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Vernonica E Franklintong - One of the best experts on this subject based on the ideXlab platform.
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the Papaver Rhoeas s determinants confer self incompatibility to arabidopsis thaliana in planta
Science, 2015Co-Authors: Deborah J Eaves, Eugenio Sanchezmoran, Christopher F H Franklin, Vernonica E FranklintongAbstract:Self-incompatibility (SI) is a major genetically controlled system used to prevent inbreeding in higher plants. S determinants regulate allele-specific rejection of “self” pollen by the pistil. SI is an important model system for cell-to-cell recognition and signaling and could be potentially useful for first-generation (F1) hybrid breeding. To date, the transfer of S determinants has used the complementation of orthologs to “restore” SI in close relatives. We expressed the Papaver Rhoeas S determinants PrsS and PrpS in Arabidopsis thaliana. This enabled pistils to reject pollen expressing cognate PrpS. Moreover, plants coexpressing cognate PrpS and PrsS exhibit robust SI. This demonstrates that PrsS and PrpS are sufficient for a functional synthetic S locus in vivo. This transfer of novel S determinants into a highly divergent species (>140 million years apart) with no orthologs suggests their potential utility in crop production.
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Papaver Rhoeas s determinants and the signaling networks they trigger
2014Co-Authors: Vernonica E FranklintongAbstract:Higher plants use specific interactions between pollen and pistil to achieve pollination. Self-incompatibility (SI) is an important mechanism used by many species to prevent inbreeding. It is controlled by a multi-allelic S locus. “Self” (incompatible) pollen is discriminated from “non-self” (compatible) pollen by interaction of pollen and pistil S locus components and is subsequently inhibited. Our studies of the SI system in Papaver Rhoeas have revealed that the pistil S locus protein, PrsS, is a small novel secreted protein that interacts with the pollen S locus protein, PrpS, which is a small novel transmembrane protein. This interaction of PrsS with incompatible pollen induces a SI response, involving a Ca2+-dependent signaling network, resulting in pollen inhibition and programmed cell death; this provides a neat way to destroy “self”-pollen. Several SI-induced events have been identified, including Ca2+ and K+ influx, increases in cytosolic free Ca2+, activation of a MAP kinase, alterations to the cytoskeleton, and phosphorylation of a soluble inorganic pyrophosphatase. Here we present an overview of our knowledge of the novel cell–cell recognition S-determinants and the signals, targets, and mechanisms triggered by an incompatible interaction. We hope this review is of interest to those involved in the origins and evolution of cell–cell recognition systems involved in discrimination between “self” and “non-self,” which include histocompatibility systems in primitive chordates and vertebrates as well as plant self-incompatibility.
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self incompatibility in Papaver Rhoeas activates nonspecific cation conductance permeable to ca2 and k
Plant Physiology, 2011Co-Authors: Su Wang, Shaoling Zhang, Stephen J Publicover, Vernonica E FranklintongAbstract:Cellular responses rely on signaling. In plant cells, cytosolic free calcium is a major second messenger, and ion channels play a key role in mediating physiological responses. Self-incompatibility (SI) is an important genetically controlled mechanism to prevent self-fertilization. It uses interaction of matching S-determinants from the pistil and pollen to allow “self” recognition, which triggers rejection of incompatible pollen. In Papaver Rhoeas, the S-determinants are PrsS and PrpS. PrsS is a small novel cysteine-rich protein; PrpS is a small novel transmembrane protein. Interaction of PrsS with incompatible pollen stimulates S-specific increases in cytosolic free calcium and alterations in the actin cytoskeleton, resulting in programmed cell death in incompatible but not compatible pollen. Here, we have used whole-cell patch clamping of pollen protoplasts to show that PrsS stimulates SI-specific activation of pollen grain plasma membrane conductance in incompatible but not compatible pollen grain protoplasts. The SI-activated conductance does not require voltage activation, but it is voltage sensitive. It is permeable to divalent cations (Ba2+ ≥ Ca2+ > Mg2+) and the monovalent ions K+ and NH4+ and is enhanced at voltages negative to −100 mV. The Ca2+ conductance is blocked by La3+ but not by verapamil; the K+ currents are tetraethylammonium chloride insensitive and do not require Ca2+. We propose that the SI-stimulated conductance may represent a nonspecific cation channel or possibly two conductances, permeable to monovalent and divalent cations. Our data provide insights into signal-response coupling involving a biologically important response. PrsS provides a rare example of a protein triggering alterations in ion channel activity.
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self incompatibility in Papaver Rhoeas progress in understanding mechanisms involved in regulating self incompatibility in Papaver
2008Co-Authors: Vernonica E FranklintongAbstract:Over the last 20 years or so, our knowledge of what is involved in the rejection of ‘self’ pollen in Papaver Rhoeas has expanded tremendously. From initial studies of the population genetics of the S-locus polymorphism, and identification of the pistil S-determinant, the focus has moved to elucidating the signals and mechanisms involved in mediating the inhibition of incompatible pollen tube growth. A key finding was the involvement of a Ca2+-dependent signalling network. This led to the discovery of several SI-induced events, including depolymerisation of the actin cytoskeleton and phosphorylation of a soluble inorganic pyrophosphatase, Prp26.1, which are involved in the rapid inhibition of pollen tube growth. Programmed cell death is also triggered; this provides a neat way to destroy self pollen. Recent studies have begun to unravel components involved in this important event, involving activation of several caspase-like activities. Here we review some of the key findings in recent years.
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genomic organization of the Papaver Rhoeas self incompatibility s1 locus
Journal of Experimental Botany, 2003Co-Authors: Michael J Wheeler, Vernonica E Franklintong, S A Armstrong, F C H FranklinAbstract:The self-incompatibility (SI) response in Papaver Rhoeas depends upon the cognate interaction between a pollen-expressed receptor and a stigmatically expressed ligand. The genes encoding these components are situated within the S-locus. In order for SI to be maintained, the genes encoded by the S-locus must be co-inherited with no recombination between them. Several hypotheses, including sequence heterogeneity and chromosomal position, have been put forward to explain the maintenance of the S-locus in the SI systems of the Brassicaceae and the Solanaceae. A region of the Papaver Rhoeas genome encompassing part of the self-incompatibility S(1) locus has been cloned and sequenced. The clone contains the gene encoding the stigmatic component of the response, but does not contain a putative pollen S-gene. The sequence surrounding the S(1) gene contains several diverse repetitive DNA elements. As such, the P. Rhoeas S-locus bears similarities to the S-loci of other SI systems. An attempt to localize the P. Rhoeas S-locus using fluorescence in situ hybridization (FISH) has also been made. The potential relevance of the findings to mechanisms of recombination suppression is discussed.
M J Lawrence - One of the best experts on this subject based on the ideXlab platform.
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the population genetics of the self incompatibility polymorphism in Papaver Rhoeas xi the effects of limited pollen and seed dispersal overlapping generations and variation in plant size on the variance of s allele frequencies in populations at equilibrium
Heredity, 1996Co-Authors: Roger J Brooks, Andrew M Tobias, M J LawrenceAbstract:The population genetics of the self-incompatibility polymorphism in Papaver Rhoeas . XI. The effects of limited pollen and seed dispersal, overlapping generations and variation in plant size on the variance of S-allele frequencies in populations at equilibrium
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Genetics of seed dormancy in Papaver Rhoeas
Heredity, 1995Co-Authors: M D Lane, M J LawrenceAbstract:Seed dormancy in a cross between wild Papaver Rhoeas and its ‘Shirley’ cultivar appeared to be controlled by genes that displayed additive effects, dominance in the direction of low dormancy and non-allelic interaction of the duplicate type; in addition, there was a small maternal dominance effect in the direction of high dormancy. The genetics of seed dormancy in this cross is as predicted on Mather's theory of genetical architecture for a character that has been subject to strong directional selection. During the breeding of 'Shirley' poppies, at least six flower colour mutations were obtained in less than 20 years in a population whose effective size must have been very small. It is argued that, in view of the difficulty of detecting heritable variation for seed dormancy in wild poppies and the rarity of flower colour variants in wild P. Rhoeas, it is possible that seed of the ‘Shirley’ cultivar lacks the dormancy of its wild ancestors because of mutation of one or two genes.
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the population genetics of the self incompatibility polymorphism in Papaver Rhoeas x an association between incompatibility genotype and seed dormancy
Heredity, 1995Co-Authors: M D Lane, M J LawrenceAbstract:The population genetics of the self-incompatibility polymorphism in Papaver Rhoeas . X. An association between incompatibility genotype and seed dormancy
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cloning and expression of a distinctive class of self incompatibility s gene from Papaver Rhoeas l
Proceedings of the National Academy of Sciences of the United States of America, 1994Co-Authors: H C Foote, M J Lawrence, Vernonica E Franklintong, Jon P Ride, E A Walker, F C H FranklinAbstract:We present the identification, cloning, and characterization of a self-incompatibility (S) gene from Papaver Rhoeas that has no significant homology to any previously reported gene sequences, including S genes from other species. This result suggests that a different self-incompatibility mechanism may be operating in this species and has important implications for the evolutionary relationships between the S genes. The S1 cDNA was cloned by using an oligonucleotide based upon N-terminal amino acid sequence data from stigmatic proteins that show complete linkage with the S1 gene. The single-copy gene has been expressed in Escherichia coli to test biological activity. Although the recombinant S1 protein (S1e) is not processed in the same way as the protein produced in the plant, it exhibits, in vitro, the specific pollen inhibitory activity expected of an S gene product; pollen carrying the S1 allele is inhibited, whereas pollen not carrying S1 is not inhibited. These results provide definitive demonstration that the product of a cloned S gene has S-specific pollen inhibitory activity.
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the population genetics of the self incompatibility polymorphism in Papaver Rhoeas vii the number of s alleles in the species
Heredity, 1993Co-Authors: M D Lane, M J LawrenceAbstract:The population genetics of the self-incompatibility polymorphism in Papaver Rhoeas . VII. The number of S-alleles in the species
F C H Franklin - One of the best experts on this subject based on the ideXlab platform.
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genomic organization of the Papaver Rhoeas self incompatibility s1 locus
Journal of Experimental Botany, 2003Co-Authors: Michael J Wheeler, Vernonica E Franklintong, S A Armstrong, F C H FranklinAbstract:The self-incompatibility (SI) response in Papaver Rhoeas depends upon the cognate interaction between a pollen-expressed receptor and a stigmatically expressed ligand. The genes encoding these components are situated within the S-locus. In order for SI to be maintained, the genes encoded by the S-locus must be co-inherited with no recombination between them. Several hypotheses, including sequence heterogeneity and chromosomal position, have been put forward to explain the maintenance of the S-locus in the SI systems of the Brassicaceae and the Solanaceae. A region of the Papaver Rhoeas genome encompassing part of the self-incompatibility S(1) locus has been cloned and sequenced. The clone contains the gene encoding the stigmatic component of the response, but does not contain a putative pollen S-gene. The sequence surrounding the S(1) gene contains several diverse repetitive DNA elements. As such, the P. Rhoeas S-locus bears similarities to the S-loci of other SI systems. An attempt to localize the P. Rhoeas S-locus using fluorescence in situ hybridization (FISH) has also been made. The potential relevance of the findings to mechanisms of recombination suppression is discussed.
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evidence for dna fragmentation triggered in the self incompatibility response in pollen of Papaver Rhoeas
Plant Journal, 2000Co-Authors: N D Jordan, F C H Franklin, Vernonica E FranklintongAbstract:Summary Studies of the molecular and biochemical basis of self-incompatibility (SI) in Papaver Rhoeas have revealed much about the signalling pathways triggered in pollen early in this response. The aim of the current investigation was to begin to study downstream events in order to elucidate some of the later cellular responses involved in the SI response and identification of the mechanisms controlling the irreversible inhibition of pollen tube growth. We have used the FragEL assay to investigate if there is any evidence for DNA fragmentation stimulated in pollen of P. Rhoeas in an S-specific manner. Our data clearly demonstrate that S proteins are responsible for triggering this, specifically in incompatible, and not compatible, pollen. DNA fragmentation was first detected in incompatible pollen tubes 4 h after challenge with S proteins, and continued to increase for a further 10 h. This provides the first evidence, to our knowledge, that this phenomenon is associated with the SI response. We also demonstrate that mastoparan, which increases [Ca2+]i, also triggers DNA fragmentation in these pollen tubes, thereby implicating an involvement of Ca2+ signalling in this process. Together, our data represent a significant breakthrough in understanding of the SI response in Papaver pollen.
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s protein mutants indicate a functional role for sbp in the self incompatibility reaction of Papaver Rhoeas
Plant Journal, 1999Co-Authors: N D Jordan, Vernonica E Franklintong, Jon P Ride, K Kakeda, Alex C Conner, F C H FranklinAbstract:The self-incompatibility response involves S-allele specific recognition between stigmatic S proteins and incompatible pollen, resulting in S-specific pollen inhibition. In Papaver Rhoeas, the pollen S gene product is predicted to be a receptor that interacts with the stigmatic S protein in an S specific manner. We recently identified an S protein binding protein (SBP) in pollen that binds stigmatic S proteins, although apparently not in an S-allele-specific manner. In order to investigate the functional significance of the interaction between S proteins and SBP, we constructed mutant derivatives of the S1 protein and tested their SBP-binding activity and their biological activity. Here we present an evaluation of nine mutant derivatives of the S1 protein. Western ligand blotting was used to show that mutations to amino acid residues in predicted loops 2 and 6 of the S1 protein cause significant reductions in their SBP-binding activity. These same mutants show a concomitant reduction in their ability to inhibit incompatible pollen. This establishes a direct link between SBP binding and inhibition of incompatible pollen and implicates SBP as a pollen component playing a key role in the self-incompatibility reaction. We discuss the possible nature of the contribution of SBP in the S-specific rejection of incompatible pollen.
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Second-messenger-induced signalling events in pollen tubes of Papaver Rhoeas
Experimental Biology Online, 1997Co-Authors: B. K. Dr⊘bak, F C H Franklin, P. J. Shaw, G. M. Calder, A. J. Trewavas, A. C. Allan, V E Franklin-tongAbstract:A role for cytosolic free Ca^2+ (Ca^2+_i) in the regulation of growth of Papaver Rhoeas pollen tubes during the self-incompatibility response has recently been demonstrated [Franklin-Tong et al. Plant J. 4 :163–177 (1993); Franklin-Tong et al. Plant J. 8 :299–307 (1995); Franklin-Tong et al. submitted to Plant J .]. We have investigated the possibility that Ca^2+_i is more generally involved in the regulation of pollen tube growth using confocal laser scanning microscopy (CLSM). Data obtained using Ca^2+ imaging, in conjunction with photolytic release of caged inositol 1,4,5-trisphosphate [Ins(1,4,5) P _3], point to a central role of the phosphoinositide signal transduction pathway in the control of Ca^2+ fluxes and control of pollen tube growth. These experiments further revealed that increases in cytosolic levels of Ins(1,4,5) P _3 resulted in the formation of distinct Ca^2+ waves. Experiments using the pharmacological agents heparin, neomycin and mastoparan further indicated that Ca^2+ waves are propagated, at least in part, by Ins(1,4,5) P _3-induced Ca^2+ release rather than by simple diffusion or by “classic” Ca^2+-induced Ca^2+ release mechanisms. We also have data which suggest that Ca^2+ waves and oscillations may be induced by photolytic release of caged Ca^2+. Ratio-imaging has enabled us to identify an apical oscillating Ca^2+ gradient in growing pollen tubes, which may regulate normal pollen tube growth. We also present evidence for the involvement of Ca^2+ waves in mediating the self-incompatibility response. Our data suggest that changes in Ca^2+_i and alterations in growth rate/patterns are likely to be closely correlated and may be causally linked to events such as Ca^2+-induced, or Ins(1,4,5) P _3-induced wave formation and apical Ca^2+ oscillations.
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increased phosphorylation of a 26 kd pollen protein is induced by the self incompatibility response in Papaver Rhoeas
The Plant Cell, 1996Co-Authors: J J Rudd, F C H Franklin, Janet M Lord, Vernonica E FranklintongAbstract:We have investigated whether specific protein phosphorylation events are induced in Papaver Rhoeas pollen as a consequence of the self-incompatibility (SI) response. Pollen grown in vitro in the presence of 32P-orthophosphate was challenged with biologically active recombinant S proteins, and pollen proteins were extracted and analyzed. The results provide strong evidence that the increased phosphorylation of a 26-kD protein of pl 6.2, p26, is specifically induced by the SI response. This phosphorylation event occurs in living pollen tubes and was observed specifically when pollen was challenged with S proteins that are incompatible with the S alleles carried by the pollen and not when pollen was challenged with compatible or incompatible heat-denatured S proteins. Further characterization demonstrated that p26 comprises two phosphoproteins, p26.1 and p26.2, that are found in soluble and microsomal fractions, respectively. Increased phosphorylation of p26.1 is implicated in the SI response and appears to be Ca2+ and calmodulin dependent. These data argue for the involvement of a Ca2+-dependent protein kinase requiring calmodulin-like domains, whose activation comprises an intracellular signal mediating the SI response in P. Rhoeas pollen.
Anja Geitmann - One of the best experts on this subject based on the ideXlab platform.
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The self-incompatibility response in Papaver Rhoeas pollen causes early and striking alterations to organelles
Cell Death & Differentiation, 2004Co-Authors: Anja Geitmann, V E Franklin-tong, Anne Mie C EmonsAbstract:Self-incompatibility (SI) in Papaver Rhoeas is accompanied by a cascade of signalling events that result in the rapid arrest and eventual death of the pollen tube. We have used rapid freeze fixation, freeze substitution and transmission electron microscopy to provide the first description of changes to pollen at the ultrastructural level during SI in this species. Our studies reveal that dramatic alterations to the morphology of mitochondria, Golgi bodies and ER occur within 1 h of SI induction. Similar symptoms have also been observed during programmed cell death (PCD) in some cell types. These include: the conspicuous condensation of the vegetative and generative nuclei, the swelling and loss of cristae in mitochondria and the disappearance of Golgi bodies. Some of the early alterations to the mitochondria and Golgi bodies observed at 1 h, almost certainly occur when cells are still alive. Other events, such as nuclear condensation, occur later and coincide with DNA fragmentation and the loss of cell viability. Our observations suggest that the SI response in P. Rhoeas pollen may potentially involve a type of PCD.
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alterations in the actin cytoskeleton of pollen tubes are induced by the self incompatibility reaction in Papaver Rhoeas
The Plant Cell, 2000Co-Authors: Anja Geitmann, Benjamin N Snowman, Anne Mie C Emons, Vernonica E FranklintongAbstract:Self-incompatibility (SI) is a genetically controlled process used to prevent self-pollination. In Papaver Rhoeas, the induction of SI is triggered by a Ca 2+ -dependent signaling pathway that results in the rapid and S allele–specific inhibition of pollen tube tip growth. Tip growth of cells is dependent on a functioning actin cytoskeleton. We have investigated the effect of self-incompatibility (S) proteins on the actin cytoskeleton in poppy pollen tubes. Here, we report that the actin cytoskeleton of incompatible pollen tubes is rapidly and dramatically rearranged during the SI response, not only in our in vitro SI system but also in vivo. We demonstrate that nonspecific inhibition of growth does not result in similar actin rearrangements. Because the SI-induced alterations are not observed if growth stops, this clearly demonstrates that these alterations are triggered by the SI signaling cascade rather than merely resulting from the consequent inhibition of growth. We establish a detailed time course of events and discuss the mechanisms that might be involved. Our data strongly implicate a role for the actin cytoskeleton as a target for signaling pathways involved in the SI response of P. Rhoeas .
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signalling and the cytoskeleton of pollen tubes of Papaver Rhoeas
Annals of Botany, 2000Co-Authors: Anja Geitmann, Benjamin N Snowman, Susan R Clarke, Christopher J StaigerAbstract:Self-incompatibility (SI) is a genetically controlled system used by many flowering plants to prevent self-pollination, often by the inhibition of pollen tube growth. The importance of cytosolic free calcium, [Ca2+]i, for the regulation of pollen tube growth is well known. We have established, using calcium imaging, that the SI response in Papaver Rhoeas L. pollen involves a calcium-mediated intracellular signalling pathway. Tip growth of cells is dependent upon a typical configuration of the actin cytoskeleton, which is controlled by actin binding proteins. In animal cells, the actin-binding protein, profilin, is thought to act as a key intermediate between signalling pathways and actin rearrangements. Profilin is an abundant component of pollen. To better understand the signalling cascades that modulate pollen tip growth and actin dynamics, we are investigating a possible signalling role for profilin. We have demonstrated that profilin modulates the phosphorylation of pollen proteins in vitro. This implicates a role for profilin in altering protein kinase or phosphatase activity. Furthermore, we demonstrate for the first time that profilin from pollen can be phosphorylated in vitro. This provides compelling evidence that profilin interacts with signalling pathways in angiosperms. Finally, we demonstrate that in the SI response, the actin cytoskeleton of incompatible pollen tubes is dramatically rearranged. Our data strongly support a role for the cytoskeleton and actin-binding proteins interacting with signalling pathways involved in the regulation of pollen tube growth.
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actin rearrangements in pollen tubes are stimulated by the self incompatibility si response in Papaver Rhoeas l
Actin: a dynamic framework for multiple plant cell functions, 2000Co-Authors: Benjamin N Snowman, Anja Geitmann, Anne Mie C Emons, Vernonica E FranklintongAbstract:Self-incompatibility (SI) is a genetically-controlled system used by many flowering plants to prevent self-fertilization. We have been investigating SI in Papaver Rhoeas for a number of years, and have begun to build up a picture of some of the signalling events and mechanisms involved in this specific inhibition of pollen tube growth. Pollen tubes elongate by tip growth, which is dependent upon the actin cytoskeleton, the structure of which is controlled by actin-binding proteins. To date, no studies, to our knowledge, have investigated the effect that a self-incompatible response may have on actin organisation in pollen tubes. Our investigations provide clear evidence that the actin cytoskeleton of incompatible pollen tubes undergoing SI is dramatically altered. These data strongly suggest that the actin cytoskeleton is targetted by the signalling pathway stimulated in the SI response. These findings may have implications for our understanding of regulation of pollen tube growth.
Christopher J Staiger - One of the best experts on this subject based on the ideXlab platform.
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A gelsolin-like protein from Papaver Rhoeas pollen (PrABP80) stimulates calcium-regulated severing and depolymerization of actin filaments
Journal of Biological Chemistry, 2004Co-Authors: Shanjin Huang, Laurent Blanchoin, Faisal Chaudhry, Vernonica E. Franklin-tong, Christopher J StaigerAbstract:The cytoskeleton is a key regulator of plant morphogenesis, sexual reproduction, and cellular responses to extracellular stimuli. During the self-incompatibility response of Papaver Rhoeas L. (field poppy) pollen, the actin filament network is rapidly depolymerized by a flood of cytosolic free Ca2+ that results in cessation of tip growth and prevention of fertilization. Attempts to model this dramatic cytoskeletal response with known pollen actin-binding proteins (ABPs) revealed that the major G-actin-binding protein profilin can account for only a small percentage of the measured depolymerization. We have identified an 80-kDa, Ca2+-regulated ABP from poppy pollen (PrABP80) and characterized its biochemical properties in vitro. Sequence determination by mass spectrometry revealed that PrABP80 is related to gelsolin and villin. The molecular weight, lack of filament cross-linking activity, and a potent severing activity are all consistent with PrABP80 being a plant gelsolin. Kinetic analysis of actin assembly/disassembly reactions revealed that substoichiometric amounts of PrABP80 can nucleate actin polymerization from monomers, block the assembly of profilin-actin complex onto actin filament ends, and enhance profilin-mediated actin depolymerization. Fluorescence microscopy of individual actin filaments provided compelling, direct evidence for filament severing and confirmed the actin nucleation and barbed end capping properties. This is the first direct evidence for a plant gelsolin and the first example of efficient severing by a plant ABP. We propose that PrABP80 functions at the center of the self-incompatibility response by creating new filament pointed ends for disassembly and by blocking barbed ends from profilin-actin assembly.
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the actin cytoskeleton is a target of the self incompatibility response in Papaver Rhoeas
Journal of Experimental Botany, 2003Co-Authors: Christopher J Staiger, Vernonica E FranklintongAbstract:The integration of signals received by a cell, and their transduction to targets, is essential for all cellular responses. The cytoskeleton has been identified as a major target of signalling cascades in both animal and plant cells. Self-incompatibility (SI) in Papaver Rhoeas involves an allele-specific recognition between stigmatic S-proteins and pollen, resulting in the inhibition of incompatible pollen. This highly specific response triggers a Ca 2+ -dependent signalling cascade in incompatible pollen when a stigmatic S-protein interacts with it. It has been demonstrated recently that SI induces dramatic alterations in the organization of the pollen actin cytoskeleton. This implicates the actin cytoskeleton as a key target for the SI-stimulated signals. The cytological alterations to the actin cytoskeleton that are triggered in response to SI are described here and there seem to be several stages that are distinguishable temporally. Evidence was obtained that F-actin depolymerization is also stimulated. The current understanding that the actin cytoskeleton is a target for the signals triggered by the SI response is discussed. It is suggested that these F-actin alterations may be Ca 2+ -mediated and that this could be a mechanism whereby SI-induced tip growth inhibition is achieved. The potential for actin-binding proteins to act as key mediators of this response is discussed and the mechanisms that may be responsible for effecting these changes are described. In particular, the parallels between sustained actin rearrangements during SI and in apoptosis of animal cells are considered.
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signalling and the cytoskeleton of pollen tubes of Papaver Rhoeas
Annals of Botany, 2000Co-Authors: Anja Geitmann, Benjamin N Snowman, Susan R Clarke, Christopher J StaigerAbstract:Self-incompatibility (SI) is a genetically controlled system used by many flowering plants to prevent self-pollination, often by the inhibition of pollen tube growth. The importance of cytosolic free calcium, [Ca2+]i, for the regulation of pollen tube growth is well known. We have established, using calcium imaging, that the SI response in Papaver Rhoeas L. pollen involves a calcium-mediated intracellular signalling pathway. Tip growth of cells is dependent upon a typical configuration of the actin cytoskeleton, which is controlled by actin binding proteins. In animal cells, the actin-binding protein, profilin, is thought to act as a key intermediate between signalling pathways and actin rearrangements. Profilin is an abundant component of pollen. To better understand the signalling cascades that modulate pollen tip growth and actin dynamics, we are investigating a possible signalling role for profilin. We have demonstrated that profilin modulates the phosphorylation of pollen proteins in vitro. This implicates a role for profilin in altering protein kinase or phosphatase activity. Furthermore, we demonstrate for the first time that profilin from pollen can be phosphorylated in vitro. This provides compelling evidence that profilin interacts with signalling pathways in angiosperms. Finally, we demonstrate that in the SI response, the actin cytoskeleton of incompatible pollen tubes is dramatically rearranged. Our data strongly support a role for the cytoskeleton and actin-binding proteins interacting with signalling pathways involved in the regulation of pollen tube growth.
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a potential signaling role for profilin in pollen of Papaver Rhoeas
The Plant Cell, 1998Co-Authors: Susan R Clarke, Christopher J Staiger, Bryan C Gibbon, Vernonica E FranklintongAbstract:Regulation of pollen tube growth is known to involve alterations in intracellular calcium levels and phosphoinositide signaling, although the mechanisms involved are unclear. However, it appears likely that pollination events involve a complex interplay between signaling pathways and components of the actin cytoskeleton in pollen. In many eukaryotic cells, actin binding proteins function as stimulus-response modulators, translating signals into alterations in the cytoplasmic architecture. In this study, we examined whether profilin, which is a member of this class of signaling intermediate, might play a similar role in pollen. We have analyzed the functional properties of native profilin from pollen of Papaver Rhoeas and have investigated the effects of profilin on the phosphorylation of pollen proteins in vitro by adding a slight excess of profilin to cytosolic pollen extracts. We present clear evidence that profilin interacts with soluble pollen components, resulting in dramatic alterations in the phosphorylation of several proteins. We also show, albeit in vitro, the involvement of profilin in modulating the activity of a signaling component(s) affecting protein phosphorylation. Our data, which suggest that pollen profilin can regulate actin-based cytoskeletal protein assembly and protein kinase or phosphatase activity, indicate a possible role for the involvement of profilin in signaling pathways that may regulate pollen tube growth.
