Mature Pollen Research Articles

Epigenetic histone H3 phosphorylation marks discriminate between univalent- and bivalent-forming chromosomes during canina asymmetrical meiosis.

Dogroses (Rosa sect. Caninae) are mostly pentaploid, bearing 2n = 5x = 35 chromosomes in somatic cells. They evolved a unique form of asymmetrical meiosis characterized by two types of chromosomes: (1) chromosomes forming bivalents and distributed in the normal sexual way; and (2) chromosomes occurring as univalents and transferred by a female gamete only. In the mature pollen of pentaploid species, seven bivalent-derived chromosomes are transmitted to offspring, and 21 unpaired univalent chromosomes are eliminated during microsporogenesis. To discriminate between bivalent- and univalent-forming chromosomes, we studied histone H3 phosphorylation patterns regulating meiotic chromosome condensation and segregation. We analysed histone modification patterns during male canina meiosis in two representative dogrose species, 5x Rosa canina and 5x Rosa rubiginosa, by immunohistochemical and molecular cytogenetics approaches. Immunostaining of meiotic cells included α-tubulin, histone H3 phosphorylation (H3S10p, H3S28p and H3T3p) and methylation (H3K4me3 and H3K27me3) marks. In addition, fluorescent in situ hybridization was carried out with an 18S rDNA probe. In the first meiotic division, univalent chromosomes underwent equational division into chromatids, while homologues in bivalents were segregated as regular dyads. In diakinesis, bivalent chromosomes displayed strong H3 phosphorylation signals in proximal regions, spreading to the rest of the chromosome. In contrast, in univalents, the H3 phosphorylation signals were weaker, occurring mostly outside proximal regions largely overlapping with the H3K4me3 signals. Reduced phosphorylation was associated with relative under-condensation of the univalent chromosomes, particularly at early diakinesis. We hypothesize that the absence of pairing and/or recombination in univalent chromosomes negatively affects the histone H3 phosphorylation of their chromatin and perhaps the loading of meiotic-specific cohesins. This apparently destabilizes cohesion of sister chromatids, leading to their premature split in the first meiotic division.

Transcriptomics reveals a core transcriptional network of K-type cytoplasmic male sterility microspore abortion in wheat (Triticum aestivum L.)

BackgroundCytoplasmic male sterility (CMS) plays a crucial role in hybrid production. K-type CMS, a cytoplasmic male sterile line of wheat with the cytoplasms of Aegilops kotschyi, is widely used due to its excellent characteristics of agronomic performance, easy maintenance and easy restoration. However, the mechanism of its pollen abortion is not yet clear.ResultsIn this study, wheat K-type CMS MS(KOTS)-90-110 (MS line) and it’s fertile near-isogenic line MR (KOTS)-90-110 (MR line) were investigated. Cytological analysis indicated that the anthers of MS line microspore nucleus failed to divide normally into two sperm nucleus and lacked starch in mature pollen grains, and the key abortive period was the uninucleate stage to dinuclear stage. Then, we compared the transcriptome of MS line and MR line anthers at these two stages. 11,360 and 5182 differentially expressed genes (DEGs) were identified between the MS and MR lines in the early uninucleate and binucleate stages, respectively. Based on GO enrichment and KEGG pathways analysis, it was evident that significant transcriptomic differences were “plant hormone signal transduction”, “MAPK signaling pathway” and “spliceosome”. We identified 17 and 10 DEGs associated with the IAA and ABA signal transduction pathways, respectively. DEGs related to IAA signal transduction pathway were downregulated in the early uninucleate stage of MS line. The expression level of DEGs related to ABA pathway was significantly upregulated in MS line at the binucleate stage compared to MR line. The determination of plant hormone content and qRT-PCR further confirmed that hormone imbalance in MS lines. Meanwhile, 1 and 2 DEGs involved in ABA and Ethylene metabolism were also identified in the MAPK cascade pathway, respectively; the significant up regulation of spliceosome related genes in MS line may be another important factor leading to pollen abortion.ConclusionsWe proposed a transcriptome-mediated pollen abortion network for K-type CMS in wheat. The main idea is hormone imbalance may be the primary factor, MAPK cascade pathway and alternative splicing (AS) may also play important regulatory roles in this process. These findings provided intriguing insights for the molecular mechanism of microspore abortion in K-type CMS, and also give useful clues to identify the crucial genes of CMS in wheat.

Content of fixed and volatile oils of pollen grains of five male cultivar of date palm Phoenix dactylifera L.

This study was conducted on the pollen of five male date palm cultivars to determine their content of fixed and volatile oils. Male cultivars were selected: Ghanamy Akhder, Ghanamy Ahmar, khukri, Wardi and Smesmi. Mature pollens were taken before their covers were cracked and the pollen extraction process was performed. The volatile oils were extracted using the Clevenger device, and the fixed oils were extracted using the Sexolate device. The results of the study showed that the male variety of , Ghanamy Ahmar was significantly superior to the rest of the varieties in the content of fixed oils, while the male variety of Wardi recorded the lowest rate, and the varieties of Ghanamy Akhder, khukri, and Smesmi did not differ in their content of fixed oils. As for volatile oils, the results of the study showed that the male variety, Ghanami Akhdar, was significantly superior to the rest of the male varieties, and recorded the highest rate . While the male variety, Wardi, recorded the lowest rate of pollen content of essential oils, The other male varieties did not differ among themselves in terms of the essential oil content of their pollen grains. The results of the study also showed the difference between the male varieties in terms of the qualitative characteristics of the oils in terms of density and refractive index.

Heat-responsive microRNAs participate in regulating the pollen fertility stability of CMS-D2 restorer line under high-temperature stress

Anther development and pollen fertility of cytoplasmic male sterility (CMS) conditioned by Gossypium harknessii cytoplasm (CMS-D2) restorer lines are susceptible to continuous high-temperature (HT) stress in summer, which seriously hinders the large-scale application of "three-line" hybrids in production. Here, integrated small RNA, transcriptome, degradome, and hormone profiling was performed to explore the roles of microRNAs (miRNAs) in regulating fertility stability in mature pollens of isonuclear alloplasmic near-isogenic restorer lines NH and SH under HT stress at two environments. A total of 211 known and 248 novel miRNAs were identified, of which 159 were differentially expressed miRNAs (DEMs). Additionally, 45 DEMs in 39 miRNA clusters (PmCs) were also identified, and most highly expressed miRNAs were significantly induced in SH under extreme HT, especially four MIR482 and six MIR6300 family miRNAs. PmC28 was located in the fine-mapped interval of the Rf1 gene and contained two DEMs, gra-miR482_L-2R + 2 and gma-miR2118a-3p_R + 1_1ss18TG. Transcriptome sequencing identified 6281 differentially expressed genes, of which heat shock protein (HSP)-related genes, such as HSP70, HSP22, HSP18.5-C, HSP18.2 and HSP17.3-B, presented significantly reduced expression levels in SH under HT stress. Through integrating multi-omics data, we constructed a comprehensive molecular network of miRNA–mRNA–gene-KEGG containing 35 pairs of miRNA/target genes involved in regulating the pollen development in response to HT, among which the mtr-miR167a_R + 1, tcc-miR167c and ghr-miR390a, tcc-miR396c_L-1 and ghr-MIR169b-p3_1ss6AG regulated the pollen fertility by influencing ARF8 responsible for the auxin signal transduction, ascorbate and aldarate metabolism, and the sugar and lipid metabolism and transport pathways, respectively. Further combination with hormone analysis revealed that HT-induced jasmonic acid signaling could activate the expression of downstream auxin synthesis-related genes and cause excessive auxin accumulation, followed by a cascade of auxin signal transduction, ultimately resulting in pollen abortion. The results provide a new understanding of how heat-responsive miRNAs regulate the stability of fertility restoration for CMS-D2 cotton under heat stress.

Pollen Development and Stainability in Vicia faba L. and Lupinus angustifolius L.

Commercially, leguminous crops (Fabaceae) are the second most important group of cultivated plants, just after grasses (Poaceae). This study focuses on the analysis of pollen development and stainability in two species belonging to the Fabaceae family: Vicia faba L. and Lupinus angustifolius L. Morphological analysis of the anthers at various stages of flower development allowed us to trace the processes of microsporogenesis and microgametogenesis. Nine different cell staining protocols with diverse mechanisms of action, including acetocarmine, Alexander’s dye, aniline blue in lactophenol, Calcein AM, FDA, MTT, TTC, Lugol’s iodine, and aceto-orcein, were tested for their suitability in assessing the viability of microspores as well as pollen grains in both species. Among the applied dyes, four allowed for the discrimination between viable and nonviable microspores in V. faba, and six dyes allowed for this in L. angustifolius. For mature pollen grains, all dyes enabled differentiation between viable and nonviable cells in both species. The highest viability indications for V. faba microspores were obtained with acetocarmine (94.6%), while for mature pollen, aniline blue in lactophenol, MTT, and aceto-orcein yielded the highest viability indications (90.8–96.3%). In L. angustifolius, the highest percentages of viable microspores (64.9–66.5%) were obtained with the acetocarmine, aniline blue in lactophenol, and TTC dyes. For mature pollen, the highest viability indications (83.4%–92.9%) were obtained with acetocarmine, aniline blue in lactophenol, Lugol’s iodine, and aceto-orcein. The viability of V. faba pollen grains in an in vitro germination test showed that the highest pollen germination (61.3%) was observed on the BK medium (rich in minerals with 10% sucrose). In L. angustifolius, the highest pollen germination was observed on the media containing boric acid and 5% sucrose (70.5%) and on the medium containing 10% sucrose only (74.2%).

Xylan clustering on the pollen surface is required for exine patterning.

Xylan is a crosslinking polymer that plays an important role in the assembly of heterogeneous cell wall structures in plants. The pollen wall, a specialized cell wall matrix, exhibits diverse sculpted patterns that serve to protect male gametophytes and facilitate pollination during plant reproduction. However, whether xylan is precisely anchored into clusters and its influence on pollen wall patterning remain unclear. Here, we report xylan clustering on the mature pollen surface in different plant species that is indispensable for the formation of sculpted exine patterns in dicot and monocot plants. Chemical composition analyses revealed that xylan is generally present at low abundance in the mature pollen of flowering plants and shows plentiful variations in terms of substitutions and modifications. Consistent with the expression profiles of their encoding genes, genetic characterization revealed IRREGULAR XYLEM10-LIKE (IRX10L) and its homologous proteins in the GT47 family of glycosyltransferases as key players in the formation of these xylan micro-/nano-compartments on the pollen surface in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa). A deficiency in xylan biosynthesis abolished exine patterning on pollen and compromised male fertility. Therefore, our study outlines a mechanism of exine patterning and provides a tool for manipulating male fertility in crop breeding.

Plastid Inheritance Revisited: Emerging Role ofOrganelle DNA Degradation inAngiosperms.

Plastids are essential organelles in angiosperms and show non-Mendelian inheritance due to their evolution as endosymbionts. In approximately 80% of angiosperms, plastids are thought to be inherited from the maternal parent, whereas other species transmit plastids biparentally. Maternal inheritance can be generally explained by the stochastic segregation of maternal plastids after fertilization because the zygote is overwhelmed by the maternal cytoplasm. In contrast, biparental inheritance shows the transmission of organelles from both parents. In some species, maternal inheritance is not absolute and paternal leakage occurs at a very low frequency (∼10-5). A key process controlling the inheritance mode lies in the behavior of plastids during male gametophyte (pollen) development, with accumulating evidence indicating that the plastids themselves or their DNAs are eliminated during pollen maturation or at fertilization. Cytological observations in numerous angiosperm species have revealed several critical steps that mutually influence the degree of plastid transmission quantitatively among different species. This review revisits plastid inheritance from a mechanistic viewpoint. Particularly, we focus on a recent finding demonstrating that both low temperature and plastid DNA degradation mediated by the organelle exonuclease DEFECTIVE IN POLLEN ORGANELLE DNA DEGRADATION1 (DPD1) influence the degree of paternal leakage significantly in tobacco. Given these findings, we also highlight the emerging role of DPD1 in organelle DNA degradation.

Introduction of barnase/barstar in soybean produces a rescuable male sterility system for hybrid breeding.

Hybrid breeding for increased vigour has been used for over a century to boost agricultural outputs without requiring higher inputs. While this approach has led to some of the most substantial gains in crop productivity, breeding barriers have fundamentally limited soybean (Glycine max) from reaping the benefits of hybrid vigour. Soybean flowers self-pollinate prior to opening and thus are not readily amenable to outcrossing. In this study, we demonstrate that the barnase/barstar male sterility/rescue system can be used in soybean to produce hybrid seeds. By expressing the cytotoxic ribonuclease, barnase, under a tapetum-specific promoter in soybean anthers, we are able to completely block pollen maturation, creating male sterile plants. We show that fertility can be rescued in the F1 generation of these barnase-expressing lines when they are crossed with pollen from plants that express the barnase inhibitor, barstar. Importantly, we found that the successful rescue of male fertility is dependent on the relative dosage of barnase and barstar. When barnase and barstar were expressed under the same tapetum-specific promoter, the F1 offspring remained male sterile. When we expressed barstar under a relatively stronger promoter than barnase, we were able to achieve a successful rescue of male fertility in the F1 generation. This work demonstrates the successful implementation of a biotechnology approach to produce fertile hybrid offspring in soybean.

MYB transcription factors and their roles in the male reproductive development of flowering plants

As one of the largest transcription factor families with complex functional differentiation in plants, the MYB transcription factors (MYB TFs) play important roles in the physiological and biochemical processes of plant growth and development. Male reproductive development, an essential part of sexual reproduction in flowering plants, is undoubtedly regulated by MYB TFs. In this review, we summarize the roles of the MYB TFs involved in the three stages of male reproductive development: pollen grains formation and maturation, filament elongation and anther dehiscence, and fertilization. Also, the potential downstream target genes and upstream regulators of these MYB TFs are discussed. Furthermore, we propose the underlying regulatory mechanisms of these MYB TFs: (1) A complex network of MYB TFs regulates various aspects of male reproductive development; (2) MYB homologous genes in different species may be functionally conserved or differentiated; (3) MYB TFs often form regulatory complexes with bHLH TFs.

DDM1-mediated R-loop resolution and H2A.Z exclusion facilitates heterochromatin formation in Arabidopsis.

Programmed constitutive heterochromatin silencing is essential for eukaryotic genome regulation, yet the initial step of this process is ambiguous. A large proportion of R-loops (RNA:DNA hybrids) had been unexpectedly identified within Arabidopsis pericentromeric heterochromatin with unknown functions. Through a genome-wide R-loop profiling screen, we find that DDM1 (decrease in DNA methylation 1) is the primary restrictor of pericentromeric R-loops via its RNA:DNA helicase activity. Low levels of pericentromeric R-loops resolved by DDM1 cotranscriptionally can facilitate constitutive heterochromatin silencing. Furthermore, we demonstrate that DDM1 physically excludes histone H2A variant H2A.Z and promotes H2A.W deposition for faithful heterochromatin initiation soon after R-loop clearance. The dual functions of DDM1 in R-loop resolution and H2A.Z eviction are essential for sperm nuclei structure maintenance in mature pollen. Our work unravels the cotranscriptional R-loop resolution coupled with accurate H2A variants deposition is the primary step of constitutive heterochromatin silencing in Arabidopsis, which might be conserved across eukaryotes.

Transcriptomic Insight into the Pollen Tube Growth of Olea europaea L. subsp. europaea Reveals Reprogramming and Pollen-Specific Genes Including New Transcription Factors.

The pollen tube is a key innovation of land plants that is essential for successful fertilisation. Its development and growth have been profusely studied in model organisms, but in spite of the economic impact of olive trees, little is known regarding the genome-wide events underlying pollen hydration and growth in this species. To fill this gap, triplicate mRNA samples at 0, 1, 3, and 6 h of in vitro germination of olive cultivar Picual pollen were analysed by RNA-seq. A bioinformatics R workflow called RSeqFlow was developed contemplating the best practices described in the literature, covering from expression data filtering to differential expression and clustering, to finally propose hub genes. The resulting olive pollen transcriptome consisted of 22,418 reliable transcripts, where 5364 were differentially expressed, out of which 173 have no orthologue in plants and up to 3 of them might be pollen-specific transcription factors. Functional enrichment revealed a deep transcriptional reprogramming in mature olive pollen that is also dependent on protein stability and turnover to allow pollen tube emergence, with many hub genes related to heat shock proteins and F-box-containing proteins. Reprogramming extends to the first 3 h of growth, including processes consistent with studies performed in other plant species, such as global down-regulation of biosynthetic processes, vesicle/organelle trafficking and cytoskeleton remodelling. In the last stages, growth should be maintained from persistent transcripts. Mature pollen is equipped with transcripts to successfully cope with adverse environments, even though the in vitro growth seems to induce several stress responses. Finally, pollen-specific transcription factors were proposed as probable drivers of pollen germination in olive trees, which also shows an overall increased number of pollen-specific gene isoforms relative to other plants.

Genome-wide identification and expression analyses of the pectate lyase (PL) gene family in Fragaria vesca

BackgroundPectate lyase (PL, EC 4.2.2.2), as an endo-acting depolymerizing enzyme, cleaves α-1,4-glycosidic linkages in esterified pectin and involves a broad range of cell wall modifications. However, the knowledge concerning the genome-wide analysis of the PL gene family in Fragaria vesca has not been thoroughly elucidated.ResultsIn this study, sixteen PLs members in F. vesca were identified based on a genome-wide investigation. Substantial divergences existed among FvePLs in gene duplication, cis-acting elements, and tissue expression patterns. Four clusters were classified according to phylogenetic analysis. FvePL6, 8 and 13 in cluster II significantly contributed to the significant expansions during evolution by comparing orthologous PL genes from Malus domestica, Solanum lycopersicum, Arabidopsis thaliana, and Fragaria×ananassa. The cis-acting elements implicated in the abscisic acid signaling pathway were abundant in the regions of FvePLs promoters. The RNA-seq data and in situ hybridization revealed that FvePL1, 4, and 7 exhibited maximum expression in fruits at twenty days after pollination, whereas FvePL8 and FvePL13 were preferentially and prominently expressed in mature anthers and pollens. Additionally, the co-expression networks displayed that FvePLs had tight correlations with transcription factors and genes implicated in plant development, abiotic/biotic stresses, ions/Ca2+, and hormones, suggesting the potential roles of FvePLs during strawberry development. Besides, histological observations suggested that FvePL1, 4 and 7 enhanced cell division and expansion of the cortex, thus negatively influencing fruit firmness. Finally, FvePL1-RNAi reduced leaf size, altered petal architectures, disrupted normal pollen development, and rendered partial male sterility.ConclusionThese results provide valuable information for characterizing the evolution, expansion, expression patterns and functional analysis, which help to understand the molecular mechanisms of the FvePLs in the development of strawberries.

A single-nucleotide substitution of CjTKPR1 determines pollen production in the gymnosperm plant Cryptomeria japonica.

Pollinosis, also known as pollen allergy or hay fever, is a global problem caused by pollen produced by various plant species. The wind-pollinated Japanese cedar (Cryptomeria japonica) is the largest contributor to severe pollinosis in Japan, where increasing proportions of people have been affected in recent decades. The MALE STERILITY 4 (MS4) locus of Japanese cedar controls pollen production, and its homozygous mutants (ms4/ms4) show abnormal pollen development after the tetrad stage and produce no mature pollen. In this study, we narrowed down the MS4 locus by fine mapping in Japanese cedar and found TETRAKETIDE α-PYRONE REDUCTASE 1 (TKPR1) gene in this region. Transformation experiments using Arabidopsis thaliana showed that single-nucleotide substitution ("T" to "C" at 244-nt position) of CjTKPR1 determines pollen production. Broad conservation of TKPR1 beyond plant division could lead to the creation of pollen-free plants not only for Japanese cedar but also for broader plant species.

Ontogeny of Different Tetrad Types in the Single Microsporangium of Mitrephora tomentosa (Annonaceae)

Annonaceae, comprising approximately 107 genera and 2400 species, is the largest family among early-divergent Magnoliales. Previous studies have concentrated on the binding mechanism that holds together the four members of tetrads in Annonaceae. However, the development mechanisms of different tetrad types remain largely unknown. Mitrephora tomentosa was found to exhibit five permanent tetrad types, with two or three of them existing in the same microsporangium, which is ideal for studying the formation mechanisms of different permanent tetrad pollens in a single microsporangium and explaining the relationship between cytokinesis and pollen tetrad types. The ontogenetic development of the different tetrads in M. tomentosa was investigated using electron microscopy technologies, histochemical staining, and immunocytochemistry. During meiosis, pollen mother cells produce decussate and tetragonal tetrads by successive cytokinesis and produce tetrahedral and rhomboidal tetrads by simultaneous cytokinesis. Bidirectional callose deposition was observed in tetrahedral, tetragonal, rhomboidal, and decussate tetrads. The variations in the process of microsporogenesis randomly accumulate and manifest as different combinations of cytokinesis and callose deposition, leading to the formation of differently shaped tetrads. In mature permanent tetrad pollens, four microspores are connected by both simple cohesion and cytoplasmic channels, which also play an important role in maintaining the synchronization of the tetrad members.

MBD3 Regulates Male Germ Cell Division and Sperm Fertility in Arabidopsis thaliana.

DNA methylation plays important roles through the methyl-CpG-binding domain (MBD) to realize epigenetic modifications. Thirteen AtMBD proteins have been identified from the Arabidopsis thaliana genome, but the functions of some members are unclear. AtMBD3 was found to be highly expressed in pollen and seeds and it preferably binds methylated CG, CHG, and unmethylated DNA sequences. Then, two mutant alleles at the AtMBD3 locus were obtained in order to further explore its function using CRISPR/Cas9. When compared with 92.17% mature pollen production in the wild type, significantly lower percentages of 84.31% and 78.91% were observed in the mbd3-1 and mbd3-2 mutants, respectively. About 16-21% of pollen from the mbd3 mutants suffered a collapse in reproductive transmission, whereas the other pollen was found to be normal. After pollination, about 16% and 24% of mbd3-1 and mbd3-2 mutant seeds underwent early or late abortion, respectively. Among all the late abortion seeds in mbd3-2 plants, 25% of the abnormal seeds were at the globular stage, 31.25% were at the transition stage, and 43.75% were at the heart stage. A transcriptome analysis of the seeds found 950 upregulated genes and 1128 downregulated genes between wild type and mbd3-2 mutants. Some transcriptional factors involved in embryo development were selected to be expressed, and we found significant differences between wild type and mbd3 mutants, such as WOXs, CUC1, AIB4, and RGL3. Furthermore, we found a gene that is specifically expressed in pollen, named PBL6. PBL6 was found to directly interact with AtMBD3. Our results provide insights into the function of AtMBD3 in plants, especially in sperm fertility.

Comparative transcriptome analysis reveals the involvement of an MYB transcriptional activator, SmMYB108, in anther dehiscence in eggplant.

Male sterility is a highly attractive agronomic trait as it effectively prevents self-fertilization and facilitates the production of high-quality hybrid seeds in plants. Timely release of mature pollen following anther dehiscence is essential for stamen development in flowering plants. Although several theories have been proposed regarding this, the specific mechanism of anther development in eggplant remains elusive. In this study, we selected an R2R3-MYB transcription factor gene, SmMYB108, that encodes a protein localized primarily in the nucleus by comparing the transcriptomics of different floral bud developmental stages of the eggplant fertile line, F142. Quantitative reverse transcription polymerase chain reaction revealed that SmMYB108 was preferentially expressed in flowers, and its expression increased significantly on the day of flowering. Overexpression of SmMYB108 in tobacco caused anther dehiscence. In addition, we found that SmMYB108 primarily functions as a transcriptional activator via C-terminal activation (amino acid 262-317). Yeast one-hybrid and dual-luciferase reporter assays revealed that genes (SmMYB21, SmARF6, and SmARF8) related to anther development targeted the SmMYB108 promoter. Overall, our results provide insights into the molecular mechanisms involved in the regulation of anther development by SmMYB108.

Microsporogenesis, microgametogenesis, and pollen grain morphology of Fouquieria fasciculata (Fouquieriaceae, Ericales)

Background: Embryology of the male reproductive structures in Fouquieriaceae has been poorly studied. The ontogeny of the anther wall, microsporogenesis, microgametogenesis, and pollen morphology were described in detail for Fouquieria fasciculata.
 Questions: How microsporogenesis and microgametogenesis are carried out in Fouquieria fasciculata? How is the morphology of mature pollen grain?
 Study species: Fouquieria fasciculata (Fouquieriaceae).
 Study site and date: Río Estórax Canyon, near the El Plátano, Querétaro, Mexico.
 Methods: Floral buds and flowers at different stages of development were collected and processed for further analysis with light and scanning electron microscopy.
 Results: The development of the anther wall is of Dicotyledonous type. The anther wall consists of a single-layered epidermis covered by a thick cuticle, an endothecium with U-shaped fibrous thickenings, one middle layer and a secretory tapetum with uni or binucleate cell. Two orbicules types were characterized: doughnut-shape orbicules and aggregated orbicules with ruminate appearance. Microsporogenesis is successive, the microspore tetrads are tetrahedral. Pollen grains are prolate, tricolporate with reticulate-heterobrochate exine, and are shed in the two-celled stage.
 Conclusions: This research is the first comprehensive study of male structures ontogeny of Fouquieriaceae. Remarkable features were described in Fouquieria fasciculata, such as the differentiation of a secretory tapetum and the presence of orbicules, which are described for the first time and contribute to characterize the embryology of Fouquieriaceae.

Multi-omics research on common allergens during the ripening of pollen and poplar flocs of Populus deltoides.

Populus deltoides is widely cultivated in China and produces a large number of pollen and poplar flocs from March to June per year. Previous studies have found that the pollen of P. deltoides contains allergens. However, studies on the ripening mechanism of pollen/poplar flocs and their common allergens are very limited. Proteomics and metabolomics were used to study the changes of proteins and metabolites in pollen and poplar flocs of P. deltoides at different developmental stages. Allergenonline database was used to identify common allergens in pollen and poplar flocs at different developmental stages. Western blot (WB) was used to detect the biological activity of common allergens between mature pollen and poplar flocs. In total, 1400 differently expressed proteins (DEPs) and 459 different metabolites (DMs) were identified from pollen and poplar flocs at different developmental stages. KEGG enrichment analysis showed that DEPs in pollen and poplar flocs were significantly enriched in ribosome and oxidative phosphorylation signaling pathways. The DMs in pollen are mainly involved in aminoacyl-tRNA biosynthesis and arginine biosynthesis, while the DMs in poplar flocs are mainly involved in glyoxylate and dicarboxylate metabolism. Additionally, 72 common allergens were identified in pollen and poplar flocs at different developmental stages. WB showed that there were distinct binding bands between 70 and 17KD at the two groups of allergens. A multitude of proteins and metabolites are closely related to the ripening of pollen and poplar flocs of Populus deltoides, and they contain common allergens between mature pollen and poplar flocs.

Selective sweeps identification in distinct groups of cultivated rye (Secale cereale L.) germplasm provides potential candidate genes for crop improvement

BackgroundDuring domestication and subsequent improvement plants were subjected to intensive positive selection for desirable traits. Identification of selection targets is important with respect to the future targeted broadening of diversity in breeding programmes. Rye (Secale cereale L.) is a cereal that is closely related to wheat, and it is an important crop in Central, Eastern and Northern Europe. The aim of the study was (i) to identify diverse groups of rye accessions based on high-density, genome-wide analysis of genetic diversity within a set of 478 rye accessions, covering a full spectrum of diversity within the genus, from wild accessions to inbred lines used in hybrid breeding, and (ii) to identify selective sweeps in the established groups of cultivated rye germplasm and putative candidate genes targeted by selection.ResultsPopulation structure and genetic diversity analyses based on high-quality SNP (DArTseq) markers revealed the presence of three complexes in the Secale genus: S. sylvestre, S. strictum and S. cereale/vavilovii, a relatively narrow diversity of S. sylvestre, very high diversity of S. strictum, and signatures of strong positive selection in S. vavilovii. Within cultivated ryes we detected the presence of genetic clusters and the influence of improvement status on the clustering. Rye landraces represent a reservoir of variation for breeding, and especially a distinct group of landraces from Turkey should be of special interest as a source of untapped variation. Selective sweep detection in cultivated accessions identified 133 outlier positions within 13 sweep regions and 170 putative candidate genes related, among others, to response to various environmental stimuli (such as pathogens, drought, cold), plant fertility and reproduction (pollen sperm cell differentiation, pollen maturation, pollen tube growth), and plant growth and biomass production.ConclusionsOur study provides valuable information for efficient management of rye germplasm collections, which can help to ensure proper safeguarding of their genetic potential and provides numerous novel candidate genes targeted by selection in cultivated rye for further functional characterisation and allelic diversity studies.

A Rapid Alkalinization Factor-like Peptide EaF82 Impairs Tapetum Degeneration during Pollen Development through Induced ATP Deficiency.

In plants, the timely degeneration of tapetal cells is essential for providing nutrients and other substances to support pollen development. Rapid alkalinization factors (RALFs) are small, cysteine-rich peptides known to be involved in various aspects of plant development and growth, as well as defense against biotic and abiotic stresses. However, the functions of most of them remain unknown, while no RALF has been reported to involve tapetum degeneration. In this study, we demonstrated that a novel cysteine-rich peptide, EaF82, isolated from shy-flowering 'Golden Pothos' (Epipremnum aureum) plants, is a RALF-like peptide and displays alkalinizing activity. Its heterologous expression in Arabidopsis delayed tapetum degeneration and reduced pollen production and seed yields. RNAseq, RT-qPCR, and biochemical analyses showed that overexpression of EaF82 downregulated a group of genes involved in pH changes, cell wall modifications, tapetum degeneration, and pollen maturation, as well as seven endogenous Arabidopsis RALF genes, and decreased proteasome activity and ATP levels. Yeast two-hybrid screening identified AKIN10, a subunit of energy-sensing SnRK1 kinase, as its interacting partner. Our study reveals a possible regulatory role for RALF peptide in tapetum degeneration and suggests that EaF82 action may be mediated through AKIN10 leading to the alteration of transcriptome and energy metabolism, thereby causing ATP deficiency and impairing pollen development.