Characteristics of the cytomixis in the pollen mother cells of transgenic tobacco plants (Nicotiana tabacum L.) with mutant phenotype

This paper represents the frequency characteristics and cytological analysis of cytomixis in the course of male meiosis in transgenic tobacco plants (Nicotiana tabacum L.) with altered flower morphology and male sterility. The influence of cytomixis on qualitative composition of the meiotic products is shoron (cytoplasts and polyads formation). It was established that doubling of chromosomes number increased cytomixis frequency in the investigated plants.     

Peculiarities of cytomixis in pollen mother cells of transgenic tobacco plants (Nicotiana tabacum L.) with mutant phenotype

The frequency characteristics and cytological picture of cytomixis in the course of male meiosis are described in transgenic tobacco plants (Nicotiana tabacum L.) with altered flower morphology and male sterility. Effects of cytomixis on qualitative composition of meiotic products are studied (formation of cytoplasts and polyads). Doubling of the chromosome number was established to increase frequency of cytomixis in the studied plants.     

植物细胞核雄性不育相关bHLH转录因子研究进展

雄性不育广泛存在于种子植物中。植物雄性不育不仅是植物生殖发育研究的重要内容,同时也可作为杂种优势利用的有效工具,因而具有重要的理论和应用价值。bHLH转录因子家族是植物中成员最多的转录因子家族,在植株的整个生长发育过程中起着重要的调控作用。本文介绍了拟南芥、水稻、玉米等几种重要模式植物bHLH转录因子调控雄蕊发育的作用机制,并重点阐述其功能异常引起细胞核雄性不育的分子机制,以期为作物育种与理论研究提供参考。     

First detection of cytomixis and its consequences in <Emphasis Type="Italic">Thalictrum cultratum</Emphasis> Wall. (Ranunculaceae)

In current paper, we studied the meiotic chromosome number and details of cytomixis recorded for the first time in Thalictrum cultratum Wall. from the high altitude areas of northwest Himalaya (India). Cytomixis, the phenomenon of inter PMC (pollen mother cell) migration of chromatin material has been reported in many angiosperms and other groups of plants, but there is no published report in Thalictrum cultratum. All the presently studied accessions of the species existed at diploid level (x = 7). The present chromosome count of n = 14 has been reported for the first time from the study area. The cytological stability of any plant is an important consideration in view of its existence in nature. Meiotic disturbances can impose threat to the reproductive potential of plant. Current study reveals the occurrence of inter PMC migration of chromatin material. In present investigation, the phenomenon of cytomixis can be observed between 2 to 9 PMCs. Chromatin migration occurs through narrow and broad cytoplasmic channels or occasionally fused together during metaphase-I and anaphase-I. Cytomixis resulted in the formation of hypo- (n = 2, 2 + 1 small fragment, n = 3 + 3 small fragments, 4, 5 + extra mass of chromatin, 13) and hyperploid (n = 7 + 2 small fragments, 8 + 2 small fragments, 14, 14 + 2 small fragments, 15) PMCs, variable sized pollen grains and pollen sterility (20%). The current study reveals that cytomixis is responsible for formation of PMCs with variable chromosomes (hypoand hyperploid) and pollen grains of heterogeneous sizes and pollen sterility in T. cultratum. This is the first report of cytomixis in the species.     

The pachytene checkpoint and its relationship to evolutionary patterns of polyploidization and hybrid sterility

Sterility is a commonly observed phenotype in interspecific hybrids. Sterility may result from chromosomal or genic incompatibilities, and much progress has been made toward understanding the genetic basis of hybrid sterility in various taxa. The underlying mechanisms causing hybrid sterility, however, are less well known. The pachytene checkpoint is a meiotic surveillance system that many organisms use to detect aberrant meiotic products, in order to prevent the production of defective gametes. We suggest that activation of the pachytene checkpoint may be an important mechanism contributing to two types of hybrid sterility. First, the pachytene checkpoint may form the mechanistic basis of some gene-based hybrid sterility phenotypes. Second, the pachytene checkpoint may be an important mechanism that mediates chromosomal-based hybrid sterility phenotypes involving gametes with non-haploid (either non-reduced or aneuploid) chromosome sets. Studies in several species suggest that the strength of the pachytene checkpoint is sexually dimorphic, observations that warrant future investigation into whether such variation may contribute to differences in patterns of sterility between male and female interspecific hybrids. In addition, plants seem to lack the pachytene checkpoint, which correlates with increased production of unreduced gametes and a higher incidence of polyploid species in plants versus animals. Although the pachytene checkpoint occurs in many animals and in fungi, at least some of the genes that execute the pachytene checkpoint are different among organisms. This finding suggests that the penetrance of the pachytene checkpoint, and even its presence or absence can evolve rapidly. The surprising degree of evolutionary flexibility in this meiotic surveillance system may contribute to the observed variation in patterns of hybrid sterility and in rates of polyploidization.     

Patterns of male sterility within and among populations of the distylous shrub Erythroxylum havanense (erythroxylaceae)

Distyly, a reproductive system characterized by the presence of long-styled (thrum). and short-styled (pin) individuals within a population, has been repeatedly used as a model for the study of the evolution of the reproductive systems in plants. Erythroxylum havanense is a distylous species in which most thrum plants fail to develop a fertile androecium, thus behaving as male-sterile or partially male-sterile plants. Short-styled (thrum) individuals have an increased performance as female parents, thereby compensating for their loss of male fitness. Previous studies of populations within close proximity to each other suggest that E. havanense may be involved in a process of gender specialization in which, unlike other heterostylous species, thrum plants are specializing as females and pins (long-styled) as males. In this paper we describe more general patterns of male sterility, one of the first steps in the evolution of gender specialization, among populations of the distylous shrub Erythroxylum havanense. Pollen germination differed among populations (range 0.52 ± 0.03 to 0.06 ± 0.04), and between morphs. Pollen from pin plants was almost two times (1.89) as fertile as that from thrums (0.36 ± 0.03 and 0.19 ± 0.03, pin and thrums respectively). Thrums were significantly more male sterile in four out of five populations. The population where differences between the floral morphs were not apparent showed the lowest levels of pollen fertility. Accordingly, our results indicate that populations of E. havanense show marked differences in pollen fertility and higher male sterility associated with the thrum morph. We hypothesize that differences between morphs could be explained if restorers of male sterility are linked to the distyly haplotype, while differences in genes associated with male sterility could explain the variation among populations. Overall, the prevalence of thrum-biased male sterility across populations suggests that E. havanense is subject to a process of gender specialization.     

Fractionated irradiation improves the mating performance of the West Indian sweet potato weevil Euscepes postfasciatus

• 1 The sterile insect technique (SIT) is widely used to suppress or eradicate target pest insect populations.
• 2 The effectiveness of SIT depends on the ability of released sterile males to mate with and inseminate wild females. The use of gamma radiation to induce sterility, however, negatively affects both somatic cells as well as reproductive cells. Consequently, mating performance of sterilized individuals decreases drastically over time. The mating propensity of sterilized Euscepes postfasciatus (Fairmaire) males irradiated with a single dose of 150 Gy (the current standard of the Okinawa Prefecture SIT programme) is equal to that of non‐irradiated weevils for the first 6 days.
• 3 Fractionated irradiation, in which a sterilizing dose is delivered over time in a series of smaller irradiations, reduces the damage of irradiation in insects. In the present study, we evaluated the effect of fractionated irradiation on male fertilization ability, longevity and mating propensity of E. postfasciatus for a period of 16 days after irradiation.
• 4 Although fractionated irradiation totalling 150 Gy was found to induce full sterility regardless of the number of individual doses, the mating propensity of male weevils sterilized by fractionated irradiation was maintained for the first 12 days. These results demonstrate that fractionated irradiation can be highly advantageous in programmes aimed at eradication of E. postfasciatus.

     

High-temperature stress in crops: male sterility,yield loss and potential remedy approaches

Global food security is one of the utmost essential challenges in the 21st century in providing enough food for the growing population while coping with the already stressed environment. High temperature (HT) is one of the main factors affecting plant growth, development and reproduction and causes male sterility in plants. In male reproductive tissues, metabolic changes induced by HT involve carbohydrates, lipids, hormones, epigenetics and reactive oxygen species, leading to male sterility and ultimately reducing yield. Understanding the mechanism and genes involved in these pathways during the HT stress response will provide a new path to improve crops by using molecular breeding and biotechnological approaches. Moreover, this review provides insight into male sterility and integrates this with suggested strategies to enhance crop tolerance under HT stress conditions at the reproductive stage.     

Effects of water stress on male gametophyte development in plants

 Male reproductive development in plants is highly sensitive to water deficit during meiosis in the microspore mother cells. Water deficit during this stage inhibits further development of microspores or pollen grains, causing male sterility. Female fertility, in contrast, is quite immune to stress. The injury is apparently not caused by desiccation of the reproductive tissue, but is an indirect consequence of water deficit in the vegetative organs, such as leaves. The mechanism underlying this stress response probably involves a long-distance signaling molecule, originating in the organs that undergo water loss, and affecting fertility in the reproductive tissue, which conserves its water status. Much research has been focused on the involvement of abscisic acid in this regard, but the most recent evidence tends to reject a role for this hormone in the induction of male sterility. Stress-induced arrest of male gametophyte development is preceded by disturbances in carbohydrate metabolism and distribution within anthers, and an inhibition of the key sugar-cleaving enzyme, acid invertase. Since invertase gene expression can be modulated by sugar concentration, it is possible that decreased sugar delivery to reproductive tissue upon inhibition of photosynthesis by stress is the signal that triggers metabolic lesions leading to failure of male gametophyte development. Received: 31 October 1996 / Revision accepted: 18 February 1997     

Environmentally induced variation in fecundity compensation in the morph-biased male-sterile distylous shrub Erythroxylum havanense (Erythroxylaceae)

The evolution of male-sterile individuals in hermaphroditic species represents the first step in the evolution of sex specialization. For male-sterile individuals to persist they must have some fitness advantage that compensates for their loss of the male function. Female fecundity also depends on environmental factors as those determining the likelihood of pollination and fertilization. Here we assessed the effects of both male sterility and reproductive synchrony (an environmentally affected trait) on the magnitude of female compensation of Erythroxylum havanense, a distylous shrub with morph-biased male sterility. In vitro measurements of pollen germination showed that thrums were more male sterile than pins. The compensatory advantage of thrums changed by a factor of five depending on flowering synchrony. Flowering in synchrony with the population increased fruit production in both morphs. However, because pins that flowered out of synchrony produced almost no fruits, the reproductive compensation of thrums was higher in these circumstances. Because the magnitude of compensation is frequently considered as a key factor in the evolution of sex specialization, the environmentally induced variation in the magnitude of the reproductive compensation of thrum plants may have profound effects on the evolutionary dynamics of the reproductive system of E. havanense.     

高通量转录组测序技术在植物雄性不育研究中的应用

植物雄性不育是指植物雄蕊发育受阻不能产生正常有功能花粉的现象。植物雄性不育不仅是生殖生理研究的宝贵材料,也是植物杂种优势利用的重要工具。由于高通量转录组测序技术几乎可以检测细胞内所有mRNA及非编码RNA的信息,已被广泛应用于生命科学研究的各项领域。在植物雄性不育相关研究中,高通量转录组测序技术在不同物种、不同败育类型中的应用已有报道,这为研究者在转录组水平综合了解植物雄性不育的分子机制及代谢网络提供了帮助。本文从测序文库构建策略、差异表达基因、非编码RNA的功能特征等方面综述了高通量转录组测序在植物雄性不育机理方面的研究进展,并探讨了转录组测序技术在花粉败育机制解析及育性相关基因定位中的应用价值,以期为植物雄性不育的相关研究提供参考。     

Speciation genes in plants

Background

Analyses of speciation genes – genes that contribute to the cessation of gene flow between populations – can offer clues regarding the ecological settings, evolutionary forces and molecular mechanisms that drive the divergence of populations and species. This review discusses the identities and attributes of genes that contribute to reproductive isolation (RI) in plants, compares them with animal speciation genes and investigates what these genes can tell us about speciation.

Scope

Forty-one candidate speciation genes were identified in the plant literature. Of these, seven contributed to pre-pollination RI, one to post-pollination, prezygotic RI, eight to hybrid inviability, and 25 to hybrid sterility. Genes, gene families and genetic pathways that were frequently found to underlie the evolution of RI in different plant groups include the anthocyanin pathway and its regulators (pollinator isolation), S RNase-SI genes (unilateral incompatibility), disease resistance genes (hybrid necrosis), chimeric mitochondrial genes (cytoplasmic male sterility), and pentatricopeptide repeat family genes (cytoplasmic male sterility).

Conclusions

The most surprising conclusion from this review is that identities of genes underlying both prezygotic and postzygotic RI are often predictable in a broad sense from the phenotype of the reproductive barrier. Regulatory changes (both cis and trans) dominate the evolution of pre-pollination RI in plants, whereas a mix of regulatory mutations and changes in protein-coding genes underlie intrinsic postzygotic barriers. Also, loss-of-function mutations and copy number variation frequently contribute to RI. Although direct evidence of positive selection on speciation genes is surprisingly scarce in plants, analyses of gene family evolution, along with theoretical considerations, imply an important role for diversifying selection and genetic conflict in the evolution of RI. Unlike in animals, however, most candidate speciation genes in plants exhibit intraspecific polymorphism, consistent with an important role for stochastic forces and/or balancing selection in development of RI in plants.Key words: Speciation, reproductive isolation, mating system isolation, pollinator isolation, ecological isolation, unilateral incompatibility, hybrid necrosis, hybrid sterility, hybrid inviability, hybrid breakdown, cytoplasmic male sterility, restoration     

Ecological and genetic factors contributing to the low frequency of male sterility in Chamaecrista Fasciculata (Fabaceae)

Bumble bee pollinated Chamaecrista fasciculata provides pollen as the sole reward to its pollinators. Male sterility, expressed as an absence or nearly complete absence of pollen production, occurs in low frequency in populations of C. fasciculata. Here we describe experiments, using C. fasciculata, to examine frequently cited determinants of the spread and maintenance of male sterility: compensation and the genetic basis of male sterility. In addition, we examine the role the pollination system plays in determining the reproductive success of the male steriles. Seventeen populations in Maryland, Illinois, and Kansas were surveyed and found to range from 0 to 6% male sterility per population. An artificial population of male-sterile simulants and hermaphrodites was created to examine how the local frequency of nonrewarding male steriles might affect male-sterile female reproductive success. Male steriles performed equally poorly, with respect to seed production, whether surrounded by other male-sterile simulants or hermaphrodites. Compensation was examined by comparison of male steriles and hermaphrodites with respect to several reproductive and nonreproductive characters. Male steriles outperformed hermaphrodites in terms of nonreproductive biomass, but performed equally in terms of ovule number and produced many fewer flowers. The genetic basis of male sterility was examined by performing both intra- and interpopulational crosses of male steriles to hermaphrodites and indicate that male sterility is not purely cytoplasmic. The low frequency of male sterility in C. fasciculata populations may reflect reduced female reproductive success because of pollinator avoidance, lack of reproductive compensation, and a mode of inheritance that is not purely cytoplasmic.     

Cellular and tissue mechanisms of recovery processes in Hordeum distichum L. under irradiation

Ionizing and UV-B irradiation of barley seedlings increased the number of chromosome aberrations in vegetative and generative meristems and disturbances in microsporo- and microgametogenesis. Other irradiation-induced changes included enhanced cytomixis and an increase in the number of pathologies in meiosis and tetrads and in the polymorphism and disturbances in pollen grains. Damages induced by different irradiation types differ primarily quantitatively. The dynamics of occurrence of chromosome aberrations in the root meristem reciprocally depended on the irradiation dose. Damages induced by low UV doses were detected throughout the ontogeny of plants. Increased irradiation doses activated cytolytic processes during premeiotic interphase, meiosis, and tetrad formation, as well as after the end of gametogenesis. Exposure to maximum doses of UV radiation and moderate doses of γ-radiation restored the fertility of grain pollens. Microsporocytes, microspores, and pollen grain components undergo degeneration primarily via apoptosis. This type of cell death is apparently autonomous, being induced by the cell population itself. The results of this study confirmed the hypothesis on the positive role of cell competition in the recovery processes and adaptation of plants to mutagens.     

Influence of UV-B radiation on the reproductive function of Hordeum vulgare L. plants

Irradiation of barley seedlings by ultraviolet-B radiation influences the growth and development of the sexual elements of the spike, accelerating differentiation of the sporogenous tissue of the anther and the male gametophyte, a phenomenon which is accompanied by an increase in the asynchronicity of microgametogenesis and in heterogeny of the pollen grains, and in an increase in the sterility of the pollen grains. High ultraviolet doses tend to reduce the level of sterility of the anther due to intensification of haplontic cell selection. The influence of ultraviolet irradiation on the reproductive system of the plant is expressed in genotoxic (through damage to the DNA of meristemic cells) and photo-inductive (through acceleration of efflorescence and differentiation of gametophytes) effects.     

Induced cytomictic variations and syncyte formation during microsporogenesis in <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> L.

The intercellular translocation of chromatin material along with other cytoplasmic contents among the proximate meiocytes lying in close contact with each other commonly referred as cytomixis was reported during microsporogenesis in Phaseolus vulgaris L., a member of the family Fabaceae. The phenomenon of cytomixis was observed at three administered doses of gamma rays viz. 100, 200, and 300 Gy respectively in the diploid plants of Phaseolus vulgaris L. The gamma rays irradiated plants showed the characteristic feature of inter-meiocyte chromatin/chromosomes transmigration through various means such as channel formation, beak formation or by direct adhesion between the PMC’s (Pollen mother cells). The present study also reports the first instance of syncyte formation induced via cytomictic transmigration in Phaseolus vulgaris L. Though the frequency of syncyte formation was rather low yet these could play a significant role in plant evolution. It is speculated that syncyte enhances the ploidy level of plants by forming 2n gametes and may lead to the production of polyploid plants. The phenomenon of cytomixis shows a gradual inclination along with the increasing treatment doses of gamma rays. The preponderance of cytomixis was more frequent during meiosis I as compared to meiosis II. An interesting feature noticed during the present study was the channel formation among the microspores and fusion among the tetrads due to cell wall dissolution. The impact of this phenomenon is also visible on the development of post-meiotic products. The formation of heterosized pollen grains; a deviation from the normal pollen grains has also been reported. The production of gametes with unbalanced chromosomes is of utmost importance and should be given more attention in future studies as they possess the capability of inducing variations at the genomic level and can be further utilized in the improvement of germplasm.     

被子植物有性生殖过程中的细胞程序死亡

细胞程序死亡是植物发育过程中的一种普遍现象。早就认识到高等植物生殖器官中一些细胞的死亡对植物有性生殖具有重要作用。这些细胞的死亡过程与动物组织中的细胞程序死亡基本相同。但植物体内诱导生殖细胞程序死亡的信号及其传导系统则显示出其特点 ,有些还表现出雌、雄性细胞的相互作用。探索植物生殖过程中的细胞程序死亡现象将有利于澄清植物生殖过程中的一些机理问题 ,使过去的细胞学研究结果深入到分子水平进行探讨     

Cytomixis in pollen mother cells of Medicago sativa L

Cytomixis (i.e., chromatin migration between meiocytes) has been detected in many plant species, but not in Medicago sativa spp. In the present study we report the identification of a few cytomictic alfalfa plants. Those plants, the "mother plants," were selfed and crossed with a normal control plant. Microsporogenesis analysis was performed on the mother plants, on the S(1) and F(1) plants, and on controls. The S(1) and F(1) plants, like the mother plants, were found to be cytomictic. Single or multiple chromatin bridges between two or more meiocytes were observed almost exclusively in prophase I. Some completely empty meiocytes were also observed. In addition to cytomixis, other meiotic abnormalities were found. Control plants showed an almost regular meiosis. The highest values of cytomixis were observed in the mother plants, and the lowest in their F(1) progenies. Variability of cytomixis in the F(1) plants is probably due to a heterozygotic condition of the parents for this trait. No significant correlation was found between cytomixis and pollen viability, even if the cytomictic plants showed low values of pollen viability.     

Male sterility in triploid dandelions: asexual females vs. asexual hermaphrodites

Male reproductive output, pollen in plants and sperm in animals has been shown to constitute a substantial cost for many organisms. In parthenogenetic hermaphrodites, selection is therefore expected to reduce the allocation of resources to male reproductive output. However, sustained production of pollen or sperm has been observed in numerous asexual hermaphrodites. We studied the widespread production of pollen by triploid asexual dandelions, Taraxacum sect. Ruderalia, comparing rare male sterile individuals with pollen producing asexuals. We found that individuals can show plasticity in the production of pollen, but that it is nevertheless possible to distinguish between (facultatively) male sterile asexuals and male fertile asexuals. Based on evidence from genetic markers and crosses, we conclude that the male sterility in asexual dandelions is caused by nuclear genes, in contrast to the cytoplasmically inherited male sterility previously found in sexual dandelions. Male sterile lineages did not produce more seeds per flower head, heavier seeds or seeds that were more viable. However, male sterile plants did produce more seed heads and hence more seeds than pollen producing ones, indicating that they were able to reallocate resources toward seed production. Considering the difference in seed production, it remains puzzling that not more asexual dandelions are male sterile.