Academic literature on the topic 'Interactions pollen–pistil'

The pollen tube represents an attractive model system for functional genomic analysis of the cell–cell interactions that mediate guided cellular growth. The pollen tube extends through pistil tissues and responds to guidance cues that direct the tube towards an ovule, where it releases sperm for fertilization. Pollen is readily isolated from anthers, where it is produced, and can be induced to produce a tube in vitro. Interestingly, pollen tube growth is significantly enhanced in pistils, and pollen tubes are rendered competent to respond to guidance cues after growth in a pistil. This potentiation of the pollen tube by the pistil suggested that pollen tubes alter their gene-expression programme in response to their environment. Recently, the transcriptomes of pollen tubes grown in vitro or through pistil tissues were determined. Significant changes in the transcriptome were found to accompany growth in vitro and through the pistil tissues. Reverse genetic analysis of pollen-tube-induced genes identified a new set of factors critical for pollen tube extension and navigation of the pistil environment. Recent advances reviewed in the present paper suggest that functional genomic analysis of pollen tubes has the potential to uncover the regulatory networks that shape the genetic architecture of the pollen tube as it responds to migratory cues produced by the pistil.

A developmental analysis of pollination responses in Arabidopsis implicates pollen as well as stigma maturation factors in the acquisition of reproductive function. In the anther, competence of pollen to germinate and to produce pollen tubes in situ occurred late in development. In the pistil, competence to support pollen germination and tube growth extended over a broad developmental window, and abundant as well as efficient pollen tube development was observed on pistils at anthesis and for a period of 1–2 days prior to flower opening. In contrast, pollen tube growth on immature pistils was found to proceed at low efficiency, at reduced growth rates, and with lack of directionality. Based on the pattern of pollen tube growth at different stages of pistil maturation, temporally regulated signals emanating from specialized cells of the pistil are inferred to be operative in each of the four identified phases of pollen tube growth. In the stigma and the stylar transmitting tissue, these signals directed the path of intra-specific pollen tubes as well as pollen tubes from another cruciferous genera, Brassica. By contrast, in the ovary, signaling by the ovule was effective only on intra-specific pollen tubes and was thus identified as the basis of inter-specific incompatibility. Furthermore, the acquisition of reproductive function was found to involve, in addition to the induction of a variety of stimulatory signals, a heretofore unrecognized developmental restriction in the capacity of epidermal surfaces of the flower to support pollen tube growth.

Pollen-pistil interactions serve as important prezygotic reproductive barriers that play a critical role in mate selection in plants. Here, we highlight recent progress toward understanding the molecular basis of pollen-pistil interactions as reproductive isolating barriers. These barriers can be active systems of pollen rejection, or they can result from a mismatch of required male and female factors. In some cases, the barriers are mechanistically linked to self-incompatibility systems, while others represent completely independent processes. Pollen-pistil reproductive barriers can act as soon as pollen is deposited on a stigma, where penetration of heterospecific pollen tubes is blocked by the stigma papillae. As pollen tubes extend, the female transmitting tissue can selectively limit growth by producing cell wall–modifying enzymes and cytotoxins that interact with the growing pollen tube. At ovules, differential pollen tube attraction and inhibition of sperm cell release can act as barriers to heterospecific pollen tubes.

Thesis (Ph. D.)--University of Missouri-Columbia, 2008.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 4, 2009) Vita. Includes bibliographical references.

Understanding the complex cellular courtship that occurs between the pollen and pistil tissues of flowering plants is a major goal for plant scientists. These pollen pistil interactions are characterised by a diverse range of molecules and processes, and many alternative mechanisms are employed by different species both to achieve successful pollination and to reject incompatible pollen. Due to their diverse nature, relatively little is known about these processes, and a general lack of consensus between taxa has been observed. The most well-studied of these processes are the self-incompatibility (SI) systems which act to recognise and reject self-pollen.

Pequenos peptídeos são importantes sinalizadores celulares e estão envolvidos na comunicação célula-a-célula em diversos aspectos do desenvolvimento da planta. Durante a reprodução sexual, moléculas sinalizadoras atuam na interação entre o gametófito feminino e o masculino, controlando processos como germinação do grão de pólen, alongamento do tubo polínico e liberação das células espermáticas, entre outros. RALF é um peptídeo de sinalização codificado por genes de expressão ubíqua ou tecido-especifica e que regulam negativamente a expansão celular. Em arabidopsis, peptídeos AtRALFs podem ser agrupados em uma família de 39 membros e, interessantemente, os maiores níveis de expressão gênica dessa família são encontrados nos AtRALFs expressos em tecidos reprodutivos.
Small peptides are important cell signaling involved in several aspects of plant development. During sexual reproduction, signaling molecules act in the interaction between female and male gametophyte, controlling processes such as pollen grains germination, pollen tube elongation and sperm cells release. RALF is a signaling peptide ubiquitous or tissuespecific that negatively regulates cell growth. In arabidopsis, AtRALFs peptides can be grouped into a family of 39 members and, interestingly, the highest levels of gene expression of this family are found in AtRALFs expressed in reproductive tissues.

Rac/Rop GTPases are molecular switches in plants that control the growth of polarized cells such as pollen tubes and root hairs, differentiation, development, actin dynamics, production of reactive oxygen species (ROS) and disease resistance. These small GTPases are activated by guanine nucleotide exchange factors (GEFs) that replace GDP for GTP and are referred to as RopGEFs in plants. To identify upstream components of the RopGEF regulated signaling pathways, GEF1 from Arabidopsis thaliana was used as a bait to screen a seedling cDNA library in a yeast two-hybrid system. This yielded members of a small family of the Catharanthus roseus Receptor-like kinase (CrRLK), referred to as the Feronia-like Receptor-like kinase (FlRLK) family as the potential GEF interactors. A synergid cell-expressed member of this family, FERONIA/SIRENE (RLK-10), regulates pollen tube reception by the female gametophyte and along with the other two plasma-membrane bound receptors of this family, THESEUS (RLK-3) and HERCULES (RLK-4) promote cell elongation in Arabidopsis. I have chosen two of these FlRLKs for my studies: RLK-5, the most abundant pollen expressed member of the family and RLK10. My studies with RLK-5 suggest that it plays a significant role in pollination or fertilization since homozygous rlk-5 was never recovered from selfed heterozygous rlk-5 mutant. In addition to this, the reciprocal crosses with RLK-5/rlk-5 and wild type resulted in severe male transmission defect indicating that the rlk-5 mutation induces male sterility. This observation was found consistent with the pollen-specific expression pattern of RLK-5 suggested by microarray data and confirmed by histochemical GUS staining analysis of the RLK5p-GUS transgenic Arabidopsis. The RLK-5/rlk-5 pollen displayed no pollen-viability defects and the pollen tube growth in-vivo appears normal. Despite the unaffected pollen viability and apparent normal in-vivo pollen tube growth, the RLK-5/rlk-5 plants formed low seed set suggesting compromised fertilization. Additional analysis will be required to determine the basis of male deficiency and reduced seed sets in RLK5/rlk5 mutants. Loss of function mutations of RLK-10 (FERONIA/SIRENE) gene show failure in pollen tube growth arrest upon penetration of the female gametophyte, supernumerary pollen tube penetration of the ovule and reduced female fertility. Our studies with RLK-10 suggest that it is important for mediating a proper oxido-reductive condition within the ovule necessary for pollen tube rupture and fertilization of the female gametophyte. The multiple pollen tube entry phenotype of the Arabidopsis knockout mutant, rlk-10 correlated with decreased ROS level and de-esterified pectin in the filiform apparatus lining the synergid cell of its female gametophyte. These results establish an important signaling link between RLK-10 and ROS and pectin in a GEF-Rac/Rop regulated pathway in pollen tube-ovule interaction.

Chez les plantes à fleurs, l’ovaire est l’organe reproducteur femelle et il interagit de façon importante avec les gamètes mâles durant la croissance, le guidage, la réception et la rupture du tube pollinique ainsi que la fusion des gamètes. Le processus débute lorsque de nombreux gènes de l’ovule sont activés à longue distance lors de la réception du pollen sur le stigmate. Afin d’explorer les signaux provenant de l’ovule ayant un impact important sur les interactions pollen–pistil, particulièrement les molécules sécrétées impliquées dans la signalisation espècespécifique, l’expression génique des ovules sous forme d’ARNm ainsi et la sécrétion protéique ont été étudiées chez Solanum chacoense, une espèce diploïde de pomme de terre sauvage. S. chacoense a subi beaucoup d’hybridation interspécifique avec d’autres espèces sympathiques de solanacées, facilitant ainsi grandement l’étude des interactions pollen–ovule de façon espècespécifique ainsi que leur évolution. Dans ce projet, des ovules provenant de trois conditions différentes ont été comparés: des ovules matures de type sauvage, des ovules légèrement immatures, récoltés deux jours avant l’anthèse et des ovules provenant du mutant frk1 pour lesquels le sac embryonnaire est absent. Un séquençage d’ARN à haut débit a d’abord été effectué sur les ovules de type sauvage de S. chacoense afin de générer un assemblage de référence comprenant 33852 séquences codantes. D’autres séquençages ont été effectués sur les trois conditions d’ovules et sur les feuilles afin de faire une analyse d’expression différentielle des gènes. En comparaison avec les ovules de type sauvage, 818 gènes sont réprimés dans les ovules du mutant frk1. Un sous-groupe de 284 gènes, étaient également sous-exprimés dans les ovules légèrement immatures, suggérant un rôle spécifique dans les stades tardifs de la maturation du sac embryonnaire (stade de développent FG6 à FG7) ainsi que du guidage du tube pollinique, puisque ni les ovules du mutant frk1 ni ceux légèrement immatures ne sont capables d’attirer les tubes polliniques lors d’essais de croissance semi in vivo. De plus, 21% de ces gènes sont des peptides riches en cystéines (CRPs). En utilisant un transcriptome assemblé de novo provenant de deux proches parents de S. chacoense, S. gandarillasii et S. tarijense, une analyse d’orthologie a été effectuée sur ces CRPs, révélant une grande variabilité et une évolution rapide chez les solanacées. De nouveaux motifs de cystéine uniques à cette famille ont également été découverts. En comparant avec des études similaires chez Arabidopsis, le sac embryonnaire de S. chacoense montre un transcriptome fortement divergent, particulièrement en en ce qui a trait à la catégorisation fonctionnelle des gènes et de la similarité entre les gènes orthologues. De plus,même si la glycosylation n’est pas requise lors du guidage mycropylaire du tube pollinique chez Arabidopsis, Torenia ou le maïs, des extraits d’ovules glycosylés de S. chacoense sont capables d’augmenter la capacité de guidage de 18%. Cette étude est donc la première à montrer une corrélation entre glycosylation et le guidage du tube pollinique par l’ovule. En complément à l’approche transcriptomique, une approche protéomique portant sur les protéine sécrétées par l’ovule (le secrétome) a été utilisée afin d’identifier des protéines impliquées dans l’interaction entre ovule et tube pollinique. Des exsudats d’ovules matures (capables d’attirer le tube pollinique) et d’ovules immatures (incapables d’attirer le tube pollinique) ont été récoltés en utilisant une nouvelle méthode d’extraction par gravité permettant de réduire efficacement les contaminants cytosoliques à moins de 1% de l’échantillon. Un total de 305 protéines sécrétées par les ovules (OSPs) ont été identifiées par spectrométrie de masse, parmi lesquelles 58% étaient spécifiques aux ovules lorsque comparées avec des données de protéines sécrétées par des tissus végétatifs. De plus, la sécrétion de 128 OSPs est augmentée dans les ovules matures par rapport aux ovules immatures. Ces 128 protéines sont donc considérées en tant que candidates potentiellement impliquées dans la maturation tardive de l’ovule et dans le guidage du tube pollinique. Cette étude a également montré que la maturation du sac embryonnaire du stade FG6 au stade FG7 influence le niveau de sécrétion de 44% du sécrétome total de l’ovule. De façon surprenante, la grande majorité (83%) de ces protéines n’est pas régulée au niveau de l’ARN, soulignant ainsi l’importance de cette approche dans l’étude du guidage du tube pollinique comme complément essentiel aux études transcriptomiques. Parmi tous les signaux sécrétés par l’ovule et reliés au guidage, obtenus à partir des approches transcriptomiques et protéomiques décrites ci-haut, nous avons spécifiquement évalué l’implication des CRPs dans le guidage du tube pollinique par l’ovule chez S. chacoense, vu l’implication de ce type de protéine dans les interactions pollen-pistil et le guidage du tube pollinique chez d’autres espèces. Au total, 28 CRPs étaient présentes dans les ovules capables d’attirer le tube pollinique tout en étant absentes dans les ovules incapables de l’attirer, et ce, soit au niveau de l’ARNm et/ou au niveau du sécrétome. De celles-ci, 17 CRPs ont été exprimées dans un système bactérien et purifiées en quantité suffisante pour tester le guidage. Alors que des exsudats d’ovules ont été utilisés avec succès pour attirer par chimiotactisme le tube pollinique, les candidats exprimés dans les bactéries n’ont quant à eux pas été capables d’attirer les tubes polliniques. Comme l’utilisation de systèmes d’expression hétérologue eucaryote peut permettre un meilleur repliement et une plus grande activité des protéines, les candidats restants seront de nouveau exprimés, cette fois dans un système de levure ainsi que dans un système végétal pour produire les peptides sécrétés. Ceux-ci seront ensuite utilisés lors d’essais fonctionnels pour évaluer leur capacité à guider les tubes polliniques et ainsi isoler les attractants chimiques responsable du guidage du tube pollinique chez les solanacées comme S. chacoense.
In flowering plants, the ovary is the female reproductive organ that interacts extensively with the male gametophyte during pollen tube (PT) growth, guidance, reception, discharge and gamete fusion. The process begins when numerous ovule-expressed genes are activated when pollen lands on the stigma. To explore the ovular signals that have a great impact on successful pollen–pistil interactions, especially the secreted molecules that mediate species-specific signalling events, ovule mRNA expression and protein secretion profiles were studied in Solanum chacoense, a wild diploid potato species. Solanum chacoense has undergone extensive interspecific hybridization with sympatric solanaceous species that greatly facilitates the study of species-specific pollen–ovule interactions and evolution. In this project, three ovule conditions were studied: wild-type mature ovules, slightly immature ovules at two days before anthesis (2DBA), and frk1 mutant ovules that lack an embryo sac (ES). RNA-seq was performed on S. chacoense ovules to provide a scaffold assembly comprising 33852 CDS-containing sequences, then to provide read counts for differential gene expression analyses on three ovule conditions as well as on leaf. Compared to wild-type ovules, 818 genes were downregulated in frk1 ovules. A subset of 284 genes was concurrently under-expressed in 2DBA ovules, suggestive of their specific involvement in late stages of ES maturation (female gametophyte (FG), FG6 to FG7 developmental stage), as well as in PT guidance processes, as neither frk1 nor 2DBA ovules attract semi in vivo-grown PTs. Of these 284, 21% encoded cysteine-rich peptides (CRPs). Using de novo assembled ovule transcriptomes of two close relatives, S. gandarillasii and S. tarijense, an orthology survey was conducted on these CRPs, revealing their highly polymorphic nature among species and rapid evolution. Interestingly, novel cysteine motifs unique to this family were also uncovered. As compared to parallel studies in Arabidopsis, S. chacoense was found to possess a highly divergent ES transcriptome, in terms of both functional categories and individual ortholog similarities. Although glycosylation is not required for micropylar guidance cues to attract PTs in Arabidopsis, Torenia or maize, glycosylated ovule extracts from S. chacoense showed enhanced PT guidance competency by 18%. This is the first time a positive regulation between glycosylation and ovular PT guidance has been observed. As a complement to the transcriptomic approach, a proteomic approach using secreted proteins from the ovule (secretome) was employed to identify proteins involved in pollen–pistil interactions. Ovule exudates were collected from mature ovules (PT attracting) and immature ovules at 2DBA (PT nonattracting), using a novel tissue free-gravity extraction method (tf-GEM), which efficiently reduced the cytosolic contamination to less than 1%. Through mass spectrometry analyses, a total of 305 ovule-secreted proteins (OSPs) were identified, of which 58% were considered ovule-specific when compared to secretome studies conducted in other plant tissues. The secretion of 128 OSPs was upregulated in mature ovules vs. immature ovules. These OSPs were considered as candidate proteins involved in late ovule maturation and PT guidance. This study demonstrated that the ES maturation from FG6 to FG7 stages influenced the secretion status of 44% of ovule secretome. Surprisingly, the majority (83%) of these proteins were not regulated at the RNA level, vindicating this novel approach in the study of PT guidance as a robust complement to transcriptomic studies. Among all identified guidance-related ovular signals from the transcriptomic and proteomic approaches described above, we focused on the evaluation of the involvement of CRPs in ovular PT guidance of S. chacoense, due to the implication of various CRPs in pollen–pistil interactions and, especially, in PT guidance. A total of 28 CRPs were present in PT attracting ovules while being low or absent in nonattracting ovules, at the mRNA and/or protein secretion levels. Of these, 17 CRPs were expressed in bacteria and purified in sufficient amount for PT guidance assays. However, while ovule exudates were shown to induce PT chemotropism in the bead assay, refolded candidates did not show guidance competency. Since the use of eukaryotic protein expression systems might lead to better refolding and higher protein activity, the remaining candidates will be expressed in both yeast and plant-based expression systems and tested for their ability to attract PTs in a semi in-vivo assay, in order to lead us toward the isolation of PT guidance chemoattractants in solanaceous species like S. chacoense.

Stigmas of Arabidopsis thaliana carrying the exo70A1-1 mutation are defective in early pollen-pistil interactions; pollen grain adhesion to the stigma, pollen hydration, and penetration of the stigmatic surface by the pollen tube. Exo70 function in directed secretion has been linked to its ability to bind the phosphatidylinositides. To provide support that the classical, octomeric exocyst complex, which contains the Exo70 subunit, participates in compatible pollen-pistil interactions, this process was analyzed in plants deficient in Sec15, another subunit of the exocyst. Additionally, the role of phosphatidylinositol-4-phosphate (PI-4-P) in female fertility was evaluated through the use of the mutants ROOT HAIR DEFECTIVE 4-1 and PI4Kβ1β2 -/-, which have increased and decreased levels of PI-4-P respectively. Reduction of Sec15b levels or perturbation of PI-4-P in the stigma resulted in a reduced ability of of the transgenic/mutant stigmas to support pollen grain hydration; though all other stages of early pollen pistil interactions were unaffected.

Compatible interactions between male gametophytes (pollen) and the female reproductive organ (pistil) are essential for fertilization in flowering plants. Recognition at a molecular level allows “compatible” pollen grains to adhere/germinate on the stigma while pollen grains from unrelated plant species are largely ignored. The exocyst is a large eight subunit complex that is primarily involved in polarized secretion or regulated exocytosis in eukaryotic cells where it functions to tether vesicles to the plasma membrane. Recent research has implicated one of the Exo70 family members, Exo70A1, in compatible pollen-pistil interactions in Arabidopsis and Brassica. The loss of Exo70A1 in Arabidopsis Col-0 stigmas leads to the rejection of compatible pollen producing a “female sterile” phenotype. Through my research I have demonstrated that, driven by a stigma-specific promoter, an RFP:Exo70A1 fusion protein rescues this defect in exo70A1-1 mutant and Exo70A1 is found to be localized to the plasma membrane at flower opening.

RAC/ROPs are a unique group of RAS-related monomeric G proteins (small G proteins) that constitute the sole family of Rho GTPases in plants. RAC/ROPs, like their counterpart Rho GTPases from mammalian and fungal systems, can interconvert between an active GTP and an inactive GDP bound state. These powerful signaling molecules lie upstream in many diverse signal transduction pathways. Their controlled regulation is critical to overall plant fitness, growth, development, and responses to abiotic and biotic stress. RAC/ROP activation is regulated by guanine nucleotide exchange factors (GEFs). The work in this dissertation initiated from the characterization of the expression and functions of RopGEF1, a broadly expressed GEF that localizes to the sites of root hair formation and regulates polarized cell growth. The focus of this dissertation is on FERONIA (FER), an upstream regulator of RopGEF1 that was initially identified as a RopGEF1 interacting protein in a yeast two-hybrid screen. FERONIA (FER) was found to regulate RAC/ROP-mediated signal transduction for auxin-regulated root hair growth and a number of other auxin-dependent responses, consistent with RAC/ROPs playing an important role in auxin signaling. ^ In flowering plants, pollen tubes deliver sperm to fertilize the female gametophytes located inside the ovules. Once a pollen tube enters it subsequently bursts releasing its sperm, which enables fertilization. Mechanisms are in place to coordinate tube rupture as well as repel late arriving pollen tubes from an already visited ovule. In this way not yet visited ovules have higher chances of fertilization and fertilized ovules avoid polyspermy. In this work, FER is demonstrated to mediate NADPH oxidase-dependent reactive oxygen species production required for pollen tube rupture. In addition, FER is also required for de-esterified pectin deposition outside the female gametophyte, which correlates with the ability of ovules to divert late arriving pollen tubes. Furthermore, the extracellular domain of FER, which contains predicted carbohydrate-binding malectin-like domains, interacts directly with pectin. This finding establishes FER as a cell wall-binding receptor kinase in plants and illuminates unprecedented mechanisms of pollen tube reception. ^ The presence of carbohydrate binding motifs in the extracellular domain of FER and its direct interaction with pectin prompted my investigation of its role in sugar sensing and signaling pathways. My work shows that feronia (fer) mutants are hypersensitive to sucrose, while over-expressing FER suppresses sugar signaling. Moreover, fer mutants accumulate elevated levels of starch, which demonstrates defects in their distribution of carbohydrate resources in source (sugar producing) and sink (sugar consuming) tissues. The fer mutants also display sucrose-induced cell wall defects, alterations to cellular morphology, and enhanced production of the stress-associated pigment, anthocyanin. These results suggest that FER functions as a negative regulator of sugar sensing and signaling pathways. Additional support for this model stems from the finding that FER is highly expressed in tissues involved in sucrose transport and its expression is stimulated by sucrose. Furthermore, and consistent with the hormone abscisic acid being part of the overall sugar sensing network, fer mutant seedlings are hypersensitive to ABA and display enhanced ABA response gene expression. Taken together, the data presented in this dissertation reveal the regulation of widespread and essential plant functions including RAC/ROP signaling, pollen tube reception, cell wall integrity, and sugar signaling by a single cell surface receptor kinase.^

A concept is presented where the piston of a seabed based linear generator is directly driven by a buoy on the water surface. A spring is connected to the other end of the piston. Thereby the buoy absorbs energy in two ways. A large number of poles are used as an “electromagnetic gearbox” which gives a high rate of flux change in the stator despite the slow piston motion. The damping force is a function of the velocity and the electric output power. In the studied concept the power from the generator is rectified with a diode bridge. The results of theoretical studies of output power and its interaction with the dynamics of the equation of motion are presented. It is shown that the DC voltage can be tuned to optimize the power production for each wave climate.

Linear acoustic plane wave theory and a four pole parameter formulation are used to derive and solve the governing inhomogeneous equation for the forced pressure response in the simplified manifold model. The equations for estimating gas pressure pulsations in the annular cavity connected to an anechoic inlet pipe are presented. Complicated interactions between multiple cylinder valve ports in the suction manifold produce unexpected changes in the frequency response conditions for changes in the operating speed, and hence, the flow rate characteristics through the valves. From the addition of the delayed time for opening valve in the mass flow rate profiles and the comparison of the gas pulsations from experiment with those from simulation, the maximum strokes of the piston and the delayed times for opening valve can be estimated without solving the valve dynamic and thermodynamic equations. By applying the mass flow rate sinks at each valve as identified, the correlation between analytical and experimental results is shown to be much better than if the idealized, kinematically obtained source functions are used instead.