-
International Journal of Molecular... Mar 2021Angiosperm reproduction relies on the precise growth of the pollen tube through different pistil tissues carrying two sperm cells into the ovules' embryo sac, where they... (Review)
Review
Angiosperm reproduction relies on the precise growth of the pollen tube through different pistil tissues carrying two sperm cells into the ovules' embryo sac, where they fuse with the egg and the central cell to accomplish double fertilization and ultimately initiate seed development. A network of intrinsic and tightly regulated communication and signaling cascades, which mediate continuous interactions between the pollen tube and the sporophytic and gametophytic female tissues, ensures the fast and meticulous growth of pollen tubes along the pistil, until it reaches the ovule embryo sac. Most of the pollen tube growth occurs in a specialized tissue-the transmitting tract-connecting the stigma, the style, and the ovary. This tissue is composed of highly secretory cells responsible for producing an extensive extracellular matrix. This multifaceted matrix is proposed to support and provide nutrition and adhesion for pollen tube growth and guidance. Insights pertaining to the mechanisms that underlie these processes remain sparse due to the difficulty of accessing and manipulating the female sporophytic tissues enclosed in the pistil. Here, we summarize the current knowledge on this key step of reproduction in flowering plants with special emphasis on the female transmitting tract tissue.
Topics: Extracellular Matrix; Fertilization; Flowers; Magnoliopsida; Ovule; Plant Proteins; Pollen Tube; Seeds; Signal Transduction
PubMed: 33807566
DOI: 10.3390/ijms22052603 -
Planta May 2023Arabidopsis GR1 and NTRA function in pollen tube penetrating the stigma into the transmitting tract during pollination. During pollination, recognition between pollen...
Arabidopsis GR1 and NTRA function in pollen tube penetrating the stigma into the transmitting tract during pollination. During pollination, recognition between pollen (tube) and stigma mediates the hydration and germination of pollen, as well as the growth of the pollen tube on the stigma. Arabidopsis glutathione reductase 1 (GR1) and NADPH-dependent thioredoxin reductase A (NTRA) are involved in regulating cell redox hemostasis. Both GR1 and NTRA are expressed in pollen, but their roles in pollen germination and the growth of the pollen tube need further investigation. In this study, we performed pollination experiments and found that the Arabidopsis gr1/ + ntra/- and gr1/- ntra/ + double mutation compromised the transmission of male gametophytes. Pollen morphology and viability of the mutants did not show obvious abnormalities. Additionally, the pollen hydration and germination of the double mutants on solid pollen germination medium were comparable to those of the wild type. However, the pollen tubes with gr1 ntra double mutation were unable to penetrate the stigma and enter the transmitting tract when they grew on the surface of the stigma. Our results indicate that GR1 and NTRA play a role in regulating the interaction between the pollen tube and the stigma during pollination.
Topics: Arabidopsis; Arabidopsis Proteins; Glutathione Reductase; Pollen Tube; Pollination; Thioredoxin-Disulfide Reductase; Cell Cycle Proteins
PubMed: 37208536
DOI: 10.1007/s00425-023-04161-9 -
Plant Physiology Jun 2020To reach the female gametophyte, growing pollen tubes must penetrate different tissues within the pistil, the female reproductive organ of a flower. Past research has...
To reach the female gametophyte, growing pollen tubes must penetrate different tissues within the pistil, the female reproductive organ of a flower. Past research has identified various chemotropic cues that guide pollen tubes through the transmitting tract of the pistil, which represents the longest segment of its growth path. In addition, physical mechanisms also play a role in pollen tube guidance; however, these processes remain poorly understood. Here we show that pollen tubes from plants with solid transmitting tracts actively respond to the stiffness of the environment. We found that pollen tubes from and other plant species with a solid or semisolid transmitting tract increase their growth rate in response to an increasing matrix stiffness. By contrast, pollen tubes from and other plant species with a hollow transmitting tract decrease their growth rate with increasing matrix stiffness, even though the forces needed to maintain a constant growth rate remain far below the maximum penetration force these pollen tubes are able to generate. Moreover, when confronted with a transition from a softer to a stiffer matrix, pollen tubes from display a greater ability to penetrate into a stiffer matrix compared with pollen tubes from even though the maximum force generated by pollen tubes from (11 µN) is smaller than the maximum force generated by pollen tubes from (36 µN). These findings demonstrate a mechano-sensitive growth behavior, termed here durotropic growth, that is only expressed in pollen tubes from plants with a solid or semisolid transmitting tract and thus may contribute to an effective pollen tube guidance within the pistil.
Topics: Flowers; Lilium; Plant Proteins; Pollen Tube; Nicotiana
PubMed: 32241878
DOI: 10.1104/pp.19.01505 -
Frontiers in Cell and Developmental... 2020Pollen germination and pollen tube growth are important biological events in the sexual reproduction of higher plants, during which a large number of vesicle trafficking... (Review)
Review
Pollen germination and pollen tube growth are important biological events in the sexual reproduction of higher plants, during which a large number of vesicle trafficking and membrane fusion events occur. When secretory vesicles are transported via the F-actin network in proximity to the apex of the pollen tube, the secretory vesicles are tethered and fused to the plasma membrane by tethering factors and SNARE proteins, respectively. The coupling and uncoupling between the vesicle membrane and plasma membrane are also regulated by dynamic cytoskeleton, proteins, and signaling molecules, including small G proteins, calcium, and PIP2. In this review, we focus on the current knowledge regarding secretory vesicle delivery, tethering, and fusion during pollen germination and tube growth and summarize the progress in research on how regulators and signaling molecules participate in the above processes.
PubMed: 33553150
DOI: 10.3389/fcell.2020.615447 -
Frontiers in Plant Science 2023
PubMed: 37496862
DOI: 10.3389/fpls.2023.1242416 -
Plant & Cell Physiology Nov 2021Many plant processes occur in the context of and in interaction with a surrounding matrix such as soil (e.g. root growth and root-microbe interactions) or surrounding... (Review)
Review
Many plant processes occur in the context of and in interaction with a surrounding matrix such as soil (e.g. root growth and root-microbe interactions) or surrounding tissues (e.g. pollen tube growth through the pistil), making it difficult to study them with high-resolution optical microscopy. Over the past decade, microfabrication techniques have been developed to produce experimental systems that allow researchers to examine cell behavior in microstructured environments that mimic geometrical, physical and/or chemical aspects of the natural growth matrices and that cannot be generated using traditional agar plate assays. These microfabricated environments offer considerable design flexibility as well as the transparency required for high-resolution, light-based microscopy. In addition, microfluidic platforms have been used for various types of bioassays, including cellular force assays, chemoattraction assays and electrotropism assays. Here, we review the recent use of microfluidic devices to study plant cells and organs, including plant roots, root hairs, moss protonemata and pollen tubes. The increasing adoption of microfabrication techniques by the plant science community may transform our approaches to investigating how individual plant cells sense and respond to changes in the physical and chemical environment.
Topics: Biological Assay; Bryophyta; Imaging, Three-Dimensional; Microfluidic Analytical Techniques; Plant Cells; Plant Roots; Pollen Tube; Protoplasts
PubMed: 34027549
DOI: 10.1093/pcp/pcab067 -
Frontiers in Plant Science 2023In flowering plants, pollination, pollen tube growth, and fertilization are regarded as the first hierarchical processes of producing offspring. However, their...
In flowering plants, pollination, pollen tube growth, and fertilization are regarded as the first hierarchical processes of producing offspring. However, their independent contributions to fruit set and development remain unclear. In this study, we examined the effect of three different types of pollen, intact pollen (IP), soft X-ray-treated pollen (XP) and dead pollen (DP), on pollen tube growth, fruit development and gene expression in "Micro-Tom" tomato. Normal germination and pollen tube growth were observed in flowers pollinated with IP; pollen tubes started to penetrate the ovary at 9 h after pollination, and full penetration was achieved after 24 h (IP24h), resulting in ~94% fruit set. At earlier time points (3 and 6 h after pollination; IP3h and IP6h, respectively), pollen tubes were still in the style, and no fruit set was observed. Flowers pollinated with XP followed by style removal after 24 h (XP24h) also demonstrated regular pollen tubes and produced parthenocarpic fruits with ~78% fruit set. As expected, DP could not germinate and failed to activate fruit formation. Histological analysis of the ovary at 2 days after anthesis (DAA) revealed that IP and XP comparably increased cell layers and cell size; however, mature fruits derived from XP were significantly smaller than those derived from IP. Furthermore, there was a high correlation between seed number and fruit size in fruit derived from IP, illustrating the crucial role of fertilization in the latter stages of fruit development. RNA-Seq analysis was carried out in ovaries derived from IP6h, IP24h, XP24h and DP24h in comparison with emasculated and unpollinated ovaries (E) at 2 DAA. The results revealed that 65 genes were differentially expressed (DE) in IP6h ovaries; these genes were closely associated with cell cycle dormancy release pathways. Conversely, 5062 and 4383 DE genes were obtained in IP24h and XP24h ovaries, respectively; top enriched terms were mostly associated with cell division and expansion in addition to the 'plant hormone signal transduction' pathway. These findings indicate that full penetration of pollen tubes can initiate fruit set and development independently of fertilization, most likely by activating the expression of genes regulating cell division and expansion.
PubMed: 37416886
DOI: 10.3389/fpls.2023.1205816 -
Plant & Cell Physiology May 2023In the anthers and ovaries of flowers, pollen grains and embryo sacs are produced with uniform cell compositions. This stable gametogenesis enables elaborate... (Review)
Review
In the anthers and ovaries of flowers, pollen grains and embryo sacs are produced with uniform cell compositions. This stable gametogenesis enables elaborate interactions between male and female gametophytes after pollination, forming the highly successful sexual reproduction system in flowering plants. As most ovules are fertilized with a single pollen tube, the resulting genome set in the embryo and endosperm is determined in a single pattern by independent fertilization of the egg cell and central cell by two sperm cells. However, if ovules receive four sperm cells from two pollen tubes, the expected options for genome sets in the developing seeds would more than double. In wild-type Arabidopsis thaliana plants, around 5% of ovules receive two pollen tubes. Recent studies have elucidated the abnormal fertilization in supernumerary pollen tubes and sperm cells related to polytubey, polyspermy, heterofertilization and fertilization recovery. Analyses of model plants have begun to uncover the mechanisms underlying this new pollen tube biology. Here, we review unusual fertilization phenomena and propose several breeding applications for flowering plants. These arguments contribute to the remodeling of plant reproduction, a challenging concept that alters typical plant fertilization by utilizing the current genetic toolbox.
Topics: Seeds; Arabidopsis; Pollen; Pollen Tube; Fertilization; Ovule; Reproduction
PubMed: 36943745
DOI: 10.1093/pcp/pcad021 -
Nature Communications May 2020Pollen tubes are highly polarized tip-growing cells that depend on cytosolic pH gradients for signaling and growth. Autoinhibited plasma membrane proton (H) ATPases...
Pollen tubes are highly polarized tip-growing cells that depend on cytosolic pH gradients for signaling and growth. Autoinhibited plasma membrane proton (H) ATPases (AHAs) have been proposed to energize pollen tube growth and underlie cell polarity, however, mechanistic evidence for this is lacking. Here we report that the combined loss of AHA6, AHA8, and AHA9 in Arabidopsis thaliana delays pollen germination and causes pollen tube growth defects, leading to drastically reduced fertility. Pollen tubes of aha mutants had reduced extracellular proton (H) and anion fluxes, reduced cytosolic pH, reduced tip-to-shank proton gradients, and defects in actin organization. Furthermore, mutant pollen tubes had less negative membrane potentials, substantiating a mechanistic role for AHAs in pollen tube growth through plasma membrane hyperpolarization. Our findings define AHAs as energy transducers that sustain the ionic circuit defining the spatial and temporal profiles of cytosolic pH, thereby controlling downstream pH-dependent mechanisms essential for pollen tube elongation, and thus plant fertility.
Topics: Arabidopsis; Arabidopsis Proteins; Cell Membrane; Cell Polarity; Cytosol; Gene Knockdown Techniques; Germination; Hydrogen-Ion Concentration; Membrane Potentials; Mutation; Plants, Genetically Modified; Pollen Tube; Pollination; Protein Isoforms; Proton-Translocating ATPases; Spatio-Temporal Analysis
PubMed: 32409656
DOI: 10.1038/s41467-020-16253-1 -
Methods in Molecular Biology (Clifton,... 2020Mutant phenotype observation is the most useful and important method to study which biological process a gene-of-interest is involved in. In flowering plants, excessive...
Mutant phenotype observation is the most useful and important method to study which biological process a gene-of-interest is involved in. In flowering plants, excessive pollen grains land and germinate on the stigma, then pollen tubes grow through the transmitting tract to reach the ovules, eventually enter the micropyle to complete double fertilization. First, for mutants whose homozygotes could not be obtained due to pollen tube defects, it is difficult to observe the defect phenotype since the pollen grains of different genotypes are mixed together. Here, we provide a detailed protocol to pick out mutant pollen grains from the heterozygous mutant plants in Arabidopsis thaliana. By using this method, we could obtain sufficient mutant pollen grains for phenotypic analysis. Second, it is difficult to compare the pollen/pollen tube behavior of two different genotypes/species in vivo in a same pistil. Here, we develop a new dual staining method which combines GUS staining with aniline blue staining. By using this method, we can analyze the competence of the two different pollen tubes in the same pistil.
Topics: Arabidopsis; Cell Separation; Genetic Techniques; Microscopy, Fluorescence; Mutation; Phenotype; Pollen Tube; Staining and Labeling; Transgenes
PubMed: 32529436
DOI: 10.1007/978-1-0716-0672-8_12