scholarly journals Embryo development in Carica papaya Linn

2021 ◽  
Author(s):  
Miguel Acevedo-Benavides ◽  
Pablo Bolaños-Villegas
Keyword(s):  
Cell Fate ◽  
Female Gametophyte ◽  
Carica Papaya ◽  
Genetic Regulation ◽  
Draft Genome ◽  
Embryo Sac ◽  
Egg Cell ◽  
Parental Line ◽  
Before And After ◽  
Autonomous Development

ABSTRACTPapaya (Carica papaya Linn.) is a tropical plant whose draft genome has been sequenced. Papaya produces large fruits rich in vitamins A and C and is an important cash crop in developing countries. Nonetheless, little is known about how the female gametophyte develops, how it is fertilized and how it develops into a mature seed containing an embryo and an endosperm. The Papaya female gametophyte displays a Polygonum-type architecture consisting of two synergid cells, an egg cell, a central cell, and three antipodal cells. Reports are available of the presumed existence of varieties in which cross fertilization is bypassed and autonomous development of embryos occurs (e.g., apomixis). In this study, we analyzed the development of female gametophytes in a commercial Hawaiian parental line and in the presumed apomictic Costa Rican line L1. Samples were collected before and after anthesis to compare the overall structure, size and transcriptional patterns of several genes that may be involved in egg and endosperm cell fate and proliferation. These genes were the putative papaya homologs of ARGONAUTE9 (AGO9), MEDEA (MEA), RETINOBLASTOMA RELATED-1 (RBR1), and SLOW WALKER-1 (SWA1). Our results suggest that its feasible to identify the contour of structural features of Polygonum-type development, and that in bagged female flowers of line L1 we might have observed autonomous development of embryo-like structures. Possible downregulation of papaya homologs for AGO9, MEA, RBR1 and SWA1 was observed in embryo sacs from line L1 before and after anthesis, which may suggest a tentative link between suspected apomixis and transcriptional downregulation of genes for RNA-directed DNA methylation, histone remodelers, and rRNA processing. Most notably, the large size of the papaya embryo sac suggests that it could be a cytological alternative to Arabidopsis thaliana for study. Significant variation in embryo sac size was observed between the varieties under study, suggesting wide differences in the genetic regulation of anatomical features.

scholarly journals Recent advances in understanding female gametophyte development

F1000Research ◽  
2018 ◽  
Vol 7 ◽  
pp. 804 ◽  
Author(s):  
Debra J Skinner ◽  
Venkatesan Sundaresan
Keyword(s):  
Cell Fate ◽  
Female Gametophyte ◽  
Cell Communication ◽  
Embryo Sac ◽  
Cell Types ◽  
Egg Cell ◽  
Male Gametes ◽  
Reproductive Unit ◽  
Genetic Mechanisms ◽  
Female Gametophyte Development

The haploid female gametophyte (embryo sac) is an essential reproductive unit of flowering plants, usually comprising four specialized cell types, including the female gametes (egg cell and central cell). The differentiation of these cells relies on spatial signals which pattern the gametophyte along a proximal-distal axis, but the molecular and genetic mechanisms by which cell identities are determined in the embryo sac have long been a mystery. Recent identification of key genes for cell fate specification and their relationship to hormonal signaling pathways that act on positional cues has provided new insights into these processes. A model for differentiation can be devised with egg cell fate as a default state of the female gametophyte and with other cell types specified by the action of spatially regulated factors. Cell-to-cell communication within the gametophyte is also important for maintaining cell identity as well as facilitating fertilization of the female gametes by the male gametes (sperm cells).

scholarly journals Transcriptional repression specifies the central cell for double fertilization

2020 ◽  
Vol 117 (11) ◽  
pp. 6231-6236 ◽  
Author(s):  
Meng-Xia Zhang ◽  
Shan-Shan Zhu ◽  
Yong-Chao Xu ◽  
Ya-Long Guo ◽  
Wei-Cai Yang ◽  
...  
Keyword(s):  
Cell Fate ◽  
Transcriptional Repression ◽  
Female Gametophyte ◽  
Embryo Sac ◽  
Central Cell ◽  
Egg Cell ◽  
Accessory Cell ◽  
Double Fertilization ◽  
Genetic Rescue ◽  
Key Innovation

Double fertilization is a key innovation for the evolutionary success of angiosperms by which the two fertilized female gametes, the egg cell and central cell, generate the embryo and endosperm, respectively. The female gametophyte (embryo sac) enclosed in the sporophyte is derived from a one-celled haploid cell lineage. It undergoes successive events of mitotic divisions, cellularization, and cell specification to give rise to the mature embryo sac, which contains the two female gametes accompanied by two types of accessory cells, namely synergids and antipodals. How the cell fate of the central cell is specified has long been equivocal and is further complicated by the structural diversity of female gametophyte across plant taxa. Here, MADS-box protein AGL80 was verified as a transcriptional repressor that directly suppresses the expression of accessory cell-specific genes to specify the central cell. Further genetic rescue and phylogenetic assay of the AGL80 orthologs revealed a possible conserved mechanism in the Brassicaceae family. Results from this study provide insight into the molecular determination of the second female gamete cell in Brassicaceae.

scholarly journals Phylogenetic and Expression Analysis of CENH3 and APOLLO Genes in Sexual and Apomictic Boechera Species

2021 ◽  
Author(s):  
Evgeny Bakin ◽  
Fatih Sezer ◽  
Aslıhan Özbilen ◽  
Irem Kilic ◽  
Buket Uner ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Genetic Regulation ◽  
Single Copy ◽  
Expression Level ◽  
Egg Cell ◽  
Copy Gene ◽  
Histone H3 Variant ◽  
Before And After ◽  
Spindle Microtubules ◽  
Mitosis And Meiosis

Apomictic plants (reproducing via asexual seeds), unlike sexual individuals, avoid meiosis and egg cell fertilization. Consequently, apomixis is very important for fixing maternal genotypes in the next plant generations. Despite the progress in the study of apomixis, molecular and genetic regulation of the latter remains poorly understood. So far APOLLO (Aspartate Glutamate Aspartate Aspartate histidine exonuclease) is one of the very few described genes associated with apomixis in Boechera species. The centromere-specific histone H3 variant encoded by CENH3 gene is essential for cell division. Mutations in CENH3 disrupt chromosome segregation during mitosis and meiosis since the attachment of spindle microtubules to a mutated form of the CENH3 histone fails. This paper presents in silico characteristic of APOLLO and CENH3 genes, which may affect apomixis. Also, we characterize the structure of CENH3, study expression levels of APOLLO and CENH3 in gynoecium/siliques of the natural diploid apomictic and sexual Boechera species at the stages of before and after fertilization. While CENH3 was a single copy gene in all Boechera species, the APOLLO gene have several polymorphic alleles associated with sexual and apomictic reproduction in the Boechera genera. Expression of the APOLLO apo-allele during meiosis was upregulated in gynoecium of apomict B. divaricarpa downregulating after meiosis until 4th day after pollination (DAP). On the 5th DAP, expression in apomictic siliques increased again. In sexual B. stricta gynoecium and siliques APOLLO apo-allele did not express. Expression of the APOLLO sex-allele during and after meiosis in gynoecium of sexual plants was several times higher than that in apomictic gynoecium. However, after pollination the sex-allele was downregulated in sexual siliques to the level of apomicts and increased sharply on the 5th DAP, while in apomictic siliques it almost did not express. At the meiotic stage, the expression level of CENH3 in the gynoecium of apomicts was two times lower than that of the sexual Boechera, decreasing in both species after meiosis and keep remaining very low in siliques of both species for several days after artificial pollination until the 4th DAP, when the expression level raised in sexual B. stricta siliques exceeding 5 times the level in apomictic B. divaricarpa siliques. We also discuss polymorphism and phylogeny of the APOLLO and CENH3 genes.

scholarly journals Phylogenetic and Expression Analysis of CENH3 and APOLLO Genes in Sexual and Apomictic Boechera Species

2021 ◽  
Author(s):  
Evgeny Bakin ◽  
Fatih Sezer ◽  
Irem Kilic ◽  
Aslıhan Özbilen ◽  
Mike Rayko ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Genetic Regulation ◽  
Single Copy ◽  
Egg Cell ◽  
Expression Levels ◽  
Histone H3 Variant ◽  
Before And After ◽  
Spindle Microtubules ◽  
Mitosis And Meiosis

Apomictic plants (reproducing via asexual seeds), unlike sexual individuals, avoid meiosis and egg cell fertilization. Consequently, apomixis is very important for fixing maternal genotypes in the next plant generations. Despite the progress in the study of apomixis, molecular and genetic regulation of the latter remains poorly understood. So far APOLLO (Aspartate Glutamate Aspartate Aspartate histidine exonuclease) is the only described gene associated with apomixis in Boechera species. The centromere-specific histone H3 variant encoded by CENH3 gene is essential for cell division. Mutations in CENH3 disrupt chromosome segregation during mitosis and meiosis since the attachment of spindle microtubules to a mutated form of the CENH3 histone fails. This paper presents in silico characteristic of APOLLO and CENH3 genes, which may affect apomixis. Also, in this research we characterize the structure of CENH3, study expression levels of CENH3 and APOLLO in gynoecium/siliques of the natural diploid apomictic and sexual Boechera species at the stages of before and after fertilization. At the premeiotic stage, the expression level of CENH3 in the gynoecium of apomicts was two times lower than that of the sexual Boechera, it decreased in both species by the time of meiosis and increased after fertilization. By 1 DAP CENH3 expression started dropping in sexual B. stricta siliques and kept increasing in apomictic B. divaricarpa ones. That might indicate to a role of CENH3 in apomictic development in Boechera species. The expression levels of APOLLO also sharply decreased by the time of meiosis in gynoecium of both species; however, by 3 DAP, the level of APOLLO expression in siliques of apomicts was almost 1.5 times higher than that of the sexuals. While CENH3 was a single copy gene in all Boechera species, the APOLLO gene have several polymorphic alleles associated with sexual and apomictic reproduction in the Boechera genera. We also discuss polymorphism and phylogeny of the APOLLO and CENH3 genes.

DEVELOPMENT OF THE EMBRYO SAC AND EMBRYO OF TEFF, ERAGROSTIS TEF

1966 ◽  
Vol 44 (8) ◽  
pp. 1071-1075 ◽  
Author(s):  
Melak H. Mengesha ◽  
A. T. Guard
Keyword(s):  
Female Gametophyte ◽  
Leaf Blade ◽  
Floral Development ◽  
Flag Leaf ◽  
Embryo Sac ◽  
Eragrostis Tef ◽  
Careful Study ◽  
Embryo Formation ◽  
Self Pollination ◽  
Before And After

A careful study of the floral development of Eragrostis tef indicates that the flowers do not open and that self-pollination is the rule. Observations of the development of the female gametophyte show that it is of the normal monosporic type common to most angiosperms. The three antipodals divide several times as is common in grasses. Study of many ovules before and after fertilization showed absence of any apomictic type of embryo formation. Fertilization was found to occur in the basal floret of a spikelet when that floret was at the base of the flag leaf blade.

A cytoembryological study of Agrostis pilosula

1976 ◽  
Vol 54 (21) ◽  
pp. 2490-2496 ◽  
Author(s):  
M. Muniyamma
Keyword(s):  
Mother Cell ◽  
Female Gametophyte ◽  
Lateral Displacement ◽  
Embryo Sac ◽  
First Record ◽  
Mature Female ◽  
Egg Cell ◽  
Hormonal Imbalance ◽  
Endosperm Starch ◽  
Female Gametophyte Development

A detailed investigation of microsporogenesis, megasporogenesis, female gametophyte development, and embryogeny in Agrostis pilosula Trin. has been made. The chromosome number of 2n = 44 is the first record for this species. Pollen mother cell meiosis reveals normal chromosome behaviour. Microspore tetrads are mostly isobilateral. The bitegmic ovule is initially anatropous and becomes hemianatropous. The inner integument delimits the micropyle. A single archesporial cell, which is hypodermal or, more rarely, deeply seated in origin, directly functions as the megaspore mother cell. Meiosis usually results in the formation of a T-shaped tetrad of megaspores, but occasionally a linear triad of megaspores is seen instead. After three mitotic divisions, the chalazal megaspore gives rise to an eight-nucleate embryo sac. The mature female gametophyte is atypical because of the lateral displacement of antipodals and its triangular shape. It consists of two synergids, a pear-shaped egg slightly pushed aside, fused polar nuclei in close approximation to the egg cell, and three large ballooned laterally displaced coenocytic antipodal cells with hypertrophied nuclei. This antipodal condition might be associated with hormonal imbalance. The endosperm is free nuclear at first and leads to the formation of solid endosperm. Starch grains are observed in older cells of endosperm. The embryo development is regular and conforms to Pooid type.

scholarly journals Plant egg cell fate determination depends on its exact position in female gametophyte

2021 ◽  
Vol 118 (8) ◽  
pp. e2017488118 ◽  
Author(s):  
Yang Sun ◽  
Xiu Wang ◽  
Lin Pan ◽  
Fei Xie ◽  
Bo Dai ◽  
...  
Keyword(s):  
Cell Fate ◽  
Sperm Cell ◽  
Female Gametophyte ◽  
Imaging System ◽  
Egg Cell ◽  
Cell Identity ◽  
Auxin Level ◽  
Egg Apparatus

Plant fertilization involves both an egg cell, which fuses with a sperm cell, and synergid cells, which guide pollen tubes for sperm cell delivery. Therefore, egg and synergid cell functional specifications are prerequisites for successful fertilization. However, how the egg and synergid cells, referred to as the “egg apparatus,” derived from one mother cell develop into distinct cell types remains an unanswered question. In this report, we show that the final position of the nuclei in female gametophyte determines the cell fate of the egg apparatus. We established a live imaging system to visualize the dynamics of nuclear positioning and cell identity establishment in the female gametophyte. We observed that free nuclei should migrate to a specific position before egg apparatus specialization. Artificial changing in the nuclear position on disturbance of the actin cytoskeleton, either in vitro or in vivo, could reset the cell fate of the egg apparatus. We also found that nuclei of the same origin moved to different positions and then showed different cell identities, whereas nuclei of different origins moved to the same position showed the same cell identity, indicating that the final positions of the nuclei, rather than specific nucleus lineage, play critical roles in the egg apparatus specification. Furthermore, the active auxin level was higher in the egg cell than in synergid cells. Auxin transport inhibitor could decrease the auxin level in egg cells and impair egg cell identity, suggesting that directional and accurate auxin distribution likely acts as a positional cue for egg apparatus specialization.

Fertilization in Plumbago zeylanica: entry and discharge of the pollen tube in the embryo sac

1982 ◽  
Vol 60 (11) ◽  
pp. 2219-2230 ◽  
Author(s):  
Scott D. Russell
Keyword(s):  
Cell Wall ◽  
Pollen Tube ◽  
Female Gametophyte ◽  
Embryo Sac ◽  
Central Cell ◽  
Vegetative Nucleus ◽  
Egg Cell ◽  
Ultrastructural Organization ◽  
Plumbago Zeylanica ◽  
Male Gametes

The ultrastructural organization of the megagametophyte of Plumbago zeylanica, which lacks synergids, was examined in chemically and physically fixed ovules after entry of the pollen tube. Similar to angiosperms with conventionally organized megagametophytes, the pollen tube enters the ovule through a micropyle, formed by the inner integument, and approaches the female gametophyte by growing between nucellar cells. Unlike other described female gametophytes, however, continued pollen tube growth results in direct penetration of the base of the egg through cell wall projections forming a filiform apparatus and is completed between the egg and central cell without disrupting either of these cells' plasma membranes. A terminal pollen tube aperture forms when the pollen tube reaches an area of strong curvature near the summit of the egg; this results in the release of two sperm cells, the vegetative nucleus, and a limited amount of pollen cytoplasm. The formerly continuous chalazal egg cell wall is locally disrupted near the tip of the pollen tube and apparently is thus modified for reception of male gametes. Discharged pollen cytoplasm rapidly degenerates between the egg and central cell, but unlike pollen tube discharge in conventionally organized megagametophytes, it is unassociated with the degeneraton of any receptor cell within the female gametophyte. Sperm nuclei are transmitted, one to the egg and the other to the central cell, to effect double fertilization by nuclear fusion with their respective female reproductive nuclei. The vegetative nucleus and discharged pollen cytoplasm degenerate between the developing embryo and endosperm during early embryogenesis. The emerging concept that the egg of Plumbago possesses combined egg and synergid functions is supported by the present study and suggests that the megagametophyte of this plant displays a highly specialized egg apparatus composed exclusively of a single, modified egg cell.

scholarly journals Dynamics of the cell fate specifications during female gametophyte development in Arabidopsis

PLoS Biology ◽  
2021 ◽  
Vol 19 (3) ◽  
pp. e3001123
Author(s):  
Daichi Susaki ◽  
Takamasa Suzuki ◽  
Daisuke Maruyama ◽  
Minako Ueda ◽  
Tetsuya Higashiyama ◽  
...  
Keyword(s):  
Gene Expression ◽  
Cell Fate ◽  
Female Gametophyte ◽  
Nuclear Division ◽  
Cell Plate ◽  
Egg Cell ◽  
Specific Gene ◽  
Cell Plate Formation ◽  
Plate Formation ◽  
Female Gametophyte Development

The female gametophytes of angiosperms contain cells with distinct functions, such as those that enable reproduction via pollen tube attraction and fertilization. Although the female gametophyte undergoes unique developmental processes, such as several rounds of nuclear division without cell plate formation and final cellularization, it remains unknown when and how the cell fate is determined during development. Here, we visualized the living dynamics of female gametophyte development and performed transcriptome analysis of individual cell types to assess the cell fate specifications in Arabidopsis thaliana. We recorded time lapses of the nuclear dynamics and cell plate formation from the 1-nucleate stage to the 7-cell stage after cellularization using an in vitro ovule culture system. The movies showed that the nuclear division occurred along the micropylar–chalazal (distal–proximal) axis. During cellularization, the polar nuclei migrated while associating with the forming edge of the cell plate, and then, migrated toward each other to fuse linearly. We also tracked the gene expression dynamics and identified that the expression of MYB98pro::GFP–MYB98, a synergid-specific marker, was initiated just after cellularization in the synergid, egg, and central cells and was then restricted to the synergid cells. This indicated that cell fates are determined immediately after cellularization. Transcriptome analysis of the female gametophyte cells of the wild-type and myb98 mutant revealed that the myb98 synergid cells had egg cell–like gene expression profiles. Although in myb98, egg cell–specific gene expression was properly initiated in the egg cells only after cellularization, but subsequently expressed ectopically in one of the 2 synergid cells. These results, together with the various initiation timings of the egg cell–specific genes, suggest complex regulation of the individual gametophyte cells, such as cellularization-triggered fate initiation, MYB98-dependent fate maintenance, cell morphogenesis, and organelle positioning. Our system of live-cell imaging and cell type–specific gene expression analysis provides insights into the dynamics and mechanisms of cell fate specifications in the development of female gametophytes in plants.

scholarly journals Dynamics of the cell fate specifications during female gametophyte development in Arabidopsis

2020 ◽  
Author(s):  
Daichi Susaki ◽  
Takamasa Suzuki ◽  
Daisuke Maruyama ◽  
Minako Ueda ◽  
Tetsuya Higashiyama ◽  
...  
Keyword(s):  
Gene Expression ◽  
Cell Fate ◽  
Female Gametophyte ◽  
Nuclear Division ◽  
Cell Plate ◽  
Egg Cell ◽  
Specific Gene ◽  
Cell Plate Formation ◽  
Plate Formation ◽  
Female Gametophyte Development

ABSTRACTThe female gametophytes of angiosperms contain cells with distinct functions, such as those that enable reproduction via pollen tube attraction and fertilization. Although the female gametophyte undergoes unique developmental processes, such as several rounds of nuclear division without cell plate formation, and the final cellularization, it remains unknown when and how the cell fate is determined during their development. Here, we visualized the living dynamics of female gametophyte development and performed transcriptome analysis of its individual cell types, to assess the cell fate specifications in Arabidopsis thaliana. We recorded time lapses of the nuclear dynamics and cell plate formation from the one-nucleate stage to the seven-cell stage after cellularization, using the in vitro ovule culture system. The movies showed that the nuclear division occurred along the micropylar–chalazal axis. During cellularization, the polar nuclei migrated while associating with forming edge of the cell plate. Then, each polar nucleus migrated to fuse linearly towards each other. We also tracked the gene expression dynamics and identified that the expression of the MYB98pro∷GFP, a synergid-specific marker, was initiated before cellularization, and then restricted to the synergid cells after cellularization. This indicated that cell fates are determined immediately after cellularization. Transcriptome analysis of the female gametophyte cells of the wild type and myb98 mutant, revealed that the myb98 synergid cells had the egg cell-like gene expression profile. Although in the myb98, the egg cell-specific gene expressions were properly initiated only in the egg cells after cellularization, but subsequently expressed ectopically in one of the two synergid cells. These results, together with the various initiation timings of the egg cell-specific genes suggest the complex regulation of the individual gametophyte cells, such as cellularization-triggered fate initiation, MYB98-dependent fate maintenance, cell morphogenesis, and organelle positioning. Our system of live-cell imaging and cell-type-specific gene expression analysis provides insights into the dynamics and mechanisms of cell fate specifications in the development of female gametophytes in plants.

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