Sexual Plant Reproduction最新文献

Rubus subgen. Rubus includes common European species with highly complicated taxonomy, ongoing hybridisation and facultative apomixis. Out of approximately 750 species recognised in Europe, only 3 diploid sexual species are known, along with numerous apomictic brambles that are highly connected to polyploidy. One exception of a tetraploid taxon is R. ser. Glandulosi, which is known for prevalent sexuality. This taxon highly hybridises with tetraploid members of R. ser. Discolores and leads to the origin of many hybridogenous populations and individuals. In this study, we verify reproduction modes in different diploid, triploid and tetraploid species of subgen. Rubus, with focus on taxa putatively involved in such hybridisation by applying flow cytometric seed screen analysis. We found 100 % sexuality of diploid species, whereas triploid species had obligate unreduced embryo sac development. In contrast, tetraploid plants had varying degrees of sexuality. Additionally, we discovered that R. bifrons has the ability to undergo a reproduction mode switch as a reaction to environmental conditions. These results provide insight into reproductive modes of European brambles and shed light on their reticulate evolution and speciation.

Apogamy is a phenomenon in which a sporophyte develops asexually, directly from a cell or cells of a gametophyte. It is a phenomenon described mainly in lower plants, but shares certain aspects with apomixis in angiosperms. The genes involved in apogamy commitment in ferns are unknown. We hypothesize that the mechanism of asexual reproduction is controlled in lower and higher plants by overlapping sets of genes. To this end, we created a normalized subtracted cDNA library that represents genes with increased expression during apogamy commitment in the fern Ceratopteris richardii. The cDNA library consists of 170 unique sequences. Compared to the mature gametophyte transcriptome of the fern Pteridium aquilinum, the apogamy library is enriched in plant GO-Slim terms that are associated with stress and metabolism. In silico expression analyses of the closest Arabidopsis homologs of the apogamy library revealed many genes that display preferential expression in seed and flower tissues, structures that are absent in ferns. This apogamy library provides a rich resource for investigations into the genetic control of apogamy in ferns and comparisons with the asexual processes of higher plants.

The Lilium longiflorum gH2A promoter is active exclusively in the generative cells of mature pollen in transgenic tobacco expressing the gH2A promoter::GUS (β-glucuronidase) construct as a reporter gene. Temporal and spatial aspects of gH2A promoter activity examined during pollen development in transgenic tobacco reveal that GUS reporter activity was not detected until developing pollen entered the early bicellular developmental stage. Activity was first detected in generative cells at early-mid stages and gradually increased to maximum levels at mid-bicellular stages. The patterns of appearance and longevity of GUS activity in tobacco were very similar to those of gH2A mRNA during pollen development in Lilium. Exogenous treatment with colchicine, a well-known microtubule depolymerize, blocked microspore mitosis and inhibited generative cell differentiation. No GUS signal was detected in the resulting anomalous pollen, which lacked generative cell differentiation. These data strongly suggest that normal generative cell development is essential for activation of the gH2A promoter. Furthermore, these results indicate that common transcriptional activator(s) of the gH2A promoter may be present in both Lilium and Nicotiana, and that such putative factor(s) activates the gH2A promoter only when generative cells undergo normal development.

Colchicine-induced neoautotetraploid genotypes of Acacia mangium were cloned and planted in mixture with a set of diploid clones in an orchard in southern Vietnam. Following good general flowering, open-pollinated seed was collected from trees of both cytotypes and microsatellite markers were used to determine the breeding system as characterised by the proportion of outcrosses in young seedling progeny. As predicted from the literature, the progeny of diploid clones were predominantly outcrossed (t(m) = 0.97). In contrast, the progeny of the tetraploid clones were almost entirely selfs (t(m) = 0.02; 3 of 161 seedlings assayed were tetraploid outcrosses and there were no triploids). Segregation at loci heterozygous in the tetraploid mothers followed expected ratios, indicating sexual reproduction rather than apomixis. Post-zygotic factors are primarily responsible for divergence of the breeding systems. Commonly, less than 1 % of Acacia flowers mature as a pod, and after mixed pollination, diploid outcrossed seed normally develops at the expense of selfs. Selfs of the tetraploid trees appear to express less genetic load and have a higher probability of maturing. However, this does not fully explain the observed deficiency of outcross tetraploid progeny. Presumably, there are cytogenetic reasons which remain to be investigated. In nature, selfing would increase the probability of establishment of neotetraploids irrespective of cytotype frequency in the population. Breeders need to review their open-pollinated breeding and seed production strategies. It remains to be seen whether this is an ephemeral problem, with strong fertility selection restoring potential for outcrossing over generations.

Seedlessness is an important economic trait of lemon. Understanding the cellular and molecular mechanisms of seedlessness in 'Xiangshui' lemon requires detailed data on pollen and embryo sac fertility, embryo development and compatibility mechanisms governing self- and cross-pollination. The results of the current study indicate that the fertility of pollen and mature embryo sac remains normal. When flowers were self- or cross-pollinated, pollen grains of 'Xiangshui' were able to germinate on the stigma. In the case of self-pollination, pollen tubes became twisted, tube tips enlarged and tubes ruptured in the bottom of stigma. Following cross-pollination, tubes were able to grow normally in the style and ovary and enter the embryo sac, where double fertilization took place. Embryonic development resulting from cross-pollination was normal. After cross-pollination, the zygote began to divide at 2 weeks post-pollination, with early globular embryos observed after 3 weeks, globular and heart-shaped embryos at 4 weeks, torpedo-shaped embryos at 5 weeks, cotyledonary embryos at 6 weeks and thereafter germinable seeds. After self-pollination, however, ovules began to abort at 2 weeks post-pollination, with ovules disappearing at 5 weeks, ultimately producing seedless fruits. Emasculated unpollinated flowers also developed into seedless fruits, indicating that seedlessness contributes to parthenocarpy. However, gametophytic self-incompatibility has a major role in seedlessness in 'Xiangshui' lemon by blocking fertilization at the bottom of the stigma.

Japanese pear has a genetically controlled self-incompatibility system, but both the pollen-tube growth in a semi in vivo assay and fruit set after self-pollination differ considerably among cultivars. The percentage of styles in which pollen tubes have reached the base ranges from 0 to 36 %, a value determined by culture of styles in vitro, and fruit set ranges from 0.6 to 15.2 %. Based on these data, we have assigned a value for the self-incompatibility weakness to each cultivar. Here, we showed that pollen factors control the degree of self-incompatibility. When the pollen-tube growth of 13 cultivars was compared in a completely compatible 'Hougetsu' (S (1) S (7)) style, it differed a fair amount among cultivars and showed a significantly positive relation to self-incompatibility weakness (r = 0.707). The degree of self-incompatibility of pear is, therefore, determined by pollen factor(s) unrelated to the S-locus. Although the fruit set and fruit growth of 'Hougetsu' were not affected by the pollen donor, a positive relationship was also observed between seed number and self-incompatibility weakness (r = 0.972). However, in a style with no S-RNase production (genotype: S (4) (sm) S (4) (sm) ), the relationship disappeared (r = 0.341) and pollen-tube growth was promoted by 12-36 % except in one cultivar. These results suggest that S-RNase functions as a cytotoxin on compatible pollen in a cultivar-dependent manner, and that the degree of inhibition is determined by pollen factor(s) unrelated to the S-locus. The pollen factor also functions on S-RNase in incompatible styles, resulting in a different degree of self-incompatibility.

The genus Limonium Miller, a complex taxonomic group, comprises annuals and perennials that can produce sexual and/or asexual seeds (apomixis). In this study, we used diverse cytogenetic and cytometric approaches to analyze male sporogenesis and gametogenesis for characterizing male reproductive output on seed production in Limonium ovalifolium and Limonium multiflorum. We showed here that the first species is mostly composed of diploid cytotypes with 2n = 16 chromosomes and the latter species by tetraploid cytotypes with 2n = 32, 34, 35, 36 chromosomes and had a genome roughly twice as big as the former one. In both species, euploid and aneuploid cytotypes with large metacentric chromosomes having decondensed interstitial sites were found within and among populations, possibly involved in chromosomal reconstructions. L. ovalifolium diploids showed regular meiosis resulting in normal tetrads, while diverse chromosome pairing and segregation irregularities leading to the formation of abnormal meiotic products are found in balanced and non-balanced L. multiflorum tetraploids. Before anther dehiscence, the characteristic unicellular, bicellular, or tricellular pollen grains showing the typical Limonium micro- or macro-reticulate exine ornamentation patterns were observed in L. ovalifolium using scanning electron microscopy. Most of these grains were viable and able to produce pollen tubes in vitro. In both balanced and unbalanced L. multiflorum tetraploids, microspores only developed until the "ring-vacuolate stage" with a collapsed morphology without the typical exine patterns, pointing to a sporophytic defect. These microspores were unviable and therefore never germinated in vitro. L. ovalifolium individuals presented larger pollen grains than those of L. multiflorum, indicating that pollen size and ploidy levels are not correlated in the Limonium system. Cytohistological studies in mature seeds from both species revealed that an embryo and a residual endosperm were present in each seed. Flow cytometric seed screens using such mature seeds showed quantitative variations in seeds ploidy level. It is concluded that male function seems to play an important role in the reproduction modes of Limonium diploids and tetraploids.

Iridaceae is one of the few families in which floral oils are produced and collected by pollinators as a resource. Perigonal nectaries and trichomal elaiophores are highly unusual within the tribe Sisyrinchieae. Both structures occur mainly on the staminal column, while they are usually distributed on the tepals in the other tribes of the subfamily Iridoideae. Sisyrinchieae is the largest tribe of Iridaceae present on the American continent, and the diversity observed may be related to the exceptional development of trichomal elaiophores within the genus Sisyrinchium, but knowledge concerning the other types of nuptial glandular structures within the tribe is still limited, preventing us from estimating their implication for species diversity. Structural observations and histochemical tests were performed to identify and characterize glandular structures and pollen rewards within the flowers of the genera Orthrosanthus, Sisyrinchium and Solenomelus. Perigonal nectaries were detected only in Solenomelus segethi, and trichomal elaiophores were characterized only within Sisyrinchium. All species showed large amounts of additional resources available for pollinators in the form of pollenkitt and polysaccharides present in the cytoplasm of the pollen grains. The results are discussed in a phylogenetic context, with regard to pollinators and floral rewards reported for the tribe Sisyrinchieae.

Siphonogamy is a critical process in plant reproductive growth, during which numerous cell-cell interaction events occur between pistil and pollen. Previous studies in Solanaceae, Papaveraceae, and Brassicaceae focusing on pollen-stigma recognition in self-incompatible systems have provided many important views. In this study, we profiled the proteome in soybean mature pistils before and after pollination. Comparative analyses of two-dimensional gel electrophoresis maps from un-pollinated and pollinated pistils were conducted. The results showed that 22 proteins were increased and 36 proteins decreased after pollination. Functional categorization showed that most of them were metabolism- and redox-related proteins. The enhancement of primary metabolism, biosynthesis of pollen tube guidance compounds, and adjustment of redox homeostasis system might be helpful for a successful pollination. Quantitative reverse transcript-polymerase chain reaction analysis implied that the regulation of gene expression might happen at both transcriptional and posttranscriptional levels during pollination. This study will enhance our understanding of pollen-stigma interaction in plant sexual reproductive growth.

Cocoa (Theobroma cacao) has an idiosyncratic form of late-acting self-incompatibility that operates through the non-fusion of incompatible gametes. Here, we used high-resolution confocal microscopy to define fine level changes to the embryo sac of the strongly self-incompatible cocoa genotype SCA 24 in the absence of pollination, and following compatible and incompatible pollination. All sperm nuclei had fused with the female nuclei by 48 h following compatible pollinations. However, following incompatible pollinations, we observed divergence in the behaviour of sperm nuclei following release into the embryo sac. Incomplete sperm nucleus migration occurred in approximately half of the embryo sacs, where the sperm nuclei had so far failed to reach the female gamete nuclei. Sperm nuclei reached but did not fuse with the female gamete nuclei in the residual cases. We argue that the cellular mechanisms governing sperm nucleus migration to the egg nucleus and those controlling subsequent nuclear fusion are likely to differ and should be considered independently. Accordingly, we recommend that future efforts to characterise the genetic basis of LSI in cocoa should take care to differentiate between these two events, both of which contribute to failed karyogamy. Implications of these results for continuing efforts to gain better understanding of the genetic control of LSI in cocoa are discussed.