Meiosis In Pollen Mother Cells Research Articles

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.

Pairing and Exchanging between Daypyrum villosum Chromosomes 6V#2 and 6V#4 in the Hybrids of Two Different Wheat Alien Substitution Lines.

Normal pairing and exchanging is an important basis to evaluate the genetic relationship between homologous chromosomes in a wheat background. The pairing behavior between 6V#2 and 6V#4, two chromosomes from different Dasypyrum villosum accessions, is still not clear. In this study, two wheat alien substitution lines, 6V#2 (6A) and 6V#4 (6D), were crossed to obtain the F1 hybrids and F2 segregating populations, and the testcross populations were obtained by using the F1 as a parent crossed with wheat variety Wan7107. The chromosomal behavior at meiosis in pollen mother cells (PMCs) of the F1 hybrids was observed using a genomic in situ hybridization (GISH) technique. Exchange events of two alien chromosomes were investigated in the F2 populations using nine polymerase chain reaction (PCR) markers located on the 6V short arm. The results showed that the two alien chromosomes could pair with each other to form ring- or rod-shaped bivalent chromosomes in 79.76% of the total PMCs, and most were pulled to two poles evenly at anaphase I. Investigation of the F2 populations showed that the segregation ratios of seven markers were consistent with the theoretical values 3:1 or 1:2:1, and recombinants among markers were detected. A genetic linkage map of nine PCR markers for 6VS was accordingly constructed based on the exchange frequencies and compared with the physical maps of wheat and barley based on homologous sequences of the markers, which showed that conservation of sequence order compared to 6V was 6H and 6B > 6A > 6D. In the testcross populations with 482 plants, seven showed susceptibility to powdery mildew (PM) and lacked amplification of alien chromosomal bands. Six other plants had amplification of specific bands of both the alien chromosomes at multiple sites, which suggested that the alien chromosomes had abnormal separation behavior in about 1.5% of the PMCs in F1, which resulted in some gametes containing two alien chromosomes. In addition, three new types of chromosome substitution were developed. This study lays a foundation for alien allelism tests and further assessment of the genetic relationship among 6V#2, 6V#4, and their wheat homoeologous chromosomes.

Dynamics of Selenium uptake, speciation, and antioxidant response in rice at different panicle initiation stages

Selenium (Se) is an essential element in animals and humans, and its deficiency may cause conditions such as cardiac disease. The production of Se-enriched rice is one of the most important ways to supply Se in the human body, and thus, understanding of the mechanisms of Se-enriched rice is of great significance. A pot experiment was conducted to study the effects of Se addition on the growth, antioxidation, Se uptake and distribution, and Se speciation in three different stages of panicle initiation stage (i.e., pistil and stamen formation stage, pollen mother cell formation stage, pollen mother cell meiosis stage) and the maturity stage. The results showed that soil Se application significantly increased Se uptake in rice. Low rates of Se (<5 mg kg-1) application enhanced the plant growth and rice yield. Se speciation assays showed that SeCys and SeMet were the two main forms found in rice, of which SeMet accounted for 65.5%-100% in the ears and leaves, while SeCys accounted for 61.4%-75.6% in brown rice. SeMet was also the main Se-species found in different subcellular parts at the panicle initiation stage. However, inorganic Se was present in brown rice, mainly as Se(VI), when the soil Se addition exceeded 5 mg kg-1. Lower rates of Se (<5 mg kg-1) promoted the antioxidant capacity, while high levels of Se (≥5 mg kg-1) reduced the antioxidant capacity of rice. The results indicate that Se effects are dose dependent, and the suitable amount of soil Se application for Se-enriched rice production would be <5 mg kg-1.

Water-Saving Traits Can Protect Wheat Grain Number Under Progressive Soil Drying at the Meiotic Stage: A Phenotyping Approach

In wheat, water deficit during meiosis of pollen mother cells greatly reduces seed set and grain number. A promising option to avoid grain losses and maintain wheat productivity under water stress is to exploit conservative water-use strategies during reproduction. In this work, two cultivars known to be adapted to different environments were studied. Water stress, with or without a polymer spray known to reduce stomatal conductance, was applied to both cultivars just prior to meiosis. Two experiments were carried out in a phenotyping platform to (1) assess and validate daily non-destructive estimation of projected leaf area and to (2) evaluate different water-use (WU) strategies across the meiotic period and their effect on physiology and yield components. Gladius displays an elevated breakpoint (BP) in the regression of WU against fraction of transpirable soil water (FTSW) for both daily and night-time WU suggesting higher conservative whole-plant response when compared to Paragon. At the same time, Gladius maintained flag leaf gas-exchange with a significant reduction at ~ 0.2 FTSW only, suggesting an uncoupled mechanism of WU reduction that optimized the water resource available for flag leaf gas-exchange maintenance. Under progressive soil drying, seed set and grain number of tillers stressed at GS41 were significantly reduced in Paragon (p < 0.05) thus leading to lower grain yield and grain number at plant level than Gladius. Polymer-induced reduction of transpiration is potentially useful when applied to the non-conservative stressed Paragon, maintaining higher FTSW, water-use efficiency and RWC during the progressive soil drying treatment. This led to better seed set (p < 0.05) and grain number maintenance (p < 0.05) than in the stressed Paragon control. We conclude that the different conservative traits detected in this work, protect grain development around meiosis and therefore maintain grain number under water-limiting conditions. Additionally, non-conservative genotypes (often with a greater expected yield potential) can be protected at key stages by reducing their water use with a polymer spray. Thus, future efforts can integrate both crop breeding and management strategies to achieve drought-resilience during the early reproductive phase in wheat and potentially other cereals.

Salicylic acid reverses pollen abortion of rice caused by heat stress

BackgroundExtremely high temperatures are becoming an increasingly severe threat to crop yields. It is well documented that salicylic acid (SA) can enhance the stress tolerance of plants; however, its effect on the reproductive organs of rice plants has not been described before. To investigate the mechanism underlying the SA-mediated alleviation of the heat stress damage to rice pollen viability, a susceptible cultivar (Changyou1) was treated with SA at the pollen mother cell (PMC) meiosis stage and then subjected to heat stress of 40 °C for 10 d until 1d before flowering.ResultsUnder control conditions, no significant difference was found in pollen viability and seed-setting rate in SA treatments. However, under heat stress conditions, SA decreased the accumulation of reactive oxygen species (ROS) in anthers to prevent tapetum programmed cell death (PCD) and degradation. The genes related to tapetum development, such as EAT1 (Eternal Tapetum 1), MIL2 (Microsporeless 2), and DTM1 (Defective Tapetum and Meiocytese 1), were found to be involved in this process. When rice plants were exogenously sprayed with SA or paclobutrazol (PAC, a SA inhibitor) + H2O2 under heat stress, a significantly higher pollen viability was found compared to plants sprayed with H2O, PAC, or SA + dimethylthiourea (DMTU, an H2O2 and OH· scavenger). Additionally, a sharp increase in H2O2 was observed in the SA or PAC+ H2O2 treatment groups compared to other treatments.ConclusionWe suggest that H2O2 may play an important role in mediating SA to prevent pollen abortion caused by heat stress through inhibiting the tapetum PCD.

Production of pollenless triploid lily hybrids from Lilium pumilum DC. × ‘Brunello’

Embryo rescue was employed to create four pollenless Asiatic triploid lily hybrids, ‘PB1’, ‘PB2’, ‘PB3’ and ‘PB4’, from the cross of Lilium pumilum DC. (2n = 2x = 24) and the Asiatic lily cultivar ‘Brunello’ (2n = 4x = 48). Cytological observation confirmed that all four hybrids were triploid (2n = 3x = 36) and that the progeny and their parents all shared the 3B karyotype. Some abnormal behavior was observed in the triploid hybrids during pollen mother cell meiosis, including chromosome bridges, lagging chromosomes, micronuclei and unequal separation. The hybrids ‘PB1’ and ‘PB2’ had malformed anthers that were pollenless and could not release pollen grains, but the other two hybrids, ‘PB3’ and ‘PB4’, had a few pollen grains in anthers that were almost normal in shape. The stem diameter, leaf index, inner perianth length, outer perianth length and flower diameter of the four hybrids were all intermediate between the respective traits of the parents. However, plant height, stem diameter and flower number per plant were superior in hybrid plants compared to both parents. Flower color, hairs on bud, flower direction and tepal shape showed wide segregation among the hybrids. Hybrid ‘PB2’ was also fragrant. The four triploid hybrids can be used as garden plants directly or as new genetic resources for breeding pollenless lily cultivars.

Nodes protect against drought stress in rice (Oryza sativa) by mediating hydraulic conductance

The importance of rice resistance to abiotic stress has largely been attributed to signal-induced closure of stomata, protection of antioxidase enzymes, and osmotic adjustment of sugars, etc. However, regulation role of nodes in water flow under drought stress has not been reported. Two rice genotypes Z4 and its recombinant inbred line (RIL) were subjected to drought stress for 10 d at the pollen mother cell meiosis stage. Results indicated a higher decline in spikelet fertility was found in RIL than Z4 plants under drought stress compared with the corresponding control. However, the leaves of Z4 plants were wilting 1 d earlier than those of RIL plants under drought stress. Accordingly, a greater decline in the RWC and water potential of the leaf and sheath, but a lower decrease in the panicle, was observed in the Z4 plants than the RIL plants. In the process, higher decrease in transpiration rate of leaf, hydraulic conductance, diameter of the xylem vessel and relative expression level of aquaporins (AQP) genes of node were observed in Z4 than RIL plants under drought stress compared with the corresponding control. Thereby, we deduced that the node act as a “node switch” to control panicle water status by mediating the hydraulic resistance through changing the xylem diameter and the expression level of AQP genes under drought stress.

TiO2 prices reach $3.50-3.60 per kilo, but will this turn out to be the ceiling?

The importance of rice resistance to abiotic stress has largely been attributed to signal-induced closure of stomata, protection of antioxidase enzymes, and osmotic adjustment of sugars, etc. However, regulation role of nodes in water flow under drought stress has not been reported. Two rice genotypes Z4 and its recombinant inbred line (RIL) were subjected to drought stress for 10 d at the pollen mother cell meiosis stage. Results indicated a higher decline in spikelet fertility was found in RIL than Z4 plants under drought stress compared with the corresponding control. However, the leaves of Z4 plants were wilting 1 d earlier than those of RIL plants under drought stress. Accordingly, a greater decline in the RWC and water potential of the leaf and sheath, but a lower decrease in the panicle, was observed in the Z4 plants than the RIL plants. In the process, higher decrease in transpiration rate of leaf, hydraulic conductance, diameter of the xylem vessel and relative expression level of aquaporins (AQP) genes of node were observed in Z4 than RIL plants under drought stress compared with the corresponding control. Thereby, we deduced that the node act as a “node switch” to control panicle water status by mediating the hydraulic resistance through changing the xylem diameter and the expression level of AQP genes under drought stress.

Adaptation of the Pivotal-Differential Genome Pattern for the Induction of Intergenomic Chromosome Recombination in Hybrids of Synthetic Amphidiploids within Triticeae Tribe.

A pivotal-differential evolution pattern is when two allopolyploids share a common genome, which is called pivotal, and differ with respect to the other genome or genomes, called differential. This feature induces the intergenomic recombination between chromosomes of differential genomes, which can lead to speciation. Our study is a cytomolecular insight into this mechanism which was adapted for the induction of intergenomic chromosome recombination in hybrids of synthetic amphidiploids Aegilops biuncialis × S. cereale (UUMMRR) and triticale (AABBRR) where R-genome was pivotal. We observed chromosome recombination events which were induced by both: (1) random chromosome fragmentation and non-homologous chromosome end joining at mitosis of root meristem cells and (2) intergenomic chromosome associations at meiosis of pollen mother cells (PMCs) of F1 hybrids. Reciprocal chromosome translocations were identified in six F1 plants and 15 plants of F2 generation using fluorescence in situ hybridization (FISH) with DNA clones (pTa-86, pTa-k374, pTa-465, pTa-535, pTa-k566, and pTa-713). We observed signals of pTa-86, pTa-535, and pTa-k566 probes in several chromosome breakpoints. The comparison of the DNA clone sequences distinguished a number of common motifs, which can be considered as characteristics of chromosome breakpoint loci. Immunodetection of synaptonemal complex proteins and genomic in situ hybridization analysis at meiosis of PMCs of F1 hybrids showed, that the homologous pairing of pivotal R—genome chromosomes is crucial for the fertility of F1 hybrids, however, these chromosomes can be also involved in the intergeneric recombination.

Sugars, antioxidant enzymes and IAA mediate salicylic acid to prevent rice spikelet degeneration caused by heat stress

Salicylic acid (SA) can alleviate damage to rice plants induced by heat stress, but its role in preventing spikelet degeneration under high-temperature stress has not been documented. Rice plants pretreated with SA (0–50 mmol L−1) were subjected to heat stress at 40 °C at the pollen mother cell meiosis stage for 10 days. The results indicated that there were no significant differences in grain yields and yield components among rice plants that were exogenously sprayed with SA (0–50 mmol L−1) under natural conditions. Under heat stress, the grain yield, spikelet number per panicle and setting rate in response to SA treatments were higher than under the control (0 mmol L−1 SA or NON-SA) treatment, especially with 1 and 10 mmol L−1 SA. A higher grain yield, spikelet number per panicle and setting rate were recorded in these two SA treatments compared with the NON-SA treatment. During this process, soluble sugars, proline, phytohormones including ABA, GA3, BRs, IAA, ZR and JA, and antioxidant enzymes, such as superoxide dismutase, peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX), were induced by SA. Moreover, soluble sugars, IAA, POD and APX in the spikelets with SA treatments were not only higher than with the NON-SA treatment but the changing patterns were also similar to that of the spikelet number per panicle under natural conditions and heat stress. Therefore, our results suggest that sugars, antioxidant enzymes and IAA might mediate SA to prevent spikelet degeneration caused by heat stress.

Timing of Reproductive Organs Maturity in Proterandrous Malva sylvestris L.

Flower development of protandrous species Malva sylvestris L. was divided into 12 stages, as revealed by applying histological and scanning electron microscope techniques. Flower development started with the conversion of apical meristem into floral meristem. Initiation of male organ primordia started before that of female organ. Five rounded structures called corolla/androecium units differentiated from floral meristem, on which stamen primordia emerged. When pollen mother cells exist in the pollen sacs, initiation of carpels starts from floral meristem. Concurrent with the termination of meiosis in pollen mother cells, ten loculed ovary comed in view. Simultaneously with the occurrence of vacuoleted pollen grains, megaspore mother cell becomes visible in the nucellar tissue. Concominant with the existence of two celled-pollen grains, the style was formed and ovule becomes anatropous. When pollen grains are shed in male phase, ten branched stigma appeared on the upper part of the style, but receptive surface was not fully formed to accept pollen grains. Female phase is characterized by the opening of stigmatic branches with papillate receptive surface. Timing of reproductive organs maturity overlapped for a while, thus, the reproductive stragey of M. sylvestris was incomplete proterandry.

Gametocidal Factor Transferred from Aegilops geniculata Roth Can Be Adapted for Large-Scale Chromosome Manipulations in Cereals.

Segregation distorters are curious, evolutionarily selfish genetic elements, which distort Mendelian segregation in their favor at the expense of others. Those agents include gametocidal factors (Gc), which ensure their preferential transmission by triggering damages in cells lacking them via chromosome break induction. Hence, we hypothesized that the gametocidal system can be adapted for chromosome manipulations between Triticum and Secale chromosomes in hexaploid triticale (×Triticosecale Wittmack). In this work we studied the little-known gametocidal action of a Gc factor located on Aegilops geniculata Roth chromosome 4Mg. Our results indicate that the initiation of the gametocidal action takes place at anaphase II of meiosis of pollen mother cells. Hence, we induced androgenesis at postmeiotic pollen divisions (via anther cultures) in monosomic 4Mg addition plants of hexaploid triticale (AABBRR) followed by production of doubled haploids, to maintain the chromosome aberrations caused by the gametocidal action. This approach enabled us to obtain a large number of plants with two copies of particular chromosome translocations, which were identified by the use of cytomolecular methods. We obtained 41 doubled haploid triticale lines and 17 of them carried chromosome aberrations that included plants with the following chromosome sets: 40T+Dt2RS+Dt2RL (5 lines), 40T+N2R (1), 38T+D4RS.4BL (3), 38T+D5BS-5BL.5RL (5), and 38T+D7RS.3AL (3). The results show that the application of the Gc mechanism in combination with production of doubled haploid lines provides a sufficiently large population of homozygous doubled haploid individuals with two identical copies of translocation chromosomes. In our opinion, this approach will be a valuable tool for the production of novel plant material, which could be used for gene tracking studies, genetic mapping, and finally to enhance the diversity of cereals.

Embryological studies on Spiranthes sinensis (Pers.) Ames

Spiranthes sinensis (Pers.) Ames is one of the two rare native terrestrial orchids in Taiwan. In this work, we aimed to characterize its reproductive development. The male gametophytes (pollen) mature earlier than the female gametophytes (embryo sacs). Meiosis of pollen mother cells begins 15–16days before anthesis and pollen develop into the bi-cellular stage 7–8days later. Pollen reach maturity at the time of anthesis, while the embryo sacs remain at the megaspore mother cell stage. The embryo sacs mature 5days after flower opens. The pattern of embryo sac development is of the Polygonum type. There are 5 nuclei in a mature embryo sac. Pollination can hasten embryo sac maturation by approximately 3 days, compared to a non-pollinated flower. In a successful fertilization event, pollen tubes enter the embryo sacs 2days after pollination and the zygotes form soon after. Globular embryos are evident on the 5th day post-pollination. There is no endosperm development in mature seeds. A developmental reproductive calendar is presented showing key reproductive events leading to embryo formation for future comparative studies.

Analysis of gemini pollen 3 mutant suggests a broad function of AUGMIN in microtubule organization during sexual reproduction in Arabidopsis.

In flowering plants, male gametes arise via meiosis of diploid pollen mother cells followed by two rounds of mitotic division. Haploid microspores undergo polar nuclear migration and asymmetric division at pollen mitosis I to segregate the male germline, followed by division of the germ cell to generate a pair of sperm cells. We previously reported two gemini pollen (gem) mutants that produced twin-celled pollen arising from polarity and cytokinesis defects at pollen mitosis I in Arabidopsis. Here, we report an independent mutant, gem3, with a similar division phenotype and severe genetic transmission defects through pollen. Cytological analyses revealed that gem3 disrupts cell division during male meiosis, at pollen mitosis I and during female gametophyte development. We show that gem3 is a hypomorphic allele (aug6-1) of AUGMIN subunit 6, encoding a conserved component in the augmin complex, which mediates microtubule (MT)-dependent MT nucleation in acentrosomal cells. We show that MT arrays are disturbed in gem3/aug6-1 during male meiosis and pollen mitosis I using fluorescent MT-markers. Our results demonstrate a broad role for the augmin complex in MT organization during sexual reproduction, and highlight gem3/aug6-1 mutants as a valuable tool for the investigation of augmin-dependent MT nucleation and dynamics in plant cells.

Phosphatidylinositol 4-phosphate 5-kinases 1 and 2 are involved in the regulation of vacuole morphology during Arabidopsis thaliana pollen development

The pollen grains arise after meiosis of pollen mother cells within the anthers. A series of complex structural changes follows, generating mature pollen grains capable of performing the double fertilization of the female megasporophyte. Several signaling molecules, including hormones and lipids, have been involved in the regulation and appropriate control of pollen development. Phosphatidylinositol 4-phophate 5-kinases (PIP5K), which catalyze the biosynthesis of the phosphoinositide PtdIns(4,5)P2, are important for tip polar growth of root hairs and pollen tubes, embryo development, vegetative plant growth, and responses to the environment. Here, we report a role of PIP5Ks during microgametogenesis. PIP5K1 and PIP5K2 are expressed during early stages of pollen development and their transcriptional activity respond to auxin in pollen grains. Early male gametophytic lethality to certain grade was observed in both pip5k1−/− and pip5k2−/− single mutants. The number of pip5k mutant alleles is directly related to the frequency of aborted pollen grains suggesting the two genes are involved in the same function. Indeed PIP5K1 and PIP5K2 are functionally redundant since homozygous double mutants did not render viable pollen grains. The loss of function of PIP5K1 and PIP5K2results in defects in vacuole morphology in pollen at the later stages and epidermal root cells. Our results show that PIP5K1, PIP5K2 and phosphoinositide signaling are important cues for early developmental stages and vacuole formation during microgametogenesis.

Transmission of the Aegilops ovata chromosomes carrying gametocidal factors in hexaploid triticale (×Triticosecale Wittm.) hybrids.

The main aim of this work was to induce the chromosome rearrangements between Aegilops ovata (UUMM) and hexaploid triticale (AABBRR) by expression of the gametocidal factor located on the chromosome 4M. The Aegilops ovata × Secale cereale (UUMMRR) amphiploids and triticale ‘Moreno’ were used to produce hybrids by reciprocal crosses. Chromosome dynamics was observed in subsequent generations of hybrids during mitotic metaphase of root meristems and first metaphase of meiosis of pollen mother cells. Chromosomes were identified by genomic in situ hybridisation (GISH) and fluorescence in situ hybridisation (FISH) using pTa71, pTa791, pSc119.2 and pAs1 DNA probes. It has been shown that the origin of the genetic background had an influence on Aegilops chromosome transmission. Moreover, it has been reported that the preferential transmission of chromosome 4M appeared during both androgenesis and gynogenesis. It is also hypothesised that the expression of the triticale Gc gene suppressor had an influence on the semi-fertility of hybrids but did not inhibit the chromosome rearrangements. This paper also describes the double haploid production, which enabled to obtain plants with two identical copies of triticale chromosomes with translocations of Aegilops chromatin segments.

Comparative microsporogenesis and flower development in Eucalyptus urophylla × E. grandis

Microsporogenesis and flower development in Eucalyptus urophylla × E. grandis were examined using chromosome tableting to provide a method to predict the meiotic stages in this species. Although microsporogenesis was normal, cytokinesis during meiosis of pollen mother cells occurred simultaneously, with strong asynchronism observed in the two different lengths of stamens in a flower bud. In a single flower, the developmental period of microsporogenesis in anthers on the longer stamens was always ahead of those on the shorter stamens. Flower development was also asynchronous at different locations on a branch. Flower buds on the upper side of the branch were larger in diameter than those on the lower side. In addition, a correlation was observed between microsporogenesis development and flower bud diameter growth. The pachytene stage was first observed when the diameter of the flower buds increased to 3.0 mm, and the majority of the meiotic stages were observed when bud diameters ranged from 3.5 to 5.0 mm. This study showed that the developmental stages of microsporogenesis in Eucalyptus urophylla × E. grandis could be distinguished readily, which may be applicable to future breeding studies.

Unreduced gamete formation in wheat: Aegilops triuncialis interspecific hybrids leads to spontaneous complete and partial amphiploids

Production of unreduced or 2n gametes during meiosis is a common consequence of interspecific hybridization in plants. In the present work, five different bread wheat cultivars were crossed with an accession of Ae. triuncialis and interspecific F1 hybrids (MVT, NAT, OMT, PIT and ZAT) were produced. Meiosis in pollen mother cells (PMCs) of F1 hybrids, pollen viabilities, and seed set ratio were analyzed. Restitution meiosis and consequently unreduced viable pollen were observed. Immunolabeling against phosphorylated histone H3 at serine-10 (phosphoH3S10) suggested that unreduced male gametes were produced by first division restitution (FDR). FDR was more frequent in some hybrids, resulting in higher rates of unreduced male gamete formation and F2 seed set. The F2 embryos were highly variable in chromosome number ranging from 35 to 70 suggesting that unreduced gamete formation led to spontaneous partial and complete amphiploids.

Allocation of the S-genome chromosomes of Aegilops variabilis Eig. carrying powdery mildew resistance in triticale (× Triticosecale Wittmack).

It has been hypothesized that the powdery mildew adult plant resistance (APR) controlled by the Pm13 gene in Aegilops longissima Schweinf. & Muschl. (SlSl) has been evolutionary transferred to Aegilops variabilis Eig. (UUSS). The molecular marker analysis and the visual evaluation of powdery mildew symptoms in Ae. variabilis and the Ae. variabilis × Secale cereale amphiploid forms (2n = 6x = 42, UUSSRR) showed the presence of product that corresponded to Pm13 marker and the lower infection level compared to susceptible model, respectively. This study also describes the transfer of Ae. variabilis Eig. (2n = 4x = 28, UvUvSvSv) chromosomes, carrying powdery mildew resistance, into triticale (× Triticosecale Wittm., 2n = 6x = 42, AABBRR) using Ae. variabilis × S. cereale amphiploid forms. The individual chromosomes of Ae. variabilis, triticale ‘Lamberto’ and hybrids were characterized by genomic and fluorescence in situ hybridization (GISH/FISH). The chromosome configurations of obtained hybrid forms were studied at first metaphase of meiosis of pollen mother cells (PMCs) using GISH. The statistical analysis showed that the way of S-genome chromosome pairing and transmission to subsequent hybrid generations was diploid-like and had no influence on chromosome pairing of triticale chromosomes. The cytogenetic study of hybrid forms were supported by the marker-assisted selection using Pm13 marker and visual evaluation of natural infection by Blumeria graminis, that allowed to select the addition or substitution lines of hybrids carrying chromosome 3Sv which were tolerant to the powdery mildew infection.