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PLoS Biology Mar 2021The female gametophytes of angiosperms contain cells with distinct functions, such as those that enable reproduction via pollen tube attraction and fertilization....
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.
Topics: Arabidopsis; Arabidopsis Proteins; Cell Differentiation; Cell Nucleus; Cytoplasm; Gene Expression; Gene Expression Profiling; Gene Expression Regulation, Plant; Magnoliopsida; Morphogenesis; Ovule; Pollen Tube; Promoter Regions, Genetic; Transcription Factors; Transcriptome
PubMed: 33770073
DOI: 10.1371/journal.pbio.3001123 -
Nature Communications Jan 2023Pollen tube guidance within female tissues of flowering plants can be divided into preovular guidance, ovular guidance and a connecting stage called pollen tube...
Pollen tube guidance within female tissues of flowering plants can be divided into preovular guidance, ovular guidance and a connecting stage called pollen tube emergence. As yet, no female factor has been identified to positively regulate this transition process. In this study, we show that an ovary-expressed bHLH transcription factor Cucumis sativus ALCATRAZ (CsALC) functions in pollen tube emergence in cucumber. CsALC knockout mutants showed diminished pollen tube emergence, extremely reduced entry into ovules, and a 95% reduction in female fertility. Further examination showed two rapid alkalinization factors CsRALF4 and CsRALF19 were less expressed in Csalc ovaries compared to WT. Besides the loss of male fertility derived from precocious pollen tube rupture as in Arabidopsis, Csralf4 Csralf19 double mutants exhibited a 60% decrease in female fertility due to reduced pollen tube distribution and decreased ovule targeting efficiency. In brief, CsALC regulates female fertility and promotes CsRALF4/19 expression in the ovary during pollen tube guidance in cucumber.
Topics: Cucumis sativus; Ovary; Pollen Tube; Arabidopsis; Arabidopsis Proteins; Ovule
PubMed: 36650145
DOI: 10.1038/s41467-023-35936-z -
BMC Plant Biology Jan 2022In plants, a critical balance between differentiation and proliferation of stem cells at the shoot apical meristem zone is essential for proper growth. The...
BACKGROUND
In plants, a critical balance between differentiation and proliferation of stem cells at the shoot apical meristem zone is essential for proper growth. The spatiotemporal regulation of some crucial genes dictates the formation of a boundary within and around budding organs. The boundary plays a pivotal role in distinguishing one tissue type from another and provides a defined shape to the organs at their developed stage. NAM/CUC subfamily of the NAC transcription factors control the boundary formation during meristematic development.
RESULTS
Here, we have identified the CUP-SHAPED COTYLEDON (CUC) genes in sugarcane and named SsCUC2 (for the orthologous gene of CUC1 and CUC2) and SsCUC3. The phylogenetic reconstruction showed that SsCUCs occupy the CUC2 and CUC3 clade together with monocots, whereas eudicot CUC2 and CUC3 settled separately in the different clade. The structural analysis of CUC genes showed that most of the CUC3 genes were accompanied by an intron gain during eudicot divergence. Besides, the study of SsCUCs expression in the RNA-seq obtained during different stages of ovule development revealed that SsCUCs express in developing young tissues, and the expression of SsCUC2 is regulated by miR164. We also demonstrate that SsCUC2 (a monocot) could complement the cuc2cuc3 mutant phenotype of Arabidopsis (eudicot).
CONCLUSIONS
This study further supports that CUC2 has diverged in CUC1 and CUC2 during the evolution of monocots and eudicots from ancestral plants. The functional analysis of CUC expression patterns during sugarcane ovule development and ectopic expression of SsCUC2 in Arabidopsis showed that SsCUC2 has a conserved role in boundary formation. Overall, these findings improve our understanding of the functions of sugarcane CUC genes. Our results reveal the crucial functional role of CUC genes in sugarcane.
Topics: Arabidopsis; Arabidopsis Proteins; Cotyledon; Gene Expression Regulation, Plant; Genetic Complementation Test; Meristem; MicroRNAs; Mutation; Ovule; Phenotype; Phylogeny; Plant Proteins; Plants, Genetically Modified; Saccharum; Transcription Factors
PubMed: 35065620
DOI: 10.1186/s12870-022-03440-z -
PLoS Genetics Jan 2018Ovules are fundamental for plant reproduction and crop yield as they are the precursors of seeds. Therefore, ovule specification is a critical developmental program. In...
Ovules are fundamental for plant reproduction and crop yield as they are the precursors of seeds. Therefore, ovule specification is a critical developmental program. In Arabidopsis thaliana, ovule identity is redundantly conferred by the homeotic D-class genes SHATTERPROOF1 (SHP1), SHP2 and SEEDSTICK (STK), phylogenetically related to the MADS-domain regulatory gene AGAMOUS (AG), essential in floral organ specification. Previous studies have shown that the HUA-PEP activity, comprised of a suite of RNA-binding protein (RBP) encoding genes, regulates AG pre-mRNA processing and thus flower patterning and organ identity. Here, we report that the HUA-PEP activity additionally governs ovule morphogenesis. Accordingly, in severe hua-pep backgrounds ovules transform into flower organ-like structures. These homeotic transformations are most likely due to the dramatic reduction in SHP1, SHP2 and STK activity. Our molecular and genome-wide profiling strategies revealed the accumulation of prematurely terminated transcripts of D-class genes in hua-pep mutants and reduced amounts of their respective functional messengers, which points to pre-mRNA processing misregulation as the origin of the ovule developmental defects in such backgrounds. RNA processing and transcription are coordinated by the RNA polymerase II (RNAPII) carboxyl-terminal domain (CTD). Our results show that HUA-PEP activity members can interact with the CTD regulator C-TERMINAL DOMAIN PHOSPHATASE-LIKE1 (CPL1), supporting a co-transcriptional mode of action for the HUA-PEP activity. Our findings expand the portfolio of reproductive developmental programs in which HUA-PEP activity participates, and further substantiates the importance of RNA regulatory mechanisms (pre-mRNA co-transcriptional regulation) for correct gene expression during plant morphogenesis.
Topics: Arabidopsis; Cell Differentiation; Flowers; Gene Expression Regulation, Developmental; Gene Expression Regulation, Plant; Genes, Plant; Morphogenesis; Ovule; Plants, Genetically Modified; RNA Precursors; RNA Processing, Post-Transcriptional; RNA-Binding Proteins; Transcription Factors
PubMed: 29329291
DOI: 10.1371/journal.pgen.1007182 -
Molecular Plant Sep 2022Distinct from the motile flagellated sperm of animals and early land plants, the non-motile sperm cells of flowering plants are carried in the pollen grain to the female...
Distinct from the motile flagellated sperm of animals and early land plants, the non-motile sperm cells of flowering plants are carried in the pollen grain to the female pistil. After pollination, a pair of sperm cells are delivered into the embryo sac by pollen tube growth and rupture. Unlike other walled plant cells with an equilibrium between internal turgor pressure and mechanical constraints of the cell walls, sperm cells wrapped inside the cytoplasm of a pollen vegetative cell have only thin and discontinuous cell walls. The sperm cells are uniquely ellipsoid in shape, although it is unclear how they maintain this shape within the pollen tubes and after release. In this study, we found that genetic disruption of three endomembrane-associated cation/H exchangers specifically causes sperm cells to become spheroidal in hydrated pollens of Arabidopsis. Moreover, the released mutant sperm cells are vulnerable and rupture before double fertilization, leading to failed seed set, which can be partially rescued by depletion of the sperm-expressed vacuolar water channel. These results suggest a critical role of cell-autonomous osmoregulation in adjusting the sperm cell shape for successful double fertilization in flowering plants.
Topics: Animals; Arabidopsis; Arabidopsis Proteins; Fertilization; Magnoliopsida; Osmoregulation; Ovule; Pollen Tube; Seeds; Spermatozoa
PubMed: 35918896
DOI: 10.1016/j.molp.2022.07.013 -
Plant Physiology Jun 2021Reproductive isolation is a prerequisite to form and maintain a new species. Multiple prezygotic and postzygotic reproductive isolation barriers have been reported in...
Reproductive isolation is a prerequisite to form and maintain a new species. Multiple prezygotic and postzygotic reproductive isolation barriers have been reported in plants. In the model plant, Arabidopsis thaliana conspecific pollen tube precedence controlled by AtLURE1/PRK6-mediated signaling has been recently reported as a major prezygotic reproductive isolation barrier. By accelerating emergence of own pollen tubes from the transmitting tract, A. thaliana ovules promote self-fertilization and thus prevent fertilization by a different species. Taking advantage of a septuple atlure1null mutant, we now report on the role of AtLURE1/PRK6-mediated signaling for micropylar pollen tube guidance. Compared with wild-type (WT) ovules, atlure1null ovules displayed remarkably reduced micropylar pollen tube attraction efficiencies in modified semi-in vivo A. thaliana ovule targeting assays. However, when prk6 mutant pollen tubes were applied, atlure1null ovules showed micropylar attraction efficiencies comparable to that of WT ovules. These findings indicate that AtLURE1/PRK6-mediated signaling regulates micropylar pollen tube attraction in addition to promoting emergence of own pollen tubes from the transmitting tract. Moreover, semi-in vivo ovule targeting competition assays with the same amount of pollen grains from both A. thaliana and Arabidopsis lyrata showed that A. thaliana WT and xiuqiu mutant ovules are mainly targeted by own pollen tubes and that atlure1null mutant ovules are also entered to a large extent by A. lyrata pollen tubes. Taken together, we report that AtLURE1/PRK6-mediated signaling promotes conspecific micropylar pollen tube attraction representing an additional prezygotic isolation barrier.
Topics: Arabidopsis; Arabidopsis Proteins; Mutation; Ovule; Pollen; Pollen Tube; Pollination; Protein Serine-Threonine Kinases; Reproductive Isolation; Signal Transduction
PubMed: 33638984
DOI: 10.1093/plphys/kiab105 -
Poultry Science Nov 1985Studies were conducted to investigate the effect of ovine luteinizing hormone (LH) treatment on steroid and LH secretion and ovulation in intact, saline-primed hens and... (Comparative Study)
Comparative Study
Studies were conducted to investigate the effect of ovine luteinizing hormone (LH) treatment on steroid and LH secretion and ovulation in intact, saline-primed hens and in pregnant mare serum gonadotropin (PMSG)-primed hens. Intact, saline-primed hens, injected 12 hr prior to the first (C1) ovulation of the sequence, responded with fully potentiated preovulatory surges of progesterone (P4) (peak value was 371% above preinjection values), estradiol-17 beta (E2) (117% above baseline), LH (220% above baseline), and premature ovulation. By comparison, those hens injected at the same time prior to the second (C2) ovulation responded with a lesser increase in plasma P4 (peak value was 305% above baseline) and E2 (72% above baseline), and there was no significant increase in plasma LH. Within this group, 4 of 5 hens failed to ovulate prematurely. All groups of PMSG-primed hens had significantly higher preinjection concentrations of P4 and E2, and lower basal concentrations of LH, compared to saline-primed hens. Subsequent to treatment of PMSG-primed hens with 25 or 100 micrograms ovine LH, there was a significant increase in plasma P4 to approximately 200% above preinjection concentrations. By contrast, there was a nonsignificant increase in plasma LH (50% above baseline values) and no significant increase in plasma E2. The ovulatory response following PMSG-priming was greatest in hens injected with 100 micrograms ovine LH (5 of 5 hens ovulated), while 3 of 5 hens injected with 25 micrograms ovine LH and 6 of 6 saline-challenged hens failed to ovulate.(ABSTRACT TRUNCATED AT 250 WORDS)
Topics: Animals; Chickens; Estradiol; Female; Gonadotropins, Equine; Luteinizing Hormone; Ovulation; Progesterone; Sheep
PubMed: 4070147
DOI: 10.3382/ps.0642171 -
American Journal of Botany Mar 2016Ecologists and evolutionary biologists have been interested in the functional biology of pollen since the discovery in the 1800s that pollen grains encompass tiny plants... (Review)
Review
Ecologists and evolutionary biologists have been interested in the functional biology of pollen since the discovery in the 1800s that pollen grains encompass tiny plants (male gametophytes) that develop and produce sperm cells. After the discovery of double fertilization in flowering plants, botanists in the early 1900s were quick to explore the effects of temperature and maternal nutrients on pollen performance, while evolutionary biologists began studying the nature of haploid selection and pollen competition. A series of technical and theoretic developments have subsequently, but usually separately, expanded our knowledge of the nature of pollen performance and how it evolves. Today, there is a tremendous diversity of interests that touch on pollen performance, ranging from the ecological setting on the stigma, structural and physiological aspects of pollen germination and tube growth, the form of pollen competition and its role in sexual selection in plants, virus transmission, mating system evolution, and inbreeding depression. Given the explosion of technical knowledge of pollen cell biology, computer modeling, and new methods to deal with diversity in a phylogenetic context, we are now more than ever poised for a new era of research that includes complex functional traits that limit or enhance the evolution of these deceptively simple organisms.
Topics: Biological Evolution; Ecological and Environmental Phenomena; Haploidy; Inbreeding; Ovule; Pollen
PubMed: 26980838
DOI: 10.3732/ajb.1600074 -
The New Phytologist Dec 2021Generally, in gymnosperms, pollination and fertilization events are temporally separated and the developmental processes leading the switch from ovule integument into...
Generally, in gymnosperms, pollination and fertilization events are temporally separated and the developmental processes leading the switch from ovule integument into seed coat are still unknown. The single ovule integument of Ginkgo biloba acquires the typical characteristics of the seed coat long before the fertilization event. In this study, we investigated whether pollination triggers the transformation of the ovule integument into the seed coat. Transcriptomics and metabolomics analyses performed on ovules just prior and after pollination lead to the identification of changes occurring in Ginkgo ovules during this specific time. A morphological atlas describing the developmental stages of ovule development is presented. The metabolic pathways involved in the lignin biosynthesis and in the production of fatty acids are activated upon pollination, suggesting that the ovule integument starts its differentiation into a seed coat before the fertilization. Omics analyses allowed an accurate description of the main changes that occur in Ginkgo ovules during the pollination time frame, suggesting the crucial role of the pollen arrival on the progression of ovule development.
Topics: Ginkgo biloba; Ovule; Pollen; Pollination; Seeds
PubMed: 34558676
DOI: 10.1111/nph.17753 -
Journal of Experimental Botany Nov 2022Cytokinin is considered to be an important driver of seed yield. To increase the yield of cotton while avoiding the negative consequences caused by constitutive...
Cytokinin is considered to be an important driver of seed yield. To increase the yield of cotton while avoiding the negative consequences caused by constitutive overproduction of cytokinin, we down-regulated specifically the carpel genes for cytokinin oxidase/dehydrogenase (CKX), a key negative regulator of cytokinin levels, in transgenic cotton. The carpel-specific down-regulation of CKXs significantly enhanced cytokinin levels in the carpels. The elevated cytokinin promoted the expression of carpel- and ovule-development-associated genes, GhSTK2, GhAG1, and GhSHP, boosting ovule formation and thus producing more seeds in the ovary. Field experiments showed that the carpel-specific increase of cytokinin significantly increased both seed yield and fiber yield of cotton, without resulting in detrimental phenotypes. Our study details the regulatory mechanism of cytokinin signaling for seed development, and provides an effective and feasible strategy for yield improvement of seed crops.
Topics: Down-Regulation; Seeds; Cytokinins; Ovule; Gene Expression Regulation, Plant; Cotton Fiber
PubMed: 35792654
DOI: 10.1093/jxb/erac303