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Boisson-Dernier A, Frietsch S, Kim TH, Dizon MB, Schroeder JI. The peroxin loss-of-function mutation abstinence by mutual consent disrupts male-female gametophyte recognition. Curr Biol 2007; 18:63-8. [PMID: 18160292 DOI: 10.1016/j.cub.2007.11.067] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2007] [Revised: 11/12/2007] [Accepted: 11/27/2007] [Indexed: 11/28/2022]
Abstract
In eukaryotes, fertilization relies on complex and specialized mechanisms that achieve the precise delivery of the male gamete to the female gamete and their subsequent union [1-4]. In flowering plants, the haploid male gametophyte or pollen tube (PT) [5] carries two nonmotile sperm cells to the female gametophyte (FG) or embryo sac [6] during a long assisted journey through the maternal tissues [7-10]. In Arabidopsis, typically one PT reaches one of the two synergids of the FG (Figure 1A), where it terminates its growth and delivers the sperm cells, a poorly understood process called pollen-tube reception. Here, we report the isolation and characterization of the Arabidopsis mutant abstinence by mutual consent (amc). Interestingly, pollen-tube reception is impaired only when an amc pollen tube reaches an amc female gametophyte, resulting in pollen-tube overgrowth and completely preventing sperm discharge and the development of homozygous mutants. Moreover, we show that AMC is strongly and transiently expressed in both male and female gametophytes during fertilization and that AMC functions in gametophytes as a peroxin essential for protein import into peroxisomes. These findings show that peroxisomes play an unexpected key role in gametophyte recognition and implicate a diffusible signal emanating from either gametophyte that is required for pollen-tube discharge.
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Affiliation(s)
- Aurélien Boisson-Dernier
- Division of Biological Sciences, Cell and Developmental Biology Section and Center for Molecular Genetics, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0116, USA.
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53
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Abstract
Early embryonic development in the flowering plant Arabidopsis thaliana follows a predictable sequence of cell divisions. Anatomical hallmarks and the expression of marker genes in dynamic patterns indicate that new cell fates are established with virtually every round of mitosis. Although some of the factors regulating these early patterning events have been identified, the overall process remains relatively poorly understood. Starting at the globular stage, when the embryo has approximately 100 cells, the organization of development appears to be taken over by programs that regulate postembryonic patterning throughout the life cycle.
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Affiliation(s)
- Pablo D Jenik
- Carnegie Institution, Department of Plant Biology, Stanford University, Stanford, CA 94305, USA.
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54
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Kägi C, Gross-Hardt R. How females become complex: cell differentiation in the gametophyte. CURRENT OPINION IN PLANT BIOLOGY 2007; 10:633-8. [PMID: 17851110 DOI: 10.1016/j.pbi.2007.07.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2007] [Revised: 07/11/2007] [Accepted: 07/26/2007] [Indexed: 05/08/2023]
Abstract
In contrast to animals, gametes in plants form a separate haploid generation, the gametophyte. The female gametophyte of flowering plants consists of just four different cell types that play distinct roles in the reproductive process. Differentiation of the distinct cell fates is tightly controlled and appears to follow regional cues that are arranged along a polar axis. Mutant analysis suggests that important aspects of gametophyte patterning are gametophytically regulated. Additionally, structural and molecular changes following misspecification indicate that the female gametophyte is a remarkably versatile structure with enormous respecification potential. Recently, new tools have been developed that open fascinating possibilities to access and analyze those processes that ultimately ensure successful fertilization.
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Affiliation(s)
- Christina Kägi
- ZMBP Developmental Genetics, University of Tübingen, D-72076 Tübingen, Germany
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55
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Wilsen KL, Hepler PK. Sperm Delivery in Flowering Plants: The Control of Pollen Tube Growth. Bioscience 2007. [DOI: 10.1641/b571006] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
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56
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Chen YH, Li HJ, Shi DQ, Yuan L, Liu J, Sreenivasan R, Baskar R, Grossniklaus U, Yang WC. The central cell plays a critical role in pollen tube guidance in Arabidopsis. THE PLANT CELL 2007; 19:3563-77. [PMID: 18055609 PMCID: PMC2174880 DOI: 10.1105/tpc.107.053967] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2007] [Revised: 10/28/2007] [Accepted: 11/04/2007] [Indexed: 05/18/2023]
Abstract
The sperm cell of flowering plants cannot migrate unaided and must be transported by the pollen tube cell of the male gametophyte to achieve successful fertilization. Long-distance pollen tube guidance is controlled by the seven-celled female gametophyte, the embryo sac. Previous reports showed that the synergid cell of the embryo sac is essential for pollen tube guidance. Here, we report the identification of a central cell guidance (ccg) mutant, which is defective in micropylar pollen tube guidance. CCG encodes a nuclear protein with an N-terminal conserved zinc beta-ribbon domain that is functionally interchangeable with that of TFIIB in yeast. This suggests that CCG might act as a transcription regulator for pollen tube guidance. CCG is expressed in the central cell of the female gametophyte. Expression of CCG in the central cell alone is sufficient to restore the normal pollen tube guidance phenotype, demonstrating that the central cell plays a critical role in pollen tube guidance.
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Affiliation(s)
- Yan-Hong Chen
- Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
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57
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Gross-Hardt R, Kägi C, Baumann N, Moore JM, Baskar R, Gagliano WB, Jürgens G, Grossniklaus U. LACHESIS restricts gametic cell fate in the female gametophyte of Arabidopsis. PLoS Biol 2007; 5:e47. [PMID: 17326723 PMCID: PMC1804285 DOI: 10.1371/journal.pbio.0050047] [Citation(s) in RCA: 144] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2006] [Accepted: 12/14/2006] [Indexed: 01/07/2023] Open
Abstract
In flowering plants, the egg and sperm cells form within haploid gametophytes. The female gametophyte of Arabidopsis consists of two gametic cells, the egg cell and the central cell, which are flanked by five accessory cells. Both gametic and accessory cells are vital for fertilization; however, the mechanisms that underlie the formation of accessory versus gametic cell fate are unknown. In a screen for regulators of egg cell fate, we isolated the lachesis (lis) mutant which forms supernumerary egg cells. In lis mutants, accessory cells differentiate gametic cell fate, indicating that LIS is involved in a mechanism that prevents accessory cells from adopting gametic cell fate. The temporal and spatial pattern of LIS expression suggests that this mechanism is generated in gametic cells. LIS is homologous to the yeast splicing factor PRP4, indicating that components of the splice apparatus participate in cell fate decisions. The selection and specification of the egg cell determine the number of eggs produced by an animal or plant, which in turn dictates how many offspring that organism can produce. In most higher plants, the egg cell forms in a specialized structure consisting of four different cell types. Two cells, the egg cell and the central cell, are fertilized by sperm cells and develop into the embryo proper and the nutritive tissue (endosperm), respectively. These two gametic cells are flanked by accessory cells; but why do some cells become gametic while others differentiate into accessory cells? To answer this question, we looked for mutants in which this process is disturbed. In the lachesis mutant, accessory cells become extra egg cells. Interestingly, it seems that the misspecification of these accessory cells results from defects in the gametic cells. This suggests that accessory cells monitor the state of the gametic cells to act as a backup if required, ensuring the formation of the key reproductive cells. In plant egg cells, gametophytes differentiate into both gametic and accessory cells; here the authors characterize a mutant that turns accessory cells into gametic cells.
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Affiliation(s)
- Rita Gross-Hardt
- Institute of Plant Biology and Zürich-Basel Plant Science Center, University of Zürich, Zürich, Switzerland.
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58
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Punwani JA, Rabiger DS, Drews GN. MYB98 positively regulates a battery of synergid-expressed genes encoding filiform apparatus localized proteins. THE PLANT CELL 2007; 19:2557-68. [PMID: 17693534 PMCID: PMC2002610 DOI: 10.1105/tpc.107.052076] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
The synergid cells within the female gametophyte are essential for reproduction in angiosperms. MYB98 encodes an R2R3-MYB protein required for pollen tube guidance and filiform apparatus formation by the synergid cells. To test the predicted function of MYB98 as a transcriptional regulator, we determined its subcellular localization and examined its DNA binding properties. We show that MYB98 binds to a specific DNA sequence (TAAC) and that a MYB98-green fluorescent protein fusion protein localizes to the nucleus, consistent with a role in transcriptional regulation. To identify genes regulated by MYB98, we tested previously identified synergid-expressed genes for reduced expression in myb98 female gametophytes and identified 16 such genes. We dissected the promoter of one of the downstream genes, DD11, and show that it contains a MYB98 binding site required for synergid expression, suggesting that DD11 is regulated directly by MYB98. To gain insight into the functions of the downstream genes, we chose five genes and determined the subcellular localization of the encoded proteins. We show that these five proteins are secreted into the filiform apparatus, suggesting that they play a role in either the formation or the function of this unique structure. Together, these data suggest that MYB98 functions as a transcriptional regulator in the synergid cells and activates the expression of genes required for pollen tube guidance and filiform apparatus formation.
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Affiliation(s)
- Jayson A Punwani
- Department of Biology, University of Utah, Salt Lake City, Utah 84112-0840, USA
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59
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Ranganath RM. Asymmetric cell division--how flowering plant cells get their unique identity. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 2007; 45:39-60. [PMID: 17585495 DOI: 10.1007/978-3-540-69161-7_2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
A central question in biology is how cell fate is specified during development of a multicellular organism. Flowering plants use two major pathways of asymmetric cell divisions in a spatio-temporal manner to achieve required cellular differentiation. In the 'one mother--two different daughters' pathway, a mother cell mitotically divides to produce two daughter cells of different size and fate. By contrast, the 'coenocyte-cellularization' pathway involves formation of a coenocyte, nuclear migration to specific locations of the coenocyte and cellularization of these nuclei by unique wall forming processes. Given that cell fate determinants play a key role in establishing cell identity, their allocation to daughter cells in the two pathways needs to be understood in terms of the unique cell cycle regulatory mechanisms involved. Most of the information available on cell fate determination in flowering plants is in the form of genes identified from mutant analysis. Novel techniques of interrogating individual plant cells in vivo are necessary to advance the extant knowledge from genetics to functional genomics data bases.
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Affiliation(s)
- R M Ranganath
- Department of Botany, Bangalore University, Jnanabharathi Campus, Bangalore 560056, India.
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60
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Ingouff M, Hamamura Y, Gourgues M, Higashiyama T, Berger F. Distinct dynamics of HISTONE3 variants between the two fertilization products in plants. Curr Biol 2007; 17:1032-7. [PMID: 17555967 DOI: 10.1016/j.cub.2007.05.019] [Citation(s) in RCA: 193] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2007] [Revised: 04/19/2007] [Accepted: 05/07/2007] [Indexed: 11/15/2022]
Abstract
Sexual reproduction involves epigenetic reprogramming comprising DNA methylation and histone modifications. In addition, dynamics of HISTONE3 (H3) variant H3.3 upon fertilization are conserved in animals, suggesting an essential role. In contrast to H3, H3.3 marks actively transcribed regions of the genome and can be deposited in a replication-independent manner. Although H3 variants are conserved in plants, their dynamics during fertilization have remained unexplored. We overcame technical limitations to live imaging of the fertilization process in Arabidopsis thaliana and studied dynamics of the male-gamete-specific H3.3 and the centromeric Histone Three Related 12 (HTR12). The double-fertilization process in plants produces the zygote and the embryo-nourishing endosperm. We show that the zygote is characterized by replication-independent removal of paternal H3.3 and homogeneous incorporation of parental chromatin complements. In the endosperm, the paternal H3.3 is passively diluted by replication while the paternal chromatin remains segregated apart from the maternal chromatin (gonomery). Hence epigenetic regulations distinguish the two products of fertilization in plants. H3.3-replication-independent dynamics and gonomery also mark the first zygotic divisions in animal species. We thus propose the convergent selection of parental epigenetic imbalance involving H3 variants in sexually reproducing organisms.
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Affiliation(s)
- Mathieu Ingouff
- Chromatin and Reproduction group, Temasek Life Sciences Laboratory, National University of Singapore, 1 Research link, 117604 Singapore, Republic of Singapore
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61
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Hiscock SJ, Bright J, McInnis SM, Desikan R, Hancock JT. Signaling on the Stigma: Potential New Roles for ROS and NO in Plant Cell Signaling. PLANT SIGNALING & BEHAVIOR 2007; 2:23-4. [PMID: 19704802 PMCID: PMC2633892 DOI: 10.4161/psb.2.1.3644] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2006] [Accepted: 12/01/2006] [Indexed: 05/19/2023]
Abstract
Reactive oxygen species (ROS) and reactive nitrogen species, particularly NO, are key components of diverse signaling networks in animals and plants. We have recently shown that epidermal cells of stigmas from a range of different angiosperms accumulate relatively large amounts of ROS, principally H(2)O(2), whereas pollen produces NO. Importantly, ROS/H(2)O(2) levels appeared reduced in stigma cells supporting developing pollen grains compared to cells without pollen grains attached. To explore a possible link between pollen NO production and reduced levels of stigmatic ROS/H(2)O(2), we supplied stigmas with NO and observed an overall reduction in levels of stigmatic ROS/H(2)O(2). These new and unexpected data suggest a potential new signaling role for ROS/H(2)O(2) and NO in pollen-stigma recognition processes.
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Affiliation(s)
- Simon J Hiscock
- School of Biological Sciences, University of Bristol; Bristol UK
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62
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Berger F, Grini PE, Schnittger A. Endosperm: an integrator of seed growth and development. CURRENT OPINION IN PLANT BIOLOGY 2006; 9:664-70. [PMID: 17011228 DOI: 10.1016/j.pbi.2006.09.015] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2006] [Accepted: 09/20/2006] [Indexed: 05/08/2023]
Abstract
Plant reproduction relies on interactions between parental and zygotic components. Elaborate reciprocal signaling pathways enable coordination of the genetic programs between these components. A first and important step in this communication is the tight control of cell cycle events in the gametes prior to fertilization. This prepares for coordinated fertilization and the initiation of seed development. The dialog between the various actors of reproduction extends after fertilization, with the endosperm taking a central role. Importantly, the endosperm mediates a maternal input that is based on memory of the transcriptional states of imprinted genes, which is crucial for harmonious seed growth. Our current knowledge suggests that the endosperm is an integrator of the different components and genetic programs that are involved in seed development.
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Affiliation(s)
- Frédéric Berger
- Temasek Lifescience Laboratory, 1 Research Link, National University of Singapore, 117604, Singapore.
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63
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Cole RA, Fowler JE. Polarized growth: maintaining focus on the tip. CURRENT OPINION IN PLANT BIOLOGY 2006; 9:579-88. [PMID: 17010659 DOI: 10.1016/j.pbi.2006.09.014] [Citation(s) in RCA: 176] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2006] [Accepted: 09/19/2006] [Indexed: 05/04/2023]
Abstract
Tip growth, a spatially focused cell expansion, has been best characterized in two plant cell types: pollen tubes and root hairs. It has long been established that both cell types require three intracellular components for this process: a tip-high calcium gradient, a polarized actin cytoskeleton, and tip-directed vesicle trafficking. More recently, additional mechanistic parallels have been observed between the two cell types, including roles for ROP and Rab GTPase signaling, phosphoinositides, calcium-dependent protein kinases, and the exocyst. Uncovering pathways that control the three components is beginning to reveal a highly interconnected network, which we call the tip growth LENS (for localization enhancing network, self-sustaining), that coordinates the required cellular activities to allow regulated tip growth, and to maintain itself as the tip advances.
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Affiliation(s)
- Rex A Cole
- Molecular and Cellular Biology Program, Oregon State University, Corvallis, Oregon 97331, USA
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64
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McInnis SM, Desikan R, Hancock JT, Hiscock SJ. Production of reactive oxygen species and reactive nitrogen species by angiosperm stigmas and pollen: potential signalling crosstalk? THE NEW PHYTOLOGIST 2006; 172:221-8. [PMID: 16995910 DOI: 10.1111/j.1469-8137.2006.01875.x] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Angiosperm stigmas exhibit high levels of peroxidase activity when receptive to pollen. To explore possible function(s) of this peroxidase activity we investigated amounts of reactive oxygen species (ROS), particularly hydrogen peroxide, in stigmas and pollen. Because nitric oxide (NO) was recently implicated in pollen tube growth, we also investigated amounts of NO in pollen and stigmas. Reactive oxygen species accumulation was assessed with confocal microscopy and light microscopy using ROS probes DCFH2-DA and TMB, respectively. NO was assayed using the NO probe DAF-2DA and confocal microscopy. Stigmas from various different angiosperms were found to accumulate ROS, predominantly H2O2, constitutively. In Senecio squalidus and Arabidopsis thaliana high amounts of ROS/H2O2 were localized to stigmatic papillae. ROS/H2O2 amounts appeared reduced in stigmatic papillae to which pollen grains had adhered. S. squalidus and A. thaliana pollen produced relatively high amounts of NO compared with stigmas; treating stigmas with NO resulted in reduced amounts of stigmatic ROS/H2O2. Constitutive accumulation of ROS/H2O2 appears to be a feature of angiosperm stigmas. This novel finding is discussed in terms of a possible role for stigmatic ROS/H2O2 and pollen-derived NO in pollen-stigma interactions and defence.
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Affiliation(s)
- Stephanie M McInnis
- School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK
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