Male Gametophyte Formation Research Articles

Male gametogenesis in flowering plants

The life cycles of plants are characterized by significant alternations between the diploid sporophytic and the haploid gametophytic generations. Meiosis and fertilization are the prerequisites for achieving the alternation of generations. Diploid sporophytes undergo meiosis to produce haploid gametes, and male–female gametes fuse (double fertilization) to revert to the diploid sporophyte. The formation and development of male gametophytes are crucial for the alternation of generations in higher plants. During the long evolution of plants from aquatic to terrestrial, the way of sexual reproduction has undergone subversive innovations. From sperm swimming for fertilization to relying on the precise delivery of pollen tubes to female gametes for the fusion of the male–female gametes, higher requirements are placed on the male gametophytes’ development and fertilization process. The formation of male gametophytes has undergone significant changes to meet the needs for delivery and transportation of the male gametes. With the emergence of more and more evidence, the molecular mechanism underlying male gametophytes’ development, especially the initiation and specialization of germline cells has been better understood. Focusing on the latest studies, we reviewed and elucidated the critical proteins and factors involved in male gametophyte formation, highlighting the decisive role of auxin in archesporial cell specialization and the importance of microspore maturation in pre-mitosis, and analyzed the molecular mechanisms underlying male gametogenesis, with a view to providing insights for further exploration of male gametophytes formation in the future.

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

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

Male meiosis in sweet cherry is constrained by the chilling and forcing phases of dormancy.

Male meiosis in temperate fruit trees occurs in the anthers once a year, synchronized with the seasons. The alternation of dormant and growth cycles determines the optimum moment for the male gametophyte formation, a process sensitive to both cold and warm temperatures. This ensures pollen viability and subsequent reproduction success that guarantee fruit production. In this work, we explore how male meiosis is framed by seasonality in sweet cherry. For this purpose, the dormant phases, male meiosis and blooming dates were established in four cultivars with different flowering dates and chilling requirements over 7 years. The chilling and heat requirements for each cultivar were empirically estimated, and chilling and heat temperatures were quantified according to the Dynamic and Growing Degree Hours (GDH) models, respectively. Endodormancy was overcome approximately a fortnight earlier during the colder winters than during the milder winters. Against our initial hypothesis, these differences were not clearly reflected in the time of male meiosis. The period between chilling fulfillment and meiosis lasted several weeks, during which a high amount of GDH accumulated. Results showed that male meiosis is conditioned by endodormancy but especially by warm temperatures, during the forcing period. This differs from what has been described in other related species and creates a framework for further studies to understand the strategies of synchronizing dormancy with seasons.

Morphological Features of the Anther Development in Tomato Plants with Non-Specific Male Sterility.

The study was devoted to morphological and cytoembryological analysis of disorders in the anther and pollen development of transgenic tomato plants with a normal and abnormal phenotype, which is characterized by the impaired development of generative organs. Various abnormalities in the structural organization of anthers and microspores were revealed. Such abnormalities in microspores lead to the blocking of asymmetric cell division and, accordingly, the male gametophyte formation. Some of the non-degenerated microspores accumulate a large number of storage inclusions, forming sterile mononuclear pseudo-pollen, which is similar in size and appearance to fertile pollen grain (looks like pollen grain). It was discussed that the growth of tapetal cells in abnormal anthers by increasing the size and ploidy level of nuclei contributes to this process. It has been shown that in transgenic plants with a normal phenotype, individual disturbances are also observed in the development of both male and female gametophytes. The reason for the developmental arrest of some ovules was the death of endosperm at different stages of the globular embryo. At the same time, noticeable hypertrophy of endothelial cells performing a secretory function was observed. In the ovules of transgenic plants with abnormalities, the endothelium forms a pseudo-embryo instead of the embryo sac, stimulating the development of parthenocarpic fruits. The data obtained in this study can be useful for a better understanding of the genetic and molecular mechanisms of cytoplasmic male sterility and parthenocarpic fruit development in tomatoes.

Distribution of plastids and mitochondria during male gametophyte formation in Tinantia erecta (Jacq.) Fenzl

During meiosis in microsporogenesis, autonomous cellular organelles, i.e., plastids and mitochondria, move and separate into daughter cells according to a specific pattern. This process called chondriokinesis is characteristic for a given plant species. The key criterion for classification of the chondriokinesis types was the arrangement of cell organelles during two meiosis phases: metaphase I and telophase I. The autonomous organelles participate in cytoplasmic inheritance; therefore, their precise distribution to daughter cells determines formation of identical viable microspores. In this study, the course of chondriokinesis during the development of the male gametophyte in Tinantia erecta was analyzed. The study was conducted using optical and transmission electron microscopes. During microsporogenesis in T. erecta, autonomous cell organelles moved in a manner defined as a neutral-equatorial type of chondriokinesis. Therefore, metaphase I plastids and mitochondria were evenly dispersed around the metaphase plate and formed an equatorial plate between the daughter nuclei in early telophase I. Changes in the ultrastructure of plastids and mitochondria during pollen microsporogenesis were also observed.

Abnormal development of floral meristem triggers defective morphogenesis of generative system in transgenic tomatoes.

Parthenocarpy and fruit malformations are common among independent transgenic tomato lines, expressing genes encoding different pathogenesis-related (PR) protein and antimicrobal peptides. Abnormal phenotype developed independently of the expression and type of target genes, but distinctive features during flower and fruit development were detected in each transgenic line. We analyzed the morphology, anatomy, and cytoembryology of abnormal flowers and fruits from these transgenic tomato lines and compared them with flowers and fruits of wild tomatoes, line YaLF used for transformation, and transgenic plants with normal phenotype. We confirmed that the main cause of abnormal flower and fruit development was the alterations of determinate growth of generative meristem. These alterations triggered different types of anomalous growth, affecting the number of growing ectopic shoots and formation of new flowers. Investigation of the ovule ontogenesis did not show anomalies in embryo sac development, but fertilization did not occur and embryo sac degenerated. Nevertheless, the ovule continued to differentiate due to proliferation of endothelium cells. The latter substituted embryo sac and formed pseudoembryonic tissue. This process imitated embryogenesis and stimulated ovary growth, leading to the development of parthenocarpic fruit. We demonstrated that failed fertilization occurred due to defective male gametophyte formation, which was manifested in blocked division of the nucleus in the microspore and arrest of vegetative and generative cell formation. Maturing pollen grains were overgrown microspores, not competent for fertilization but capable to induce proliferation of endothelium and development of parthenocarpic ovary. Thus, our study provided new data on the structural transformations of reproductive organs during development of parthenocarpic fruits in transgenic tomato.

Formation of a unique structure during microsporogenesis in Tinantia anomala (Commelinaceae) anthers

The analysis of microsporogenesis in Tinantia anomala revealed a unique ring-shaped structure assembling pollen grains into large aggregates. The heterogeneous ring was composed of several segments and was dominated by lipid compounds. Although the ring is a product of the tapetum, such a structure has not been described yet. The authors put forward some hypotheses for elucidation of the role of this structure in the process of male gametophyte formation.

Primary Study on Antheridiogen System of Dryopteris uniformis

This paper mainly studies the antheridiogen system of Dryopteris uniformis,which affecting the spore germination and gametophyte development of D.uniformis and Ceratopteris thalictroides.The result shows that; the gametophytes of D.uniformis can form antheridiogen,which could restrain the spore germination percentage of its own species.The restraining action of antheridiogen to the spore germination becomes stronger as the gametophyte grows more mature.Antheridiogen of D.uniformis can promote male gametophyte formation of itself. In the light,the antheridiogen of D.uniformis have no obvious influence on spore germination and gametophyte promotes C.thalictroides.However,in the dark situation,the antheridiogen of D.uniformis promotes spores to germinate much earlier.However,it does not make any influence on its ultimate germination percentage and sex differentiation.The present study indicated that the antheridioen system of D.uniformis differs from that of C. thalictroides.

OsLIS-L1 encoding a lissencephaly type-1-like protein with WD40 repeats is required for plant height and male gametophyte formation in rice

Although a large number of genes encoding the WD40 motif have been identified as being involved in various developmental processes in Arabidopsis, little is known about the function of these genes in rice (Oryza sativa). Here, we report the cloning and functional characterization of a novel rice gene OsLIS-L1 (Lissencephaly type-1-like 1), which is required for normal fertility and the first internode elongation. OsLIS-L1 encodes a lissencephaly type-1-like protein containing the WD40 motif that is required for brain development in human. SMART algorithm analysis indicated that OsLIS-L1 contains a LIS1 homology (LisH) domain, a C terminus to LisH (CTLH) domain, a five WD40-repeat domain in the middle, and a domain with four WD40 repeats which is homologous to the β subunit of trimeric G-proteins (G(β)). OsLIS-L1 transcript is relatively highly abundant in stem and panicle and has a dynamic expression pattern at different panicle developmental stages. Two independent alleles, designated oslis-l1-1 and oslis-l1-2, exhibited similar abnormal developmental phenotypes, including semi-dwarf, shorter panicle length, and reduced male fertility. Cytological examination confirmed that OsLIS-L1 does not affect the meiosis in pollen mother cells. Compared with wild type, the oslis-l1 mutant had abnormal male gametophyte formation, but anther cell wall and pollen wall development were not affected. Histological analysis revealed that OsLIS-L1 regulates the cell proliferation in the first internode under the panicle. Our results indicate that OsLIS-L1 plays an important role in male gametophyte formation and the first internode elongation in rice.

Conserved CDC20 Cell Cycle Functions Are Carried out by Two of the Five Isoforms in Arabidopsis thaliana

BackgroundThe CDC20 and Cdh1/CCS52 proteins are substrate determinants and activators of the Anaphase Promoting Complex/Cyclosome (APC/C) E3 ubiquitin ligase and as such they control the mitotic cell cycle by targeting the degradation of various cell cycle regulators. In yeasts and animals the main CDC20 function is the destruction of securin and mitotic cyclins. Plants have multiple CDC20 gene copies whose functions have not been explored yet. In Arabidopsis thaliana there are five CDC20 isoforms and here we aimed at defining their contribution to cell cycle regulation, substrate selectivity and plant development.Methodology/Principal FindingsStudying the gene structure and phylogeny of plant CDC20s, the expression of the five AtCDC20 gene copies and their interactions with the APC/C subunit APC10, the CCS52 proteins, components of the mitotic checkpoint complex (MCC) and mitotic cyclin substrates, conserved CDC20 functions could be assigned for AtCDC20.1 and AtCDC20.2. The other three intron-less genes were silent and specific for Arabidopsis. We show that AtCDC20.1 and AtCDC20.2 are components of the MCC and interact with mitotic cyclins with unexpected specificity. AtCDC20.1 and AtCDC20.2 are expressed in meristems, organ primordia and AtCDC20.1 also in pollen grains and developing seeds. Knocking down both genes simultaneously by RNAi resulted in severe delay in plant development and male sterility. In these lines, the meristem size was reduced while the cell size and ploidy levels were unaffected indicating that the lower cell number and likely slowdown of the cell cycle are the cause of reduced plant growth.Conclusions/SignificanceThe intron-containing CDC20 gene copies provide conserved and redundant functions for cell cycle progression in plants and are required for meristem maintenance, plant growth and male gametophyte formation. The Arabidopsis-specific intron-less genes are possibly “retrogenes” and have hitherto undefined functions or are pseudogenes.

Rice APOPTOSIS INHIBITOR5 Coupled with Two DEAD-Box Adenosine 5′-Triphosphate-Dependent RNA Helicases Regulates Tapetum Degeneration

Programmed cell death (PCD) during tapetum degeneration in postmeiotic anthers is critical for the proper development of male gametophytes in flowering plants. Although several genes involved in this process have been identified recently, the molecular mechanism is still poorly understood. Here, we show that knockout of rice (Oryza sativa) APOPTOSIS INHIBITOR5 (API5), which encodes a putative homolog of antiapoptosis protein Api5 in animals, results in delayed degeneration of the tapetum due to inhibition of the tapetal PCD process leading to defects in formation of male gametophytes. Os API5 is a nuclear protein that interacts with two DEAD-box ATP-dependent RNA helicases, API5-INTERACTING PROTEIN1 (AIP1) and AIP2. AIP1 and AIP2 are homologs of yeast (Saccharomyces cerevisiae) Suppressor of Bad Response to Refrigeration1 protein 2 (SUB2p) that have critical roles in transcription elongation and pre-mRNA splicing. Os AIP1 and AIP2 can form dimers and interact directly with the promoter region of CP1, a rice cysteine protease gene. Suppression of Os AIP1/2 leads to down-regulation of CP1, resulting in sterility, which is highly similar to the effects of suppressed expression of Os CP1. Our results uncover a previously unknown pathway for regulating PCD during tapetum degeneration in rice, one that may be conserved among eukaryotic organisms.

Effect of high temperatures in the pre-blooming and blooming periods on ovule formation, pollen grains and yield of ‘Granada’ peach

The aim of this work was to evaluate the effects of high temperatures in the pre-blooming and blooming periods on the growth of sexual gametes and yield of ‘Granada’ peach. The experiment was carried out in the commercial orchard of Charqueadas, under the subtropical conditions of the Central Depression at Rio Grande do Sul State, Brazil (28°57′S; 51°37′W; 30 m alt.). Two treatments were tested: (1) trees in the greenhouse with partial ventilation and (2) trees in the orchard. The phenology, morphologic constitutions of the pollen grains, ovule growth, yield and germination (%) of pollen grains and fruit set were evaluated. High temperatures in the pre-blooming and blooming periods anticipated the break of dormancy and blooming. These conditions also delayed the female gametophytes (embryo sac) and promoted anomalies in the formation of male gametophytes. Those factors promoted low pollen viability and a lack of synchrony in fertilization, thereby generating low fruit set percentages and yield.

Biochemical and structural aspects of induction and development of pollen-embryos inDatura

SummaryStructural changes and amino-acid metabolism during the induction and development of androgenesis were examined.The differences in amino-acid metabolism of pollen development in vivo i.e. male gametophyte formation and in vitro i.e. sporophyte formation were observed. Of mature pollen, proline formed 60% of the total amino-acid pool and had shown a consistant increment during pollen development. During the embryogenesis the level of threonine serine, glutamic acid and γ ABA increased while proline concentration decrease to a trace. At the plantlet, stage γ ABA and threonine + serine formed 56.5% of the total amino-acid pool. The different effects of amino-acids added in the culture medium were found.The ultrastruclural studies of the cultured anthers have shown the formation of two equal nuclei, their fusion and the formation of a diploid embryo. In certain cases the degeneration of the generative cell and the formation of embryo from the vegetative cell were observed. In the developing embryos, po...

Change in the amino-acid content during male gametophyte formation of Datura metel in Situ

Determination of the free and bound aminoacids during microsporogenesis of Datura metel showed that the principal amino-acids were proline, glutamic acid, aspartic acid, threonine-serine and alanine. Of these, only proline showed a consistent increment during pollen development. In contrast, aspartic acid and lysine decreased in the later stages of microsporogenesis. The amounts of other amino-acids did not show any consistent pattern. Four amino-acids, namely proline, glutamic acid and threonine-serine constituted nearly 85% of the free amino-acid pool in the developed anther (stage IV). Proline accumulation, relative to the total free amino-acid pool in mature anthers, was correlated with the water-content. The results were discussed in view of possible relationships between metabolic activity and free and bound amino-acid concentrations.