Meiosis In Pollen Mother Cells Research Articles

[Morphological study of sexual reproductive disorders in Ligusticum chuanxiong].

Chuanxiong Rhizoma is a well-known Sichuan-specific herbal medicine. Its original plant, Ligusticum chuanxiong, has been cultivated asexually for a long time. L. chuanxiong has sexual reproductive disorders, which restricts its germplasm innovation. However, there is little research on the reproductive system of L. chuanxiong. This study is based on a comparative anatomical research approach, using morphological dissection, paraffin sectioning, staining and compression, and combined with scanning electron microscopy technology, to observe and compare the flowers, fruits, and seeds at various stages of reproductive growth of L. chuanxiong and its wild relative L. sinense. The results showed that the meiosis of pollen mother cells is abnormal in L. chuanxiong anthers, and the size and number of microspores are uneven and inconsistent in the tetrad stage. tapetum cells are not completely degenerated during anther development. During the pollen ripening stage, there are fine cracks in the anther wall, while most anthers could not release pollen normally. The surface of mature pollen grains is concave and partially deformed, and the pollens are all inactive and cannot germinate in vitro. The starch, polysaccharides, and lipids in the pollen were insufficient. The filaments of L. chuanxiong are short at the flowering stage and recurved downward. Double-hanging fruits were observed in the fruiting stage, being wrinkled; with shriveled seeds. Compared with L. sinense at the same stage, the anthers of L. sinense developed normally, and the pollen grains are vigorous and can germinate in vitro. The double-hanging fruits of L. sinense are full and normal; at the flowering period, the filaments are long and erect, significantly higher than the stigma. Mature blastocysts are visible in the ovary of both L. chuanxiong and L. sinense, and there is no significant difference in stigmas. The conclusion is that during the development of L. chuanxiong stamens, the meiosis of pollen mother cells is abnormal, and tetrad, tapetum, filament and other pollen structures develop abnormally. L. chuanxiong has the characteristic of male infertility, which is an important reason for its sexual reproductive disorders.

Karyological studies of Iranian Allium (Amaryllidaceae) species with a focus on sect. Acanthoprason. 2. Meiotic chromosomes

Meiosis in pollen mother cells (PMCs) was studied of 23 Iranian Allium species (33 accessions, 105 individuals) that belong to two subgenera and six sections. Materials of 13 species were sampled from (near) type locations. Gametic chromosome numbers, chromosome configurations at metaphase I, chiasma frequency, as well as type and percentages of abnormalities were recognized. The basic chromosome number for all taxa investigated was x = 8. Most taxa were diploid and showed eight bivalents or in rare cases two or four pairs of univalents, but in A. subakaka, A. ubipetrense and A. zagricum tetravalents also occurred. Meiosis in less than 10% of PMCs of diploid accessions was disturbed displaying lagging chromosomes, chromatid bridges, micronuclei, or unbalanced chromosome segregations, but very rarely more than one kind of irregularities were found within one dividing cell. One to three B chromosomes were found in 11 accessions, and were recognized for the first time in A. alamutense, A. elburzense and A. iranshahrii. Our data showed no correlation between the occurrence of B chromosomes and the chiasma frequency, and also no noticeable effect of habitat factors on meiotic chromosome behavior. The studied accessions of A. atroviolaceum and A. sabalense were tetraploid (n = 16) showing irregular meiosis in 20–69% of the PMCs which is regarded as sign of autopolyploidy. Since only two out of 31 investigated accessions belonging to subg. Melanocrommyum were tetraploid, we may suggest a trivial role of polyploidy in the evolution of this subgenus.

Heat stress responses vary during floret development in European spring barley cultivars.

The Poaceae, or grasses, include many agriculturally important cereal crops such as rice (Oryza sativa), maize (Zea mays), barley (Hordeum vulgare) and bread wheat (Triticum aestivum). Barley is a widely grown cereal crop used for stock feed, malting and brewing. Abiotic stresses, particularly global warming, are the major causes of crop yield losses by affecting fertility and seed set. However, effects of heat stress on reproductive structures and fertility in barley have not been extensively investigated. In this study we examined three commercial European spring barley varieties under high temperature conditions to investigate the effects on floret development. Using a combination of fertility assays, X-ray micro computed tomography, 3-dimensional modelling, cytology and immunolabelling, we observed that male reproductive organs are severely impacted by increased temperature, while the female reproductive organs are less susceptible. Importantly, the timing of stress relative to reproductive development had a significant impact on fertility in a cultivar-dependent manner, this was most significant at pollen mitosis stage with fertility ranged from 31.6-56.0% depending on cultivar. This work provides insight into how heat stress, when applied during male pollen mother cell meiosis and pollen mitosis, affects barley fertility and seed set, and also describes complementary invasive and non-invasive techniques to investigate floret development. This information will be used to identify and study barley cultivars that are less susceptible to heat stress at specific stages of floral development.

Induction of 2n pollen by colchicine during microsporogenesis to produce polyploids in herbaceous peony (Paeonia lactiflora Pall.)

Polyploid breeding is an effective way to improve ornamental traits of horticultural plants. Colchicine, an anti-mitotic agent, is widely used to induce 2n gametes in horticultural plants, allowing for the production of polyploid plants through sexual hybridization. Based on an understanding of flower bud development and meiosis in pollen mother cells (PMCs) of Paeonia lactiflora cv. ‘Fen Yu Nu’, 2n pollen were obtained by injecting different concentrations of colchicine (0.1, 0.2, 0.3, 0.4 or 0.5%) into flower buds multiple times (once, twice or three times with a 24-h interval in between). External morphology, viability and possible hybridization of colchicine-induced 2n pollen were observed. Finally, P. lactiflora cv. ‘Lian Tai’ was pollinated with colchicine-induced pollen from ‘Fen Yu Nu’. Polyploids were identified among offspring by flow cytometry, chromosome counting, and molecular assessment using simple sequence repeats (SSR). Flower bud diameter of herbaceous peony was related with meiosis in PMCs. The most suitable period to induce 2n pollen was when most PMCs were in prophase I of meiosis, and when flower buds were about 11-12 mm in diameter. The highest induced incidence (%) of 2n pollen was 47.39% following treatment with 0.4% colchicine solution injected twice. The average diameter of 2n pollen was 46.01 μm, which was 1.53-fold wider than haploid pollen. SEM results indicated that 2n pollen were considerably different from haploid pollen in terms of external shape and surface decoration, and 2n pollen were mostly spherical or with an irregular shape. Induced 2n pollen could germinate in vitro and on the stigma of the female parent, but abnormalities such as pollen tube bifurcation or thickening were observed in both germinated states. The percentage of germinated 2n pollen in vitro was 12.78%. In addition, two tetraploids (2n = 4x = 20) were obtained by 2n pollen hybridization. SSR analysis indicated that tetraploids were produced by the spontaneous fusion of 2n female gametes with colchicine-induced 2n male gametes. This indicates that colchicine did not entirely inactivate 2n pollen. The production of few polyploids may be due to the abnormal germination of 2n pollen and obstacles in ploidy hybridization. Our findings fortify the foundation for Paeonia polyploid breeding.

Low Female Gametophyte Fertility Contributes to the Low Seed Formation of the Diploid Loquat [Eriobotrya Japonica (Thunb.) Lindl.] Line H30-6.

Loquat is a widely grown subtropic fruit because of its unique ripening season, nutrient content, and smooth texture of its fruits. However, loquat is not well-received because the fruits contain many large seeds. Therefore, the development of seedless or few-seed loquat varieties is the main objective of loquat breeding. Polyploidization is an effective approach for few-seed loquat breeding, but the resource is rare. The few-seed loquat line H30-6 was derived from a seedy variety. Additionally, H30-6 was systematically studied for its fruit characteristics, gamete fertility, pollen mother cell (PMC) meiosis, stigma receptivity, in situ pollen germination, fruit set, and karyotype. The results were as follows. (1) H30-6 produced only 1.54 seeds per fruit and the fruit edible rate was 70.77%. The fruit setting rate was 14.44% under open pollination, and the other qualities were equivalent to those of two other seedy varieties. (2) The in vitro pollen germination rate was only 4.04 and 77.46% of the H30-6 embryo sacs were abnormal. Stigma receptivity and self-compatibility in H30-6 were verified by in situ pollen germination and artificial pollination. Furthermore, the seed numbers in the fruits of H30-6 did not significantly differ among any of the pollination treatments (from 1.59 ±0.14 to 2 ± 0.17). (3) The chromosome configuration at meiotic diakinesis of H30-6 was 6.87I + 9.99II + 1.07III +0.69IV +0.24V (H30-6), and a total of 89.55% of H30-6 PMCs presented univalent chromosomes. Furthermore, chromosome lagging was the main abnormal phenomenon. Karyotype analysis showed that chromosomes of H30-6 had no recognizable karyotype abnormalities leading to unusual synapsis on the large scale above. (4) The abnormal embryo sacs of H30-6 could be divided into three main types: those remaining in the tetrad stage (13.38%), those remaining in the binucleate embryo sac stage (1.41%), and those without embryo sacs (52.82%). Therefore, we conclude that the loquat line H30-6 is a potential few-seed loquat resource. The diploid loquat line H30-6 was with low gametophyte fertility, which may be driven by abnormal meiotic synapses. The low female gamete fertility was the main reason for the few seeds. This diploid loquat line provides a new possibility for breeding a few-seed loquat at the diploid level.

Development and characterization of an allooctaploid (AABBCCRR) incorporating Brassica and radish genomes via two rounds of interspecific hybridizations

Interspecific hybridization, which leads to the combination of the genomes from different species, not only contributes to speciation but also enriches the genetic stock of crops. Production of interspecific/intergenetic hybrids between Brassica species or Brassica and relative species has been a desirable goal for plant breeders and genetic researchers. In this study, we initially generated the allotetraploid Raphanobrassica (CCRR, 2n = 36) through a cross between maternal Raphanus sativus (RR, 2n = 18) and paternal Brassica oleracea (CC, 2n = 36). We then developed an allooctaploid (AABBCCRR, 2n = 72) that incorporated three Brassica subgenomes and radish genomes through crosses between the newly formed Raphanobrassica and B. juncea (AABB, 2n=36), followed by the chromosome doubling. PCR amplification of genome-specific primers and fluorescence in situ hybridization (FISH) analysis were employed to identify the true hybrids and their chromosome complements. The new allooctaploid showed a mosaic morphology of three parents and produced some seeds, despite the very low pollen stainability. The chromosome pairing and segregation of the allooctaploid were largely normal during the meiosis of pollen mother cells. So the first allooctaploid can be used as an intermediate germplasm to transfer desirable traits into Brassica crops, or as the founder for the experimental synthesis of new species.

On the Reproductive Potential in Primula veris L. (Primulaceae): Embryological Features, Pollen and Seed Viability, Genetic Diversity.

Primula veris (Primulaceae) is a valuable medicinal plant. The main characteristics for assessing the reproductive potential (embryological features; mode of reproduction; pollen and seed viability) and the genetic diversity of populations of the species from Bulgaria were studied. The anthers are tetrasporangiate. Their wall development follows the Dicotyledonous-type and consists of: epidermis, a fibrous endothecium, an ephemeral middle layer and a secretory (glandular) tapetum. After meiosis in pollen mother cells and simultaneous microsporogenesis tetrahedral tetrads are formed predominantly in the anthers. Many ovules (approximately 20) develop in the unilocular ovary and are anatropous, tenuinucellate and bitegmic. The embryo sac (ES) develops after Polygonum (monosporic)-type from the chalazal cell of linear megaspore tetrad in the ovule. After double fertilization, a Caryophyllad-type embryo and initially nuclear endosperm form. In the studied populations, high pollen viability of more than 95% was established. Extremely low viability (about 4%) of the seeds obtained from natural populations was established. The results reveal P. veris to be a predominantly amphimictic (sexually reproducing) species, although rare vegetative propagation is also observed. As a result of this study, essential data were obtained about the reproductive structures and processes and for assessing the reproductive potential of P. veris.

Obtain inter-section hybrids between Primula forbesii (Sect. Monocarpicae) and P. saxatilis (Sect. Cortusoides)

To breed excellent cultivars with prosperous fragrant flowers, long flowering period, and high resistance to hardiness, three Primula forbesii (Sect. Monocarpicae) cultivars (2n=2x=18) and P. saxatilis (Sect. Cortusoides) (2n=2x=24) were used as parents for hybridization. Fourteen progenies were obtained from three cross combinations of P. forbesii as maternal parent by embryo rescue. Eventually, 12 progenies were proved to be true hybrids (2n=2x=21) by flow cytometry, chromosome counting and amplified fragment length polymorphism analysis. All the hybrids had long lasting flowering period just like P. forbesii, and their leaf back and scapes were not covered by white powder like P. saxatilis. The hybrid progenies were more similar to their male parent P. saxatilis by phenotypes analysis. Pollen of hybrids was abnormal and the germination rates were very low (3.18%–0.23%). Phenomena such as chromosome outside the equatorial plate, lagging chromosomes, chromosome bridges, micronucleus and polyads happened during the process of pollen mother cell meiosis, resulting pollen abortion finally. The results of backcrossing with their parents as pollen donators indicated that the pollen was able to germinate on the stigma surface and pollen tubes could extend into the hybrids’ ovules. It was showed that the inter-section hybrids could be used as female parent, but could not be used as pollen donator in continuing hybridization.

Spikelet differentiation and degeneration in rice varieties with different panicle sizes

AbstractAn essential feature of modern high‐yielding rice varieties is the production of numerous spikelets, but the physiological mechanism underlying spikelet formation in these varieties remains unclear. In this study, we explored the characteristics of spikelet differentiation and degeneration and the relevant physiological characteristics of rice varieties with different panicle sizes. The regulatory effects of alternate wetting and moderate soil drying (AWMD) on spikelet formation were also measured. We determined that the high spikelet number per panicle and grain yields of large‐panicle rice varieties were primarily due to a higher number of differentiated and surviving secondary spikelets. Furthermore, shoot dry weight, plant nitrogen (N) uptake, plant N concentration, non‐structural carbohydrate (NSC) accumulation in stems, leaf area, and leaf photosynthetic rate from branch differentiation stage (BDS) to spikelet differentiation stage (SDS) were positively correlated with the number of differentiated secondary spikelets per panicle. Plant N concentration, NSC accumulation in stems, and leaf photosynthetic rate at pollen mother cell meiosis (PMC) were negatively correlated with the number of degenerated secondary spikelets. Finally, the number of differentiated secondary spikelets of Huaidao 5 (small panicle size) and Yongyou 2640 (large panicle size) varieties was promoted by 19.2% and 6.6%, and the number of degenerated secondary spikelets was reduced by 14.4% and 6.3%, respectively, under AWMD treatment compared to continuously flooded treatment. Prominent spikelet formation under AWMD resulted from the shoot dry weight, plant N uptake, plant N concentration, NSC accumulation in stems, leaf area, and leaf photosynthetic rate. Collectively, improvements in these key aboveground indices mentioned above during the BDS to SDS and the plant N concentration, NSC accumulation in stems, and leaf photosynthetic rate at the PMC stage would benefit spikelet formation by promoting differentiation and reducing degeneration of secondary spikelets, thereby enhancing yield of large‐panicle rice varieties.

Cytological and morphology characteristics of natural microsporogenesis within Camellia oleifera.

The online version contains supplementary material available at 10.1007/s12298-021-01002-5.

Chromosome behavior during meiosis in pollen mother cells from Saccharum officinarum \xd7 Erianthus arundinaceus F1 hybrids

BackgroundIn recent years, sugarcane has attracted increasing attention as an energy crop. Wild resources are widely used to improve the narrow genetic base of sugarcane. However, the infertility of F1 hybrids between Saccharum officinarum (S. officinarum) and Erianthus arundinaceus (E. arundinaceus) has hindered sugarcane breeding efforts. To discover the cause of this infertility, we studied the hybridization process from a cytological perspective.ResultsWe examined the meiotic process of pollen mother cells (PMCs) in three F1 hybrids between S. officinarum and E. arundinaceus. Cytological analysis showed that the male parents, Hainan 92–77 and Hainan 92–105, had normal meiosis. However, the meiosis process in F1 hybrids showed various abnormal phenomena, including lagging chromosomes, micronuclei, uneven segregation, chromosome bridges, and inability to form cell plates. Genomic in situ hybridization (GISH) showed unequal chromatin distribution during cell division. Interestingly, 96.70% of lagging chromosomes were from E. arundinaceus. Furthermore, fluorescence in situ hybridization (FISH) was performed using 45S rDNA and 5S rDNA as probes. Either 45S rDNA or 5S rDNA sites were lost during abnormal meiosis, and results of unequal chromosomal separation were also clearly observed in tetrads.ConclusionsUsing cytogenetic analysis, a large number of meiotic abnormalities were observed in F1. GISH further confirmed that 96.70% of the lagging chromosomes were from E. arundinaceus. Chromosome loss was found by further investigation of repeat sequences. Our findings provide insight into sugarcane chromosome inheritance to aid innovation and utilization in sugarcane germplasm resources.

Male sterile 28 encodes an ARGONAUTE family protein essential for male fertility in maize

Male sterility is a common biological phenomenon in plants and is a useful trait for hybrid seed production. Normal tapetum development is essential for viable pollen generation. Although many genes involved in tapetum differentiation and degradation have been isolated in maize, elements that regulate tapetum development during pollen mother cell (PMC) meiosis are less studied. Here, we characterized a classical male-sterile mutant male sterile 28 (ms28) in maize. The ms28 mutant had a regular male meiosis process, while its tapetum cells showed premature vacuolation at the early meiotic prophase stage. Using map-based cloning, we cloned the Ms28 gene and confirmed its role in male fertility in maize together with two allelic mutants. Ms28 encodes the ARGONAUTE (AGO) family protein ZmAGO5c, and its transcripts primarily accumulate in premeiosis anthers, with more intense signals in PMCs. Transcriptomic analysis revealed that genes related to anther development, cell division, and reproductive structure development processes were differentially expressed between the ms28 mutant and its fertile siblings. Moreover, small RNA (sRNA) sequencing revealed that the small interfering RNA (siRNA) and microRNA (miRNA) abundances were obviously changed in ms28 meiotic anthers, which indicated that Ms28 may regulate tapetal cell development through small RNA-mediated epigenetic regulatory pathways. Taken together, our results shed more light on the functional mechanisms of the early development of the tapetum for male fertility in maize.

Genome-Wide Identification of lncRNAs Involved in Fertility Transition in the Photo-Thermosensitive Genic Male Sterile Rice Line Wuxiang S.

Long non-coding RNAs (lncRNAs) act as universal regulators of various biological processes, but no genome-wide screening of lncRNAs involved in the fertility transition of the photo-thermosensitive genic male sterile (PTGMS) rice line has been reported. Here, we performed strand-specific RNA sequencing at three developmental stages of a novel PTGMS line Wuxiang S (WXS). A total of 3,948 lncRNAs were identified; 622 of these were detected as differentially expressed lncRNAs (DE-lncRNAs) between male-sterile WXS (WXS-S) and male-fertile WXS (WXS-F). A large proportion of lncRNAs differentially expressed at the stage of pollen mother cells meiosis, suggested that it may be the most critical stage for fertility transition of WXS. Furthermore, functional annotation of the cis- and trans- targets of DE-lncRNAs showed that 150 targets corresponding to 141 DE-lncRNAs were identified as involved in anther and pollen development. Moreover, computational analysis predicted 97 lncRNAs as precursors for 72 miRNAs, and 94 DE-lncRNAs as potential endogenous target mimics (eTMs) for 150 miRNAs. Finally, using the dual luciferase reporter assays, we demonstrated that two lncRNAs act as eTMs to regulate the expression of the SPL and GRF genes by competing for the shared osa-miR156 and osa-miR396, respectively. These genomic characteristics, differential expression, and interaction of lncRNAs with miRNAs and mRNAs contribute to our understanding of the roles of lncRNAs during the fertility transition in PTGMS rice lines.

Gametophyte and embryonic ontogeny: understanding the reproductive calendar of Cypripedium japonicum Thunb. (Cypripedoideae, Orchidaceae), a lady\u2019s slipper orchid endemic to East Asia

BackgroundThe genus Cypripedium L. is one of the five genera of the subfamily Cypripedioideae, members of which are commonly known as lady’s slipper orchids. Cypripedium japonicum is a perennial herb native to East Asia, specifically China, Japan, and Korea. Due to its limited distribution, the species is included in the Endangered category of the IUCN Red List.ResultsWe investigated gametophyte development, including complete embryogenesis, in C. japonicum. The complete reproductive cycle is presented based on our observations. Anther development begins under the soil, and meiosis of pollen mother cells begins 3 weeks before anthesis, possibly during early April. The megaspore mother cells develop just after pollination in early May and mature in mid–late June. The pattern of embryo sac formation is bisporic, and there are six nuclei: three forming the egg apparatus, two polar nuclei, and an antipodal cell in the mature embryo sac. Triple fertilization results in the endosperm nucleus, which degenerates when the proembryo reaches the eight-to-sixteen-cell stage.ConclusionOur overall comparisons of the features of gametophyte and embryo development in C. japonicum suggest that previous reports on the embryology of Cypripedium are not sufficient for characterization of the entire genus. Based on the available information, a reproductive calendar showing the key reproductive events leading to embryo formation has been prepared.

Effects of low temperature in spring on fertility of pollen and formation of grain number in wheat

<p indent=0mm>Grain yield and the number of grains per ear of wheat decreased under the low temperature after jointing stage. In order to explore the physiological reasons of the decrease of grains number per ear by low temperature in spring, the spring wheat variety Yangmai 16 and the semi-winter wheat variety Xumai 30 were used as tested varieties to analyze the effects of low temperature in spring on the fertility of pollen and the formation of grain numbers at the appearance of the penultimate leaf stage (5℃/–3℃, day/night), booting stage (8℃/–1℃, day/night), and anthesis stage (12℃/4℃, day/night). The results showed that low temperature at the appearance of the penultimate leaf stage and booting stage resulted in abnormal metabolism of starch and protein in the anther both at the binuclear and tri-nuclear pollen stages and delayed degradation of the tapetum. The low temperature at the booting stage caused abnormal meiosis of pollen mother cells, abnormalities in chromosome pairing, which affected the formation of male gametophyte. The abortion rate of pollen was more significantly increased under low temperature at the appearance of the penultimate leaf stage than that at the booting stage, and it was the minimum at anthesis stage. The abortion rate of pollen in Xumai 30 was higher than that in Yangmai 16. The low temperature at three stages had significant effects on the number of spikelets, the number of fertile spikelets and the number of grains per spikelet. The effect of low temperature at the appearance of the penultimate leaf stage on grains number per spikelet was the most significant. There was a significant positive correlation between the number of grains per spike and pollen fertility, which was affected by abnormal meiosis, delayed degradation of the tapetum, and undersupply of nutriment for anther development. Therefore, the decline of pollen fertility caused by low temperature in spring is the main reason for the decrease of grains number per spike.

Effects of root morphology and physiology on the formation and regulation of large panicles in rice

Abstract At present, indica/japonica hybrid rice varieties of the Yongyou series generally show high yield and large panicles, but the physiological mechanism on the formation of large panicles is not clear. It is of great significance to understand the physiological mechanism and regulation of the formation of large panicles in super high-yield rice varieties. In this study, five groups of different rice varieties with significant differences in yield levels were selected as materials to study the contribution of large panicles to rice yield, the physiological changes in roots and canopy during the panicle differentiation stage and the regulation of large panicles by panicle nitrogen fertilizer under field and pot cultivation conditions. The results showed that 1. high-yield indica/japonica hybrid rice varieties were characterized by high spikelet number per panicle and high total number of spikelets. 2. The zeatin (Z) and zeatin riboside (ZR) contents in roots and panicles from spikelet primordium differentiation (SPD) to pistil and stamen formation (PSF), root activity (root dry weight, root oxidation activity, root bleeding rate, root total absorbing surface area and root active absorbing surface area) and non-structural carbohydrate (NSC) accumulation in stems from pollen mother cell meiosis (PMC) to pollen filling (PF) were very significantly and positively correlated with spikelet number per panicle. 3. Compared with 0 N (no panicle nitrogen fertilizer), the number of spikelets per panicle and total spikelets of Yangdao 6 and Yongyou 1540, the Z + ZR contents in panicles and roots during SPD-PSF, and the root activity and NSC accumulation in stems during PMC-PF were significantly improved under LN (panicle nitrogen fertilizer at a rate of 1.2 g pot-1) and MN (panicle nitrogen fertilizer at a rate of 2.4 g pot-1). High Z + ZR contents in young panicles and roots during SPD-PSF and large amounts of root activity (root dry weight, root oxidation activity, root bleeding rate, root total absorbing surface area and root active absorbing surface area) and NSC accumulation in stems during PMC-PF were important physiological factors in the formation of large panicles in super high-yield indica/japonica hybrid rice. Improvements in the above indexes during the panicle differentiation stage are likely contribute to the formation of large panicles and the increase in rice yield.

Characterization and transcriptome analysis of a dominant genic male sterile cotton mutant

BackgroundMale sterility is an efficient trait for hybrid seed production and germplasm innovation. Until now, most studies on male sterility were on cytoplasmic and recessive genic sterility, with few on dominant genic male sterility, especially in cotton, due to lack of such mutant.ResultsWe discovered a natural male sterile (MS) Sea Island cotton (G. barbadense) mutant. Genetic analysis showed the mutation was caused by a dominant mutation in a single nuclear gene. Comparative cytological observation of anther sections from MS and wild-type (WT) uncovered cellular differences in anther at and after the tetrad stage of pollen mother cells (PMC). In the MS anthers, the outer wall of pollen grains was free of spinules, the tapetum was vacuolated and showed delayed degradation, consequently, no functional pollen grains. Comparison of transcriptomes from meiosis, tetrad, mononuclear and binuclear pollen, and pollen maturation stages identified 13,783 non-redundant differentially expressed genes (DEGs) between MS and WT. Based on the number of DEGs, analyses of enriched GO terms and KEGG pathways, it was evident that significant transcriptomic changes occurred at and after the tetrad stage, consistent with cytological observation, and that the major differences were on metabolism of starch, sucrose, ascorbate, aldarate, alanine, aspartate and glutamate, and biosynthesis of cutin, suberine and wax. WGCNA analysis identified five modules containing 920 genes highly related to anther development, especially the greenyellow module with 54 genes that was highly associated with PMC meiosis and tetrad formation. A NAC transcription factor (Gh_D11G2469) was identified as a hub gene for this module, which warrants further functional characterization.ConclusionsWe demonstrated that the MS trait was controlled by a single dominant nuclear gene and caused by delayed tapetum degradation at the tetrad stage. Comparative transcriptome analysis and gene network construction identified DEGs, enriched GO terms and metabolic pathways, and hub genes potentially associated with anther development and the MS trait. These results contribute to our understanding of dominant genic male sterility (DGMS) and provided source for innovation of cotton germplasm.

Biological characteristics and cytological studies on anther abortion of male sterile &amp;lt;italic&amp;gt;Camellia crassocolumna&amp;lt;/italic&amp;gt;

The purpose of this study was to explore the flower morphology, anther and pollen abortion time and its cytological characteristics in male sterile plants of C. crassocolumna . The flowering process, floral morphology, anther structure, meiosis and microsporogenesis of male sterile (M350) and fertile plants (M352) of C. crassocolumna were observed by stereomicroscopy, paraffin section, chromosome preparation and DAPI staining. The results showed that the wild tea plant had a perfect flower, its anthers were tetrasporangiate shaped like a butterfly, with an anther wall development of basic type. It tapetal cells were binuclear, forming secretory cells at the tetrad stage, and degrading during mononuclear pollen stage. After the meiosis I, meiosis II and cytokinesis, pollen mother cells developed into tetrahedral tetrads. Microspores were triangular, and mature pollen was two-celled. The stamens of male sterile flowers developed normally in the early stage of flower bud development, and there was no difference between sterile and fertile flowers, while in the late stage of flower bud development, filaments were curved, anthers adhered and shriveled, anthers could not release pollen. The tapetal cells of male sterile flowers were proliferation abnormally and disordly at the meiosis of stage pollen mother cells, and the degradation of tapetum was delayed during the mononuclear and binucleate pollen periods. During meiosis of pollen mother cells of male sterile flowers, there were some abnormal appearances, such as chromosome ring, lagging chromosomes, chromosome bridges, chromosomal deletion, scattered chromosomes, unequal separation, micronucleus and abnormal tetrad. In sterile plants, the microspore cytoplasm was disorder, pollen grains adhered to each other at the mononuclear stage, pollen wall crumpled and deformed, cytoplasm and nucleus of pollen were blurred, the mature pollen cells were hollow and sunken. Taken together, the floral organ morphology of male sterile plants in C. crassocolumna belongs to stamen collapse type and anther abnormality type. The development of anthers is blocked from meiosis of pollen mother cells to uninucleate pollen stage, belonging to pollen mother cell abortion type and uninucleate pollen abortion type. Mononuclear period is the main period of anther abortion. Tapetum degradation delayed, chromosomal abnormalities of pollen mother cells in meiosis, and abnormal development of microspores and pollens, might be the main reasons for anther abortion in male sterile plants of C. crassocolumna .

Global identification and analysis revealed differentially expressed lncRNAs associated with meiosis and low fertility in autotetraploid rice

BackgroundAutotetraploid rice is a useful germplasm for polyploid rice breeding. Our previous research showed that non-coding RNAs might be associated with low fertility in autotetraploid rice. However, little information is available on long non-coding RNAs (lncRNAs) involved in the low fertility of autotetraploid rice. In the present study, RNA-seq was employed to detect the differentially expressed meiosis-related lncRNAs in autotetraploid rice, and gene overexpression and knock out experiments were used to validate the potential function of candidate lncRNA.ResultsA total of 444 differentially expressed lncRNAs (DEL) were detected during anther and ovary meiosis in autotetraploid rice. Of these, 328 DEL were associated with the transposable elements, which displayed low expression levels during meiosis in autotetraploid rice. We used rapid amplification of cDNA ends (RACE) assay to validate 10 DEL and found that the lncRNAs were not assembly artifacts, and six of them were conserved in tetraploid rice. Moreover, 237 and 20 lncRNAs were associated with pollen mother cell (PMC) and embryo sac mother cell (EMC) meiosis in autotetraploid rice, respectively. The differential expressions of some meiosis-related targets and its DEL regulator, including MEL1 regulated by TCONS_00068868, LOC_Os12g41350 (meiotic asynaptic mutant 1) by TCONS_00057811 in PMC, and LOC_Os12g39420 by TCONS_00144592 in EMC, were confirmed by qRT-PCR. TCONS_00057811, TCONS_00055980 and TCONS_00130461 showed anther specific expression patterns and were found to be highly expressed during meiosis. CRISPR/Cas9 editing of lncRNA57811 displayed similar morphology compared to wild type. The overexpression of lncRNA57811 resulted in low pollen fertility (29.70%) and seed setting (33%) in rice.ConclusionThe differential expression levels of lncRNAs, associated with transposable elements and meiosis-regulated targets, might be endogenous noncoding regulators of pollen/embryo sac development that cause low fertility in autotetraploid rice. The results enhance our understanding about rice lncRNAs, and facilitate functional research in autotetraploid rice.

Flower transcriptome dynamics during nectary development in pepper (Capsicum annuum L.).

The measurement of gene expression can provide important information about gene function and the molecular basis for developmental processes. We analyzed the transcriptomes at three different developmental stages of pepper flower [sporogenous cell division, stage (B1); pollen mother cell meiosis, stage (B2); and open flower (B3)]. In the cDNA libraries for B1, B2, and B3: 82718, 77061, and 91491 unigenes were assembled, respectively. A total of 34,445 unigene sequences and 128 pathways were annotated by KEGG pathway analysis. Several genes associated with nectar biosynthesis and nectary development were identified, and 8,955, 12,182, and 23,667 DEGs were identified in the B2 vs B1, B3 vs B1, and B3 vs. B2 comparisons. DEGs were involved in various metabolic processes, including flower development, nectar biosynthesis, and nectary development. According to the RNA-seq data, all 13 selected DEGs showed similar expression patterns after q-PCR analysis. Sucrose-phosphatase, galactinol-sucrose galactosyltransferase, and sucrose synthase played very important roles in nectar biosynthesis, and CRABS CLAW could potentially be involved in mediating nectary development. A significant number of simple sequence repeat and single nucleotide polymorphism markers were predicted in the Capsicum annuum sequences. The new results provide valuable genetic information about flower development in pepper.