Ovules Of Plants Research Articles

Morphological characteristics of pollen from triploid watermelon and its fate on stigmas in a hybrid crop production system

Hybrid crop production is more reliant on pollinators compared to open-pollinated crops because they require cross-pollination between a male-fertile and a male-sterile line. Little is known about how stigma receipt of pollen from male-sterile genotypes affects reproduction in hybrids. Non-viable and non-compatible pollen cannot fertilise plant ovules, but may still interfere with pollination success. Here we used seedless watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) as a model hybrid plant, to evaluate the morphology, physiology, and movement of pollen from inter-planted genotypes (diploids and triploids). We found that pollen from triploids (‘Exclamation’ and ‘Royal Armada’) and diploids (‘SP-6’, ‘Summer Flavor 800’, and ‘Tiger’) was visually distinguishable. Pollen in triploids had more deformities (42.4–46%), tetrads (43–44%), and abnormal growth of callose plugs in pollen tubes. The amount of pollen in triploids to germinate on stigmas was low (8 ± 3%), and few pollen grains produced pollen tubes (6.5 ± 2%). Still, contrary to previous reports our results suggest that some viable pollen grains are produced by triploid watermelons. However, whilst honey bees can collect and deposit pollen from triploids onto stigmas, its effect on hybrid watermelon reproduction is likely to be minimal due to its low germination rate.

Brassinosteroid signaling regulates female germline specification in Arabidopsis

Unlike in humans and animals, plant germlines are specified de novo from somatic cells in the reproductive organs of the flower. In most flowering plant ovules, the female germline starts with the differentiation of one megaspore mother cell (MMC), which initiates a developmental program distinct from adjoining cells. Phytohormones act as a key player in physiological processes during plant development, in particular by providing positional information that supports localized differentiation events. However, little is known about the role of phytohormones for female germline initiation and establishment. Using Arabidopsis as a flowering plant model, we show that brassinosteroid (BR) biosynthesis and signaling components are accumulated in sporophytic cells of ovule primordia but not in the megaspore mother cell representing the precursor of the female germline. We further demonstrate that BR signaling restricts multiple sub-epidermal cells in the distal nucellus region of ovule primordia from acquiring MMC-like cell identity by transiently activating the WRKY23 transcription factor, expressed exclusively in L2 layer cells adjacent to the MMC. This activation is regulated through the BRI1 receptor and directly by the BZR1 transcriptional repressor family. Mutations in BR biosynthesis or signaling components and ectopic activation of BR signaling in MMCs induce multiple MMC-like cells. In summary, our findings elucidate a gene regulatory network that shows how the hormone BR generated in sporophytic ovule primordia cells restricts the origin of the female germline to a single cell.

MicroRNAs Involved in Regulatory Cytoplasmic Male Sterility by Analysis RNA-seq and Small RNA-seq in Soybean.

Cytoplasmic male sterility (CMS) is an important plant characteristic for exploiting heterosis to enhance crop traits during breeding. However, the CMS regulatory network remains unclear in plants, even though researchers have attempted to isolate genes associated with CMS. In this study, we performed high-throughput sequencing and degradome analyses to identify microRNAs (miRNAs) and their targets in a soybean CMS line (JLCMS9A) and its maintainer line (JLCMS9B). Additionally, the differentially expressed genes during reproductive development were identified using RNA-seq data. A total of 280 miRNAs matched soybean miRNA sequences in miRBase, including mature miRNAs and pre-miRNAs. Of the 280 miRNAs, 30, 23, and 21 belonged to the miR166, miR156, and miR171 families, respectively. Moreover, 410 novel low-abundant miRNAs were identified in the JLCMS9A and JLCMS9B flower buds. Furthermore, 303 and 462 target genes unique to JLCMS9A and JLCMS9B, respectively, as well as 782 common targets were predicted based on the degradome analysis. Target genes differentially expressed between the CMS line and the maintainer line were revealed by an RNA-seq analysis. Moreover, all target genes were annotated with diverse functions related to biological processes, cellular components, and molecular functions, including transcriptional regulation, the nucleus, meristem maintenance, meristem initiation, cell differentiation, auxin-activated signaling, plant ovule development, and anther development. Finally, a network was built based on the interactions. Analyses of the miRNA, degradome, and transcriptome datasets generated in this study provided a comprehensive overview of the reproductive development of a CMS soybean line. The data presented herein represent useful information for soybean hybrid breeding. Furthermore, the study results indicate that miRNAs might contribute to the soybean CMS regulatory network by modulating the expression of CMS-related genes. These findings lay the foundation for future studies on the molecular mechanisms underlying soybean CMS.

Morphological Features of the Anther Development in Tomato Plants with Non-Specific Male Sterility.

The study was devoted to morphological and cytoembryological analysis of disorders in the anther and pollen development of transgenic tomato plants with a normal and abnormal phenotype, which is characterized by the impaired development of generative organs. Various abnormalities in the structural organization of anthers and microspores were revealed. Such abnormalities in microspores lead to the blocking of asymmetric cell division and, accordingly, the male gametophyte formation. Some of the non-degenerated microspores accumulate a large number of storage inclusions, forming sterile mononuclear pseudo-pollen, which is similar in size and appearance to fertile pollen grain (looks like pollen grain). It was discussed that the growth of tapetal cells in abnormal anthers by increasing the size and ploidy level of nuclei contributes to this process. It has been shown that in transgenic plants with a normal phenotype, individual disturbances are also observed in the development of both male and female gametophytes. The reason for the developmental arrest of some ovules was the death of endosperm at different stages of the globular embryo. At the same time, noticeable hypertrophy of endothelial cells performing a secretory function was observed. In the ovules of transgenic plants with abnormalities, the endothelium forms a pseudo-embryo instead of the embryo sac, stimulating the development of parthenocarpic fruits. The data obtained in this study can be useful for a better understanding of the genetic and molecular mechanisms of cytoplasmic male sterility and parthenocarpic fruit development in tomatoes.

Distinct Differentiation Characteristics of Endothelium Determine Its Ability to Form Pseudo-Embryos in Tomato Ovules.

The endothelium is an additional cell layer, differentiating from the inner epidermis of the ovule integument. In tomato (Solanum lycopersicum L.), after fertilization, the endothelium separates from integument and becomes an independent tissue developing next to the growing embryo sac. In the absence of fertilization, the endothelium may proliferate and form pseudo-embryo. However, the course of the reorganization of endothelium into pseudo-embryo in tomato ovules is poorly understood. We aimed to investigate specific features of endothelium differentiation and the role of the endothelium in the development of fertilized and unfertilized tomato ovules. The ovules of tomato plants (“YaLF” line), produced by vegetative growth plants of transgenic tomato line expressing the ac gene, encoding chitin-binding protein from Amaranthus caudatus L., were investigated using light and transmission electron microscopy. We showed that in the fertilized ovule of normally developing fruit and in the unfertilized ovule of parthenocarpic fruit, separation of the endothelium from integument occurs via programmed death of cells of the integumental parenchyma, adjacent to the endothelium. Endothelial cells in normally developing ovules change their structural and functional specialization from meristematic to secretory and back to meristematic, and proliferate until seeds fully mature. The secretory activity of the endothelium is necessary for the lysis of dying cells of the integument and provides the space for the growth of the new sporophyte. However, in ovules of parthenocarpic fruits, pseudo-embryo cells do not change their structural and functional organization and remain meristematic, no zone of lysis is formed, and pseudo-embryo cells undergo programmed cell death. Our data shows the key role of the endothelium as a protective and secretory tissue, needed for the normal development of ovules.

Possible Roles ofBELL1 and Class III Homeodomain-Leucine Zipper Genes during Integument Evolution

Premise of research. According to the neosynangial hypothesis, sterilization of megasporangia and compaction of fertile appendages bearing megasporangia were critical steps for integument evolution. Ovules of bell1 (bel1) mutants in Arabidopsis thaliana can form ectopic nucelli in the chalazal domain instead of inner and outer integuments, while distances between ectopic nucelli expand when class III homeodomain-leucine zipper (HD-ZIPIII) genes are compromised in addition to bel1. These phenotypes imply that BEL1 and HD-ZIPIII genes would be participants in the sterilization and compaction steps, respectively. However, this interpretation is challenged by the observation that bel1 ovules also form an outgrowth in the chalazal domain. The outgrowth finally develops into a carpel-like structure (i.e., the ectopic nucelli would be formed on the placenta of this ectopic carpel). We revisited bel1 phenotypes to rule out this possibility and inferred how these genes contributed to integument evolution.Methodology. We observed development and expression of a carpel identity marker CRABS CLAW (CRC) in bel1 ovules. We compared expression of SPOROCYTELESS/NOZZLE (SPL/NZZ), a master regulator of nucellus formation, between bel1 and wild-type carpels by quantitative real-time polymerase chain reaction. We observed accumulation of PIN-FORMED 1 (PIN1) protein in triple mutants of HD-ZIPIII genes.Pivotal results. Morphological observation, as well as expression of CRC, suggested that ectopic nucelli are formed before induction of carpel identity. BEL1 represses SPL/NZZ expression. PIN1 expression was not altered in triple mutants of HD-ZIPIII genes, suggesting that they do not repress the nucellus-promoting pathway(s).Conclusions. The bel1 phenotype suggests that seed plant ovules have a repressed ability to form multiple nucelli, similar to fertile appendages of progymnosperms. BEL1 would have promoted sterilization of megasporangia by repressing SPL/NZZ. HD-ZIPIII genes would have controlled spacing between megasporangia in fertile appendages by regulating the size of the meristematic area rather than by repressing formation of extra megasporangia.

Establishing a framework for female germline initiation in the plant ovule.

Female gametogenesis in flowering plants initiates in the ovule, where a single germline progenitor differentiates from a pool of somatic cells. Germline initiation is a fundamental prerequisite for seed development but is poorly understood at the molecular level due to the location of the cells deep within the flower. Studies in Arabidopsis have shown that regulators of germline development include transcription factors such as NOZZLE/SPOROCYTELESS and WUSCHEL, components of the RNA-dependent DNA methylation pathway such as ARGONAUTE9 and RNA-DEPENDENT RNA POLYMERASE 6, and phytohormones such as auxin and cytokinin. These factors accumulate in a range of cell types from where they establish an environment to support germline differentiation. Recent studies provide fresh insight into the transition from somatic to germline identity, linking chromatin regulators, cell cycle genes, and novel mobile signals, capitalizing on cell type-specific methodologies in both dicot and monocot models. These findings are providing unique molecular and compositional insight into the mechanistic basis and evolutionary conservation of female germline development in plants.

Evolution towards minimum ovule size? Ovule size variations and the relative sizes of ovules to seeds.

Is there selection minimizing the costs of ovule production? Such selection should lead to a smaller ovule size in relation to seed size and, at the same time, smaller variation in ovule size within plants, the latter because the minimum structures and resources for functioning of ovules should be the same among ovules. Additionally, within species, ovule size should not depend on the plant's resource status. To confirm these predictions, we examined ovule and seed production for a variety of species. Among the 27 species studied, we found a significant negative dependence of the species mean of the coefficient of variation for plant ovule size on the ratio of the mean species seed size/mean species ovule size. Thus, the smaller the ovule size as compared with seed size, the smaller the degree of variation in ovule size. Among the 49 species studied, only two species showed significant positive dependence of mean ovule size on plant size. Although larger plants should have greater resources for ovule production, selection has not enhanced the production of large ovules in most species. These results suggest that there is selection minimizing the costs of ovule production.

Revisiting the Female Germline and Its Expanding Toolbox.

The Arabidopsis thaliana ovule arises as a female reproductive organ composed solely of somatic diploid cells. Among them, one cell will acquire a unique identity and initiate female germline development. In this review we explore the complex network that facilitates differentiation of this single cell, and consider how it becomes committed to a distinct developmental program. We highlight recent progress towards understanding the role of intercellular communication, cell competency, and cell-cycle regulation in the ovule primordium, and we discuss the possibility that distinct pathways restrict germline development at different stages. Importantly, these recent findings suggest a renaissance in plant ovule research, restoring the female germline as an attractive model to study cell communication and cell fate establishment in multicellular organs.

Pollen limitation and resource limitation affect the reproductive success of Medicago sativa L.

BackgroundA large proportion of the flowers and ovules of plants do not develop into fruits and seeds. Plant reproduction may be limited because of pollen limitation and resource limitation. Medicago sativa L. is an ecologically important species in northwest China. We conducted a pollen supplementation experiment to determine the degree of pollen limitation in this species and detect the possible effects of resource allocation on pollen supplementation. We crossed two factors, pollen level (natural condition and hand pollinated) and resource level (control, water added, and fertilizer added), to estimate the effects of pollen addition and resource limitation on the opening of flowers and seed set. We also analyzed the floral characters, visitation frequency of pollinators and pollinator activity to estimate the effect of pollinators on the reproduction of M. sativa.ResultsOur results indicated that addition of pollen to some flowers did not divert resources from other flowers and that the addition of pollen boosted the seed set per flower, with no effect on flower number. The primary effect of resource limitation was on the number of flowers produced; however, there was no significant effect on seed set per flower. These findings showed that pollen limitation was an important limiting factor for seed set. In addition, Andrena lebedevi Popov was identified as the most effective pollinator, and pollinator visiting and activity affected reproduction success in M. sativa.ConclusionsWe found outcrossing was dominant in the breeding system and insect pollination played an important role in outcrossing. These findings have identified the dominant factor influencing seed set of M. sativa. This study aspires to contribute to a better understanding of pollen limitation, resource limitation and reproductive success.

Structure, target-specificity and expression of PN_LNC_N13, a long non-coding RNA differentially expressed in apomictic and sexual Paspalum notatum

Key messagencRNA PN_LNC_N13 shows contrasting expression in reproductive organs of sexual and apomictic Paspalum notatum genotypes.Apomictic plants set genetically maternal seeds whose embryos derive by parthenogenesis from unreduced egg cells, giving rise to clonal offspring. Several Paspalum notatum apomixis related genes were identified in prior work by comparative transcriptome analyses. Here, one of these candidates (namely N13) was characterized. N13 belongs to a Paspalum gene family including 30–60 members, of which at least eight are expressed at moderate levels in florets. The sequences of these genes show no functional ORFs, but include segments of different protein coding genes. Particularly, N13 shows partial identity to maize gene BT068773 (RESPONSE REGULATOR 6). Secondary structure predictions as well as mature miRNA and target cleavage detection suggested that N13 is not a miRNA precursor. Moreover, N13 family members produce abundant 24-nucleotide small RNAs along extensive parts of their sequences. Surveys in the GREENC and CANTATA databases indicated similarity with plant long non-coding RNAs (lncRNAs) involved in splicing regulation; consequently, N13 was renamed as PN_LNC_N13. The Paspalum BT068773 predicted ortholog (N13TAR) originates floral transcript variants shorter than the canonical maize isoform and with possible structural differences between the apomictic and sexual types. PN_LNC_N13 is expressed only in apomictic plants and displays quantitative representation variation across reproductive developmental stages. However, PN_LNC_N13-like homologs and/or its derived sRNAs showed overall a higher representation in ovules of sexual plants at late premeiosis. Our results suggest the existence of a whole family of N13-like lncRNAs possibly involved in splicing regulation, with some members characterized by differential activity across reproductive types.

Pollen tube contents initiate ovule enlargement and enhance seed coat development without fertilization.

In angiosperms, pollen tubes carry two sperm cells toward the egg and central cells to complete double fertilization. In animals, not only sperm but also seminal plasma is required for proper fertilization. However, little is known regarding the function of pollen tube content (PTC), which is analogous to seminal plasma. We report that the PTC plays a vital role in the prefertilization state and causes an enlargement of ovules without fertilization. We termed this phenomenon as pollen tube-dependent ovule enlargement morphology and placed it between pollen tube guidance and double fertilization. Additionally, PTC increases endosperm nuclei without fertilization when combined with autonomous endosperm mutants. This finding could be applied in agriculture, particularly in enhancing seed formation without fertilization in important crops.

Specialization in the yucca-yucca moth obligate pollination mutualism: A role for antagonism?

Specialized brood pollination systems involve both mutualism and antagonism in the overall interaction and have led to diversification in both plants and insects. Although largely known for mutualism, the role of the antagonistic side of the interaction in these systems has been overlooked. Specialization may be driven by plant defenses to feeding by the insect larvae that consume and kill developing plant ovules. The interaction among yuccas and yucca moths is cited as a classic example of the importance of mutualism in specialization and diversification. Pollinators moths are very host specific, but whether this specificity is due to adult pollination ability or larval feeding ability is unclear. Here, I test the potential role of antagonism in driving specialization among yuccas and yucca moths. I examined the ability of the most-polyphagous yucca moth pollinator, Tegeticula yuccasella, to pollinate and develop on five Yucca species used across its range. Yucca species endemic to the Great Plains and Texas were transplanted to a common garden in Syracuse, New York and exposed to the local pollinator moth population over 3 years. Local moths visited all but one of the Yucca species, but had drastically lower rates of successful larval development on non-natal Yucca species in comparison to the local host species. Specialization in many brood pollination systems may be strongly influenced by the antagonistic rather than the mutualistic side of the overall interaction, suggesting that antagonistic coevolution is a possible source of diversification.

Deep sequencing discovery and profiling of conserved and novel miRNAs in the ovule of Ginkgo biloba

High-throughput sequencing and subsequent analysis identified multiple miRNAs closely related to ovule, indicating that miRNAs are important in Ginkgo biloba ovule. MicroRNAs (miRNAs) are small, noncoding, regulatory RNAs that play crucial regulatory roles in the process of plant growth and development. However, limited information regarding their functions in gymnosperm reproduction is available. Here, we used high-throughput sequencing combined with computational analysis to identify and characterize miRNAs from ovules of G. biloba, and identified 34 conserved miRNA families and 99 novel miRNAs. The precursor sequences of several of the conserved and novel miRNAs were further validated by RT-PCR and sequencing. Furthermore, we found that some target genes, e.g. MYB, homeodomain-leucine zipper (HD-ZIPIII) and auxin response factor (ARF), may be involved in ovule development, and that the significantly enriched pathways of some miRNA targets were related to plant–pathogen interactions and the biosynthesis of secondary metabolites. Twenty-six conserved miRNA families were found to be expressed in both leaves and ovules, while miRNA156, miRNA164, miRNA167, miRNA169, miRNA172 and miRNA390 were up-regulated in ovules. Thus, multiple miRNAs closely related to G. biloba ovule development were identified, resulting in a greater understanding of the important regulatory functions of miRNAs in plant ovules.

The Plant Ovule Secretome: A Different View toward Pollen-Pistil Interactions.

During plant sexual reproduction, continuous exchange of signals between the pollen and the pistil (stigma, style, and ovary) plays important roles in pollen recognition and selection, establishing breeding barriers and, ultimately, leading to optimal seed set. After navigating through the stigma and the style, pollen tubes (PTs) reach their final destination, the ovule. This ultimate step is also regulated by numerous signals emanating from the embryo sac (ES) of the ovule. These signals encompass a wide variety of molecules, but species-specificity of the pollen-ovule interaction relies mainly on secreted proteins and their receptors. Isolation of candidate genes involved in pollen-pistil interactions has mainly relied on transcriptomic approaches, overlooking potential post-transcriptional regulation. To address this issue, ovule exudates were collected from the wild potato species Solanum chacoense using a tissue-free gravity-extraction method (tf-GEM). Combined RNA-seq and mass spectrometry-based proteomics led to the identification of 305 secreted proteins, of which 58% were ovule-specific. Comparative analyses using mature ovules (attracting PTs) and immature ovules (not attracting PTs) revealed that the last maturation step of ES development affected almost half of the ovule secretome. Of 128 upregulated proteins in anthesis stage, 106 were not regulated at the mRNA level, emphasizing the importance of post-transcriptional regulation in reproductive development.

PnTgs1-like expression during reproductive development supports a role for RNA methyltransferases in the aposporous pathway.

BackgroundIn flowering plants, apomixis (asexual reproduction via seeds) is widely believed to result from failure of key regulators of the sexual female reproductive pathway. In the past few years, both differential display and RNA-seq comparative approaches involving reproductive organs of sexual plants and their apomictic counterparts have yielded extensive lists of candidate genes. Nevertheless, only a limited number of these genes have been functionally characterized, with few clues consequently available for understanding the molecular control of apomixis. We have previously identified several cDNA fragments with high similarity to genes involved in RNA biology and with differential amplification between sexual and apomictic Paspalum notatum plants. Here, we report the characterization of one of these candidates, namely, N69 encoding a protein of the S-adenosyl-L-methionine-dependent methyltransferases superfamily. The purpose of this work was to extend the N69 cDNA sequence and to characterize its expression at different developmental stages in both sexual and apomictic individuals.ResultsMolecular characterization of the N69 cDNA revealed homology with genes encoding proteins similar to yeast and mammalian trimethylguanosine synthase/PRIP-interacting proteins. These proteins play a dual role as ERK2-controlled transcriptional coactivators and mediators of sn(o)RNA and telomerase RNA cap trimethylation, and participate in mammals and yeast development. The N69-extended sequence was consequently renamed PnTgs1-like. Expression of PnTgs1-like during reproductive development was significantly higher in floral organs of sexual genotypes compared with apomicts. This difference was not detected in vegetative tissues. In addition, expression levels in reproductive tissues of several genotypes were negatively correlated with facultative apomixis rates. Moreover, in situ hybridization observations revealed that PnTgs1-like expression is relatively higher in ovules of sexual plants throughout development, from premeiosis to maturity. Tissues where differential expression is detected include nucellar cells, the site of aposporous initials differentiation in apomictic genotypes.ConclusionsOur results indicate that PnTgs1-like (formerly N69) encodes a trimethylguanosine synthase-like protein whose function in mammals and yeast is critical for development, including reproduction. Our findings also suggest a pivotal role for this candidate gene in nucellar cell fate, as its diminished expression is correlated with initiation of the apomictic pathway in plants.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0297-0) contains supplementary material, which is available to authorized users.

Deposition of callose in young ovules of two Taraxacum species varying in the mode of reproduction.

Although callose occurs during megasporogenesis in most flowering plants, the knowledge about its general function and the mechanisms by which the callose layer is formed in particular places is still not sufficient. The results of previous studies suggest a total lack of callose in the ovules of diplosporous plants in which meiosis is omitted or disturbed. This report is the first documentation of callose events in dandelions ovules. We demonstrated the pattern of callose deposition during the formation of megaspores through diplospory of Taraxacum type and during normal meiotic megasporogenesis in apomictic triploid Taraxacum atricapillum and amphimictic diploid Taraxacum linearisquameum. We found the presence of callose in the megasporocyte wall of both diplosporous and sexual dandelions. However, in a diplosporous dandelion, callose predominated at the micropylar pole of megaspore mother cell (MMC) which may be correlated with abnormal asynaptic meiosis and may indicate diplospory of the Taraxacum type. After meiotic division, callose is mainly deposited in the walls between megaspores in tetrads and in diplodyads. In subsequent stages, callose gradually disappears around the chalazal functional megaspore. However, some variations in the pattern of callose deposition within tetrad may reflect variable positioning of the functional megaspore (FM) observed in the ovules of T. linearisquameum.

Fabrication of microcage arrays to fix plant ovules for long-term live imaging and observation

The long-term observation of plant ovules is important to investigate embryogenesis and the development occurring inside. However, it has been difficult to observe the ovule consistently in a specific position because ovules are randomly dispersed on a substrate with conventional methods. In this work, we fabricated PDMS microcage arrays to fix plant ovules from Arabidopsis thaliana and observed them over a long period. Microcages were designed based on experimental data of ovule growth so that ovules could be positioned inside the cage and observed in real time. First, we performed the sieving test to investigate the relationship between ovule size and different microcage widths. Next, we performed ovule culture for a week using microcage arrays developed based on the results of sieving tests. We successfully positioned and fixed ovules inside the microcages and confirmed that the ovules did not move from their original positions even though the culture dish was frequently moved for observation and incubation. Moreover, we observed that the ovules grew inside the cages without being affected due to the flexibility of PDMS. Thus, we confirmed the validity of microcage arrays as the useful tool to fix and culture plant ovules for long-term observation. We expect that microcage arrays could be widely used as the essential device for pursuing scientific findings in further researches of plant embryogenesis and reproduction.

The influence of habitat autocorrelation on plants and their seed-eating pollinators

Model systems for studying mutualism costs and benefits include the many species of plants that rely on seed-eating pollinators for their reproduction. Empirical studies of these interactions show that mutualism costs and benefits can vary greatly within populations. Here we investigate the role of plant habitat autocorrelation on mutualism properties when mutualist dispersal is limited. We build a spatially explicit individual-based model of an obligate mutualism that includes a plant and its obligate seed-eating pollinator. We also model exploiters of this mutualism, which do not pollinate, but compete with pollinators for pollinated plant ovules in which to develop. We test how the autocorrelation of habitable plant environment affects pollinator production, seed production, pollinator visitation to plants, and the persistence of exploiters at different dispersal distances and rates of exploitation. We find that positive habitat autocorrelation increases the mean number of pollinator visits to plants. More frequent pollinator visitation to plants increases the probability that a random plant will be pollinated, but also the probability of pollinator oviposition into plant ovules at the cost of a developing seed. This process leads to spatial variation in the production of pollinators versus seeds. For a given scale of habitat autocorrelation, the turnover of this variation decreases when pollinator dispersal distance is high. Exploiters of the mutualism dramatically lower the number of pollinator visits per flower, which decreases pollinator production, seed production, and mutualist densities. Exploiters persist with mutualists when the mean number of pollinator visits per plant is neither too low, nor too high. When the mean number of pollinator visits a plant receives is too low, overexploitation and the extinction of both mutualists and exploiters follows; a high mean number of pollinator visits results in the competitive exclusion of exploiters by pollinators. Because the autocorrelation of habitat strongly affects the number of pollinator visits per flower, our results show that habitat autocorrelation can influence key mutualism properties and the susceptibility of mutualisms to exploitation.

Genetic analysis of ectopic growth suppression during planar growth of integuments mediated by the Arabidopsis AGC protein kinase UNICORN

BackgroundThe coordination of growth within a tissue layer is of critical importance for tissue morphogenesis. For example, cells within the epidermis undergo stereotypic cell divisions that are oriented along the plane of the layer (planar growth), thereby propagating the layered epidermal structure. Little is known about the developmental control that regulates such planar growth in plants. Recent evidence suggested that the Arabidopsis AGC VIII protein kinase UNICORN (UCN) maintains planar growth by suppressing the formation of ectopic multicellular protrusions in several floral tissues including integuments. In the current model UCN controls this process during integument development by directly interacting with the ABERRANT TESTA SHAPE (ATS) protein, a member of the KANADI (KAN) family of transcription factors, thereby repressing its activity. Here we report on the further characterization of the UCN mechanism.ResultsPhenotypic analysis of flowers of ucn-1 plants impaired in floral homeotic gene activity revealed that any of the four floral whorls could produce organs carrying ucn-1 protrusions. The ectopic outgrowths of ucn integuments did not accumulate detectable signals of the auxin and cytokinin reporters DR5rev::GFP and ARR5::GUS, respectively. Furthermore, wild-type and ucn-1 seedlings showed similarly strong callus formation upon in vitro culture on callus-inducing medium. We also show that ovules of ucn-1 plants carrying the dominant ats allele sk21-D exhibited more pronounced protrusion formation. Finally ovules of ucn-1 ett-1 double mutants and ucn-1 ett-1 arf4-1 triple mutants displayed an additive phenotype.ConclusionsThese data deepen the molecular insight into the UCN-mediated control of planar growth during integument development. The presented evidence indicates that UCN downstream signaling does not involve the control of auxin or cytokinin homeostasis. The results also reveal that UCN interacts with ATS independently of an ATS/ETT complex required for integument initiation and they further emphasize the necessity to balance UCN and ATS proteins during maintenance of planar growth in integuments.