriptomics integrated with metabolomics reveals the effect of cold stress on rice microspores

BackgroundMicrospore culture is one of the important biotechnological tools in plant breeding. The induction of microspore embryogenesis is a critical factor that affects the yield of microspore-derived embryo productions. Cold treatment has been reported to reprogram the gametophytic pathway in various plant species. However, the exact mechanism(s) underlying the effect of cold pre-treatment of floral buds on the efficiency of ME is still not clear.ResultsIn this study, the effects of cold stress on the microspore totipotency of rice cultivar Zhonghua 11 were investigated. Our results revealed that a 10-day cold treatment is necessary for microspore embryogenesis initiation. During this period, the survival rate of microspores increased and reached a peak at 7 days post treatment (dpt), before decreasing at 10 dpt. RNA-seq analysis showed that the number of DEGs increased from 3 dpt to 10 dpt, with more downregulated DEGs than upregulated ones at the same time point. GO enrichment analysis showed a shift from ‘Response to abiotic stimulus’ at 3 dpt to ‘Metabolic process’ at 7 and 10 dpt, with the most significant category in the cellular component being ‘cell wall’. KEGG analysis of the pathways revealed changes during cold treatment. Mass spectrometry was used to evaluate the variations in metabolites at 10 dpt compared to 0 dpt, with more downregulated DEMs being determined in both GC-MS and LC-MS modes. These DEMs were classified into 11 categories, Most of the DEMs belonged to ‘lipids and lipid-like molecules’. KEGG analysis of DEMs indicates pathways related to amino acid and nucleotide metabolism being upregulated and those related to carbohydrate metabolism being downregulated. An integration analysis of transcriptomics and metabolomics showed that most pathways belonged to ‘Amino acid metabolism’ and ‘Carbohydrate metabolism’. Four DEMs were identified in the interaction network, with stearidonic acid involving in the most correlations, suggesting the potential role in microspore totipotency.ConclusionsOur findings exhibited the molecular events occurring during stress-induced rice microspore. Pathways related to ‘Amino acid metabolism’ and ‘Carbohydrate metabolism’ may play important roles in rice microspore totipotency. Stearidonic acid was identified, which may participate in the initiation of microspore embryogenesis.

The roles of a novel CDKB/KRP/FB3 cell cycle core complex in rice gametes and initiation of embryogenesis.

The cell cycle controls division and proliferation of all eukaryotic cells and is tightly regulated at multiple checkpoints by complexes of core cell cycle proteins. Due to the difficulty in accessing female gametes and zygotes of flowering plants, little is known about the molecular mechanisms underlying embryogenesis initiation despite the crucial importance of this process for seed crops. In this study, we reveal three levels of factors involved in rice zygotic cell cycle control and characterize their functions and regulation. Protein-protein interaction studies, including within zygote cells, and in vitro biochemical analyses delineate a model of the zygotic cell cycle core complex for rice. In this model, CDKB1, a major regulator of plant mitosis, is a cyclin (CYCD5)-dependent kinase; its activity is coordinately inhibited by two cell cycle inhibitors, KRP4 and KRP5; and both KRPs are regulated via F-box protein 3 (FB3)-mediated proteolysis. Supporting their critical roles in controlling the rice zygotic cell cycle, mutations in KRP4, KRP5 and FB3 result in the compromised function of sperm cells and abnormal organization of female germ units, embryo and endosperm, thus significantly reducing seed-set rate. This work helps reveal regulatory mechanisms controlling the zygotic cell cycle toward seed formation in angiosperms.

Why do hybrids turn down sex?

Asexual reproduction is ancestral in prokaryotes; the switch to sexuality in eukaryotes is one of the major transitions in the history of life. The study of the maintenance of sex in eukaryotes has raised considerable interest for decades and is still one of evolutionary biology's most prominent question. The observation that many asexual species are of hybrid origin has led some to propose that asexuality in hybrids results from sexual processes being disturbed because of incompatibilities between the two parental species' genomes. However, in some cases, failure to produce asexual F1s in the lab may indicate that this mechanism is not the only road to asexuality in hybrid species. Here, we present a mathematical model and propose an alternative, adaptive route for the evolution of asexuality from previously sexual hybrids. Under some reproductive alterations, we show that asexuality can evolve to rescue hybrids' reproduction. Importantly, we highlight that when incompatibilities only affect the fusion of sperm and egg's genomes, the two traits that characterize asexuality, namely unreduced meiosis and the initiation of embryogenesis without the incorporation of the sperm's pronucleus, can evolve separately, greatly facilitating the overall evolutionary route. Taken together, our results provide an alternative, potentially complementary explanation for the link between asexuality and hybridization.

How to Capture Thousands of Genotypes—Initiation of Somatic Embryogenesis in Norway Spruce

Somatic embryogenesis (SE) is considered the most effective method for vegetative propagation of Norway spruce (Picea abies L. Karst). When the aim is commercial production, the process needs scaling up. This includes many initiations to increase the number of available genotypes in the cryo-bank. Numerous genotypes are needed to maintain genetic diversity in reforestation and, at the same time, are a prerequisite for the efficient improvement of breeding traits. Norway spruce is also highly susceptible to Heterobasidion root rot. We analysed the data from the SE initiations of Norway spruce from six different years, including a total of 126 families and almost 13,000 initiations, and used several genetic (including allele PaLAR3B improving Heterobasidion resistance), environmental, and operational variables to explain the initiation success and the number of cryopreserved embryogenic tissue (ET). Overall, the cone collection date was the best and most comprehensive single variable for predicting the initiation success and the number of cryopreserved ET in the logistic regression models. PaLAR3B allele did not interfere with SE initiation or the cryopreservation. In the optimal scenario, according to the current data, Norway spruce cones would be collected in southern Finland during the first two weeks of July (in approximately 800 d.d. accumulation) from the seed orchard or greenhouse and delivered quickly to the laboratory, and the cones would be cold-stored for five days or less before initiations on mLM media. Lower initiation frequencies in some families can be compensated by increasing the number of explants—however, taking operational limitations into account.

Initiation of somatic embryogenesis in Pinus caribaea var. hondurensis using mature female gametophytes as explants

Due to the difficulties of harvesting immature cones in genetic breeding orchards, such as high costs and the considerable time required, this study aimed to evaluate the somatic embryogenesis (SE) initiation of Pinus caribaea var. hondurensis using the mature female gametophyte as the initial explant. The basic medium for embryogenesis initiation was composed of QL (Quoirin and Lepoivre, 1977) nutrients, sucrose, myo-inositol, glutamine, casein hydrolisate, thiamine, 2,4-D, BAP and agar. This medium was compared with DCR (Gupta and Durzan, 1985) and WV5 (Coke, 1996) media, supplemented or not with 0.1 g L−1 folic acid (FA). Afterwards, three concentrations of 2,4-D (10, 20 and 30 μM) combined or not with BAP (2, 4 and 8 μM) were tested. After 90 days the percentages of explants with embryogenic tissue (ET), embryo-like structures and oxidation were evaluated. We observed somatic tissue initiation` on mature female gametophytes. On QL medium supplemented with FA, the initiation was observed on up to 42% of female gametophytes. The combination of 10 μM 2,4-D and 4 μM BAP resulted in the highest initiation rate. The formation of ET was confirmed in all treatments by a histochemical test. Embryo-like structures developed on QL medium supplemented with FA, were first transferred to basic medium supplemented with 1.5 g L−1 AC for 30 days and finally to the same medium supplemented with 10% polyethylene glycol 3350 and 120 µM abscisic acid. The expression of SERK-1 and GER-1 genes was analyzed. SERK-1 was expressed only in the ET, while GER-1 was expressed in both the embryogenic and non-embryogenic tissues (non-ET). However, the somatic embryos studied through morphological and histochemical tests proved to be abnormal and did not develop further.

Callogenesis and Embryogenic Potential of New Superior Cocoa (Theobroma cacao L.) Genotypes Treated with Ascorbic Acid

Clonal propagation is an alternative method of maintaining the genetic purity of superior cocoa plants (Theobroma cacao L.). The somatic embryogenesis technique is likely the most effective and efficient method for plant propagation. This study aimed at investigating the callogenesis and embryogenic potential of new superior cocoa clones on culture media added with various concentrations of antioxidants and variation in the concentration of auxin hormone combined with ascorbic acid. The superior clones used in this study were MCC 01, MCC 02, Sulawesi 3, ICCRI 07, and ICCRI 09. The parameters observed in this study were percentage of embryogenic callus formation, number of secondary somatic embryos, and percentage of embryo somatic cells that develop into planlets. The addition of 2,4,5-T combined with ascorbic acid affected the initiation of cocoa secondary somatic embryogenesis. Treatment combination of ascorbic acid 100 mg.L-1 and 2,4,5-T 1 mg.L-1 had a significant effect on the initiation of secondary somatic embryogenesis of cocoa in the embryogenic callus phase (4.73%), globular embryos (2.53%), torpedo embryos (4.67%) and sprouts (0.47%). Three clones i.e ICCRI 07, Sulawesi 3 and ICCRI 09 clones showed a higher percentage (3.0%, 2.10%, and 1.80%, respectively) of embryogenic callus growth than the other clones. Meanwhile, on MCC 01 clone, all treatments did not affect the regeneration of embryogenic callus. The combination treatment of organic acid and adenine showed a low embryogenic callus response in MCC 01 and MCC 02 clones. However, MCC 02 clone also did not show a response in form of globular, torpedo, and germination phase somatic embryo regenerations. This indicates that different plant cultivars show different responses to the addition of organic acids. Treatment combinations of adenine 0.0125 mg.L-1 + ascorbic acid 100 mg.L-1 gave the best response to the regeneration of somatic embryos for the globular, torpedo, and g

Transcriptomes and DNA methylomes in apomictic cells delineate nucellar embryogenesis initiation in citrus.

Citrus nucellar poly-embryony (NPE) is a mode of sporophytic apomixis that asexual embryos formed in the seed through adventitious embryogenesis from the somatic nucellar cells. NPE allows clonal propagation of rootstocks, but it impedes citrus cross breeding. To understand the cellular processes involved in NPE initiation, we profiled the transcriptomes and DNA methylomes in laser microdissection captured citrus apomictic cells. In apomictic cells, ribosome biogenesis and protein degradation were activated, whereas auxin polar transport was repressed. Reactive oxygen species (ROS) accumulated in the poly-embryonic ovules, and response to oxidative stress was provoked. The global DNA methylation level, especially that of CHH context, was decreased, whereas the methylation level of the NPE-controlling key gene CitRWP was increased. A C2H2 domain-containing transcription factor gene and CitRWP co-expressed specifically in apomictic cells may coordinate to initiate NPE. The activated embryogenic development and callose deposition processes indicated embryogenic fate of nucellar embryo initial (NEI) cells. In our working model for citrus NPE initiation, DNA hyper-methylation may activate transcription of CitRWP, which increases C2H2 expression and ROS accumulation, triggers epigenetic regulation and regulates cell fate transition and NEI cell identity in the apomictic cells.

Optimization of Different Factors for Initiation of Somatic Embryogenesis in Suspension Cultures in Sandalwood (Santalum album L.)

Santalum album (L.) is a prized tropical tree species of high therapeutic and industrial importance. The wood of these naturally grown plants is extensively harvested to acquire therapeutically important metabolite santalol and be used for additional functions such as in wood statuette industries. Due to high demand, it is crucial to maintain a sufficient plant population. An easy protocol for establishing cell suspension culture initiated from the loose embryogenic callus mass of sandalwood was realized by shifting 6–8-week-old morphogenic calli acquired from the mature embryonic axis and cotyledon explant cultures in fluid media. The asynchronous embryogenic cultures were sloughed with clumps of flourishing cell clumps and embryos of various progressive phases along with diffident non-embryogenic tissues. The frequency of embryo proliferation was evidenced to determinethe expansion pace of embryogenic masses under diverse conditions. The intonation of initiation and creation of cell suspension was under the directive of the influence of exogenous plant growth regulators amended in the nutrient medium at different concentrations and combinations. Maximum relative growth rate (386%) and clumps/embryoids in elevated integers (321.44) were accomplished on MS nutrient medium fortified with 2.0 mg L−1 2,4-D in association with 0.5 mg L−1 BA and 30.0 g L−1 sucrose raised from mature embryonic axis-derived calli. Plantlet regeneration in higher frequency (84.43%) was evidenced on MS medium amended with 1.0 mg L−1 each of TDZ and GA3 in conjunction with 0.5 mg L−1 NAA and 20.0 g L−1 sucrose. Mature embryonic axis-derived calli were found to be constantly better than mature cotyledon-derived calli for raising profitable and reproducible cell suspension cultures. Regenerants displayed normal growth and morphology and were founded successfully in the external environment after hardening.

Regeneration and micropropagation of Meyer lemon (Citrus x meyeri) supported by polymorphism analysis via molecular markers

Meyer lemon (Citrus x meyeri) is a valuable sweet hybrid Citrus from China, renowned for its unique taste and high nutritional value. The current study aims to establish an efficient micropropagation protocol and to evaluate the potential regenerated somatic embryos induced from in vitro Meyer lemon explants. Shoot tips and epicotyl segments were inoculated in half strength Murashige and Skoog (½ MS) medium supplemented with plant growth regulators (PGRs) for multiple shoot and root induction prior to polymorphism and microscopy analysis. Benzylaminopurine (BAP) treatment at 1 mg L−1 was found optimal in the induction of multiple shoots (100% induction rate) with the average of 3.29 ± 0.2 shoots. The synergistic effects of 2 mg L−1 BAP and 1.5 mg L−1 Indole-3-acetic acid (IAA) resulted in maximum shoot regeneration frequency (100%) with an average number of 3.6 ± 0.5 shoots per explant. Woody plant medium (WPM) without PGRs exhibited the highest rooting frequency (100%) and acclimatization of in vitro plantlets yielded 82% survivability. Inter simple sequence repeat (ISSR) and start codon targeted (SCoT) markers revealed no somaclonal variation occurrences between micropropagated plantlets of five subculture cycles and mother plant. Potential indirect somatic embryogenesis was observed from epicotyl segments of in vitro germinated seedlings at an average of 7.3 ± 1.0 embryos per explant with 80% response in ½ MS with 0.5 mg L−1 thidiazuron (TDZ). Morpho-histological and scanning electron microscopy (SEM) observations confirmed the initiation and developmental features of the embryos. This study has successfully established an efficient micropropagation protocol for Meyer lemon and documented the potential initiation of indirect somatic embryogenesis.

Somatic embryogenesis as a way of Siberian pine biodiversity preservation: initiation

The article reports about the results of an experiment to initiate somatic embryogenesis in Siberian pine in 2019. The object of the study was trees from the forest seed orchards of Berdsk forestry in the Novosibirsk region. Immature cones were collected at the stage of early embryogenesis. 5 culture media compositions and 6 genotypes were tested. Intact and dissected megagametophytes were used as explants. Two stably proliferating embryogenic lines were obtained. It has been proven that the genotype and composition of the nutrient medium influence on the initiation of somatic embryogenesis. The most competent genotypes and effective nutrient media for somatic embryogenesis of Siberian pine were revealed. It has been established that dissected megagametophytes are promising to use as explants for obtaining somatic embryogenesis in Siberian pine.

Somatic Embryogenesis Initiation in Sugi (Japanese Cedar, Cryptomeria japonica D. Don): Responses from Male-Fertile, Male-Sterile, and Polycross-Pollinated-Derived Seed Explants.

This study aimed to obtain information from several embryogenic cell (EC) genotypes analyzing the factors that affect somatic embryogenesis (SE) initiation in sugi (Cryptomeria japonica, Cupressaceae) to apply them in the improvement of protocols for efficient induction of embryogenic cell lines (ECLs). The results of several years of experiments including studies on the influence of initial explant, seed collection time, and explant genotype as the main factors affecting SE initiation from male-fertile, male-sterile, and polycross-pollinated-derived seeds are described. Initiation frequencies depending on the plant genotype varied from 1.35 to 57.06%. The best induction efficiency was achieved when seeds were collected on mid-July using the entire megagametophyte as initial explants. The extrusion of ECs started approximately after 2 weeks of culture, and the establishment of ECLs was observed mostly 4 weeks after extrusion on media with or without plant growth regulators (PGRs). Subsequently, induced ECLs were maintained and proliferated on media with PGRs by 2–3-week-interval subculture routines. Although, the initial explant, collection time, and culture condition played important roles in ECL induction, the genotype of the plant material of sugi was the most influential factor in SE initiation.

Physiological and Structural Aspects of In Vitro Somatic Embryogenesis in Abies alba Mill

Initiation of somatic embryogenesis from immature zygotic embryos, long-term maintenance of embryogenic tissue in vitro or by cryopreservation, as well as maturation, of somatic embryos of Abies alba Mill. are reported in this study. For the initiation of embryogenic tissues, a DCR medium containing different types of cytokinins (1 mg.L−1) were tested. During three consecutive years, 61 cell lines were initiated out of 1308 explants, with initiation frequencies ranging between 0.83 and 13.33%. The type of cytokinin had no profound effect on the initiation frequency within one given year. Microscopic observations revealed presence of bipolar somatic embryos in all initiated embryogenic tissues. Besides the typical bipolar somatic embryos, huge polyembryonal complexes, as well as “twin” embryos, were observed. Maturation of somatic embryos occurred on a DCR medium supplemented by abscisic acid (10 mg.L−1), polyethylene glycol (PEG-4000, 7.5%) and 3% maltose. The maturation capacity was cell-line dependent. All of the four tested cell lines produced cotyledonary somatic embryos, though at different quantities, of 16 to 252 per g of fresh weight. After germination, seedlings developed, but their further growth soon stopped after the formation of a resting bud. Altogether, seven cell lines were cryopreserved, using the slow-freezing technique. After rewarming, all tested cell lines showed regrowth rates between 81.8 and 100%.

Quantification of endogenous aromatic cytokinins in Pinus radiata embryonal masses after application of heat stress during initiation of somatic embryogenesis

Short-term exposure to high temperatures modulates the aromatic cytokinin profile of radiata pine embryonal masses when measured 8 weeks after initiation. Abstract Recent research has demonstrated that cytokinins could be involved in abiotic stress responses. However, little research has been published about the role of endogenous aromatic cytokinins during these processes. Therefore, in this study, different temperature and incubation periods (23 oC, 8 weeks; 40 oC, 4 h; 50 oC, 30 min; 60 oC, 5 min) were applied during induction of radiata pine somatic embryogenesis and the aromatic cytokinin content of the resulting embryonal masses was measured. Results indicated that temperature during induction had a significant effect on the profile of most of the aromatic cytokinins detected. All tested higher temperatures than control provoked a decline in some free bases, including N6-benzyladenine, ortho-Topolin and para-Topolin. On the other hand, the values of N6-benzyladenine nucleotides, ribosides and irreversible metabolites (9G), as well as para-Topolin ribosides, increased in embryonal masses originating from 40 oC treatment. These results suggest that despite not being traditionally considered part of the stress response machinery, aromatic cytokinins might be involved in heat-stress responses during early stages of somatic embryogenesis in radiata pine.

Somatic embryogenesis in slash pine (Pinus elliottii Engelm): improving initiation of embryogenic tissues and maturation of somatic embryos

Slash pine (Pinus elliottii Engelm.) has strong adaptability, early growth and high turpentine yield, and it is widely planted in southern China. Breeding of disease-resistant varieties is an effective way to prevent and control development of pine needle brown spot on slash pine in China. Plant regeneration by somatic embryogenesis has been achieved for slash pine, but large-scale production of somatic embryos remains restricted by several factors. We tested different embryogenesis conditions from time of initiation to maturation and studied genetic stability at simple sequence repeat (SSR) loci of regenerated plants in slash pine. Immature zygotic embryos of four open-pollinated mother trees were used for initiation of somatic embryogenesis. Seed sources (families) had a significant impact on initiation of embryonal suspensor mass (ESM, p < 0.05); however, the addition of abscisic acid ABA (1–2 mg/L) and phytosulfokine PSK (0.5 mg/L) could effectively improve initiation rate by up to 36%. Seed family 27 was the most favorable female parent for ESM initiation. The production (number of somatic embryos) was significantly increased by adding ABA (5 mg/L) during suspension culture before transferring to maturation media (p < 0.05). We tested the genetic stability of 14 regenerated plants at SSR loci, and 88.9% plants with normal phenotypes were found not to have genetic variation. We clarified the somatic embryogenesis conditions suitable for slash pine and established somatic embryo maturation technology. We clarified the somatic embryogenesis conditions suitable for slash pine and established somatic embryo maturation technology by studying several related influencing factors.

Research advances on plant synthetic apomixis

Heterosis, a phenomenon in which hybrid offspring shows better performance in many aspects than either of their homozygous parents, has been widely applied for improving crop productivity and adaptability. However, progenies generated via sexual reproduction are diverse owing to the genetic recombination during meiosis, which is not conducive to the application of heterosis. Apomixis is a type of asexual reproduction through which plants can produce clonal seeds without undergoing normal meiosis and fertilization. Therefore, apomixis has been a research hotspot for a long time because of its potential in fixing heterosis. Over 400 plant species exhibit apomictic phenomena in nature, and many genes linked with apomictic loci have been discovered in various species. These genes are involved in distinct regulatory mechanisms of apomixis. Even after decades of effort, these genes have not been successfully applied for crop apomixis because of complexity of the underlying mechanisms and lack of apomictic crops in nature. Due to the apomixis of plants also can be induced artificially by allowing plants to undergo unusual meiosis and fertilization, synthetic apomixis based on reproductive mechanisms has been proposed to fix heterosis. In MiMe ( mitosis instead of meiosis ), meiotic division is completely replaced by a mitotic-like division and diploid gametes that are genetically identical to their mother are produced. MiMe is induced by the absence of genes required for the pairing and recombination of homologous chromosomes, maintenance of sister chromatid cohesionas well as for the transition of germ cells from meiosis I to II. Following normal fertilization of clonal diploid gametes, the ploidy of offspring is doubled in each generation. To achieve synthetic apomixis and obtain clonal seeds, chromosome doubling following normal fertilization must be prevented. An effective way for this prevention is the elimination of one set of chromosomes from either parent. When a plant with altered CENH3 (centromere-specific histone H3) protein is crossed with a wild-type plant, haploid progenies are induced through the elimination of chromosomes from the cenh3 mutant. Furthermore, combining MiMe plants with a genome elimination line via crossing is an effective strategy to produce clonal seeds. In addition, upon expression of BBM1 (BABY BOOM 1), which plays an important role in the initiation of embryogenesis, in the egg cell, haploid progenies are generated that produce seeds with haploid embryos following self-fertilization. Moreover, MTL (matrilineal) disruption in plants using CRISPR/Cas9 gene editing technology also can generate haploid progenies. Therefore, the combination of MiMe with BBM1 - or MTL -induced production of haploid progenies can achieve synthetic apomixis in plants and produce clonal seeds. In this review, we summarize advances in synthetic apomixis at the molecular level and discuss the improvement of synthetic apomixis as well as its potential application in crop breeding.

Early pregnancy loss: the default outcome for fertilized human oocytes.

Early pregnancy loss is by far the most frequent outcome of human reproduction. It occurs when despite the timely interaction of gametes and initiation of embryogenesis and implantation of the conceptus, pregnancy continuance fails. From a clinical perspective, early pregnancy loss represents a neglected but relevant issue because of the high incidence, the evolving and yet not fully elucidated mechanism, the possible association with other relevant medical conditions, and the potential psychological sequelae. Our growing understanding of the dialog established between the embryo and the endometrium provides new insights into the etiology of pregnancy loss. Aneuploidies as a cause of early pregnancy loss are known for a long time, but there is now evidence that endometrium is not a passive player. An active selection aimed at impeding implantation of unhealthy embryos actually occurs at the endometrial interface. The concept of selectivity is substituting the one of mere receptivity.

Effects of Genotype and Culture Conditions on Microspore Embryogenesis and Plant Regeneration in Brassica Rapa ssp. Rapa L.

Turnip is a biennial crop and, consequently, the creation of pure lines for breeding is a time-consuming process. The production of pure turnip lines using doubled haploids produced in isolated microspore culture has not been sufficiently developed. The aim of the present work was to determine some key factors inducing embryogenesis in the isolated microspore culture of turnip, as well as investigating the manners of embryo development. It was shown that the acidity of the medium is an important factor in embryo production; different optimal pH levels ranging from 6.2 to 6.6 corresponded to individual genotypes. Such factors as the cold treatment of buds and the addition of activated charcoal to the nutrient medium increased the responsiveness of all genotypes studied. The turnip variety ‘Ronde witte roodkop herfst’ demonstrated a genetic disorder in the development of microspores; namely, non-separation of some microspores from tetrads. In the in vitro culture, each of the daughter microspores developed on its own. This indicates the dependence of the possibility of embryogenesis in the turnip microspore culture on the genotype. Results suggest that the initiation of secondary embryogenesis in primary embryos leads to an increase in the proportion of doubled haploid plants.