Apospory appears to accelerate onset of meiosis and sexual embryo sac formation in sorghum ovules

<p>Abstract</p> <p>Background</p> <p>Genetically unreduced (2<it>n</it>) embryo sacs (ES) form in ovules of gametophytic apomicts, the 2<it>n </it>eggs of which develop into embryos parthenogenetically. In many apomicts, 2<it>n </it>ES form precociously during ovule development. Whether meiosis and sexual ES formation also occur precociously in facultative apomicts (capable of apomictic and sexual reproduction) has not been studied. We determined onset timing of meiosis and sexual ES formation for 569 <it>Sorghum bicolor </it>genotypes, many of which produced 2<it>n </it>ES facultatively.</p> <p>Results</p> <p>Genotype differences for onset timing of meiosis and sexual ES formation, relative to ovule development, were highly significant. A major source of variation in timing of sexual germline development was presence or absence of apomictic ES, which formed from nucellar cells (apospory) in some genotypes. Genotypes that produced these aposporous ES underwent meiosis and sexual ES formation precociously. Aposporous ES formation was most prevalent in subsp. <it>verticilliflorum </it>and in breeding lines of subsp. <it>bicolor</it>. It was uncommon in land races.</p> <p>Conclusions</p> <p>The present study adds meiosis and sexual ES formation to floral induction, apomictic ES formation, and parthenogenesis as processes observed to occur precociously in apomictic plants. The temporally diverse nature of these events suggests that an epigenetic memory of the plants' apomixis status exists throughout its life cycle, which triggers, during multiple life cycle phases, temporally distinct processes that accelerate reproduction.</p

Transcriptome Analysis of Differentially Expressed Genes at Pre-Meiotic Developmental Stage in Pennisetum Hybrids with Contrasting Modes of Reproduction

Apomixis is an asexual reproduction through seeds where embryo develops without meiosis and fertilization. It is widely distributed throughout plant kingdom, but is more prevalent in families like Asteraceae, Rosaceae and Poaceae (Carman, 1997). This trait is highly desirable for fixing heterosis in F1 hybrids with significant implications for crop improvement (Dwivedi et al., 2007). Therefore it is necessary to unravel the molecular and genetic basis of apomixis to tap its potential. Pennisetum is an important genus of the Poaceae family which contains a wide range of species exhibiting wide variability in morphological, molecular, and reproductive traits (Jauhar, 1998). It includes many apomictic wild relatives of cultivated pearl millet (Pennisetum glaucum), some of them used extensively for introgression and molecular studies on apomixis, such as P. squamulatum, P. ciliare, and P. orientale (Ozias-Akins and Van Dijk, 2007; Kaushal et al., 2010). In order to identify putative genes involved in expression of apomixis, the genes showing differential expression across sexual and apomictic genotypes may be identified and characterized. A variety of methods are available for such molecular differential screening. These include differential display, fingerprinting techniques like cDNA AFLP, Subtractive hybridization, Micro array and Gene Chip technologies. These methods are employed for different purposes based on their convenience, sensitivity, automation and throughput. Texa with contrasting modes of reproduction are resources to identify genes involved in apomixis phenomenon. Broadly, the differentiation in reproduction pathway between apomictic and sexual lines is at three steps viz. pre-meiotic (including genes involved in preparing of ovule to enter into apomeiotic pathway), meiotic (genes involved in apomeiosis and embryo-sac development) and post-meiotic (genes involved in embryo-sac maturation and preparing for parthenogenesis). The present study was aimed to carry out a comprehensive transcriptome survey to identify differentially expressed transcripts in ovules of aposporous Pennisetum hybrid during the pre-meiotic stage of apomictic reproduction

Ploidy Dependent Expression of Apomixis Components in Guinea Grass (\u3cem\u3ePanicum maximum\u3c/em\u3e Jacq.)

Apomixis is an asexual method of reproduction through seeds. The potential of apomixis has been envisaged as “asexual revolution” by virtue of its capacity to fix hybrid vigour, a much desirable feature in breeding of agricultural crops. The genetic mechanism of apomixis regulation is complex and is believed to be largely affected by polyploidy (Nogler 1984). Expression of apomixis essentially contains three components, viz. apomeiosis (formation of unreduced egg cell), parthenogenesis (fertilization independent embryo development) and functional endosperm development (autonomous or psuedogamous). In contrast to previous reports, the evidence has now gathered that these three components can be functionally uncoupled and recombination is possible between these components (Kaushal, et al., 2008). Such recombinations lead to diversity in seed development pathways and also provide a mechanism to modify the ploidy levels. Uncoupling of apomeiosis from parthenogenesis may yield high frequency of triploids and haploids. Utilizing this partitioning principle we have generated a ploidy series following a Hybridization–supplemented Apomixis-components Partitioning Approach (HAPA) in guinea grass, a model crop for polyploidy and apomixis research, (Kaushal et al., 2009). From a single 4x (2n=32) progenitor, a ploidy series has been developed represented by 3x, 4x, 5x, 6x, 7x, 8x, 9x and 11x cytotypes. This ploidy series offers advantage of studying ploidy regulated gene expression. There have been sporadic reports on effect of polyploidy in expression of apomixis per se; however information on effect of polyploidy on individual apomixis components is not available. The guinea grass ploidy series with sequentially added monoploid genome doses has been used in present study to understand the effect of ploidy levels on phenotypic expression of partitioned apomixis components

Apospory and Diplospory in Diploid Boechera (Brassicaceae) May Facilitate Speciation by Recombination-Driven Apomixis-to-Sex Reversals

Apomixis (asexual seed formation) in angiosperms occurs either sporophytically, through adventitious embryony, or gametophytically, where an unreduced female gametophyte (embryo sac) forms and produces an unreduced egg that develops into an embryo parthenogenetically. Multiple types of gametophytic apomixis occur, and these are differentiated based on where and when the unreduced gametophyte forms, a process referred to as apomeiosis. Apomeiotic gametophytes form directly from ameiotic megasporocytes, as in Antennaria-type diplospory, from unreduced spores derived from 1st division meiotic restitutions, as in Taraxacum-type diplospory, or from cells of the ovule wall, as in Hieracium-type apospory. Multiple types of apomeiosis occasionally occur in the same plant, which suggests that the different types occur in response to temporal and/or spatial shifts in termination of sexual processes and onset timing of apomeiosis processes. To better understand the origins and evolutionary implications of apomixis in Boechera (Brassicaceae), we determined apomeiosis type for 64 accessions representing 44 taxonomic units. Plants expressing apospory and diplospory were equally common, and these generally produced reduced and unreduced pollen, respectively. Apospory and diplospory occurred simultaneously in individual plants of seven taxa. In Boechera, apomixis perpetuates otherwise sterile or semisterile interspecific hybrids (allodiploids) through multiple generations. Accordingly, ample time, in these multigenerational clones, is available for rare meioses to produce haploid, intergenomically recombined male and female gametes. The fusion of such gametes could then produce segmentally autoploidized progeny. If sex re-emerges among such progeny, then new and genomically unique sexual species could evolve. Herein, we present evidence that such apomixis-facilitated speciation is occurring in Boechera, and we hypothesize that it might also be occurring in facultatively apomictic allodiploids of other angiospermous taxa

Possible mechanisms of hypotension produced 70% alcoholic extract of Terminalia arjuna (L.) in anaesthetized dogs

BACKGROUND: The bark of Terminalia arjuna L. (Combretaceae) is used in Ayurveda since ancient times for the treatment of cardiac disorders. Previous laboratory investigations have demonstrated the use of the bark in cardiovascular complications. The present study was aimed to find the effect of 70% alcoholic extract of Terminalia arjuna on anaesthetized dog blood pressure and probable site of action. METHODS: Six dogs were anaesthetized with intraperitoneal injection of thiopental sodium and the blood pressure of each dog (n = 6) was measured from the left common carotid artery connected to a mercury manometer on kymograph. The femoral vein was cannulated for administration of drug solutions. The extract of T. arjuna (dissolved in propylene glycol) in the dose range of 5 to 15 mg/kg were administered intravenously in a pilot study and the dose (6 mg/kg) which produced appreciable hypotension was selected for further studies. RESULTS: Intravenous administration of T. arjuna produced dose-dependent hypotension in anaesthetized dogs. The hypotension produced by 6 mg/kg dose of the extract was blocked by propranolol but not by atropine or mepyramine maleate. This indicates that muscarinic or histaminergic mechanisms are not likely to be involved in the hypotension produced by the extract. The blockade by propranolol of the hypotension produced by T. arjuna indicates that the extract might contain active compound(s) possessing adrenergic ß(2)-receptor agonist action and/or that act directly on the heart muscle. CONCLUSION: The results indicated the likely involvement of peripheral mechanism for hypotension produced by the 70% alcoholic extract of Terminalia arjuna and lends support for the claims of its traditional usage in cardiovascular disorders

Partitioning Apomixis Components to Understand and Utilize Gametophytic Apomixis

Apomixis is a method of reproduction to generate clonal seeds and offers tremendous potential to fix heterozygosity and hybrid vigor. The process of apomictic seed development is complex and comprises three distinct components, viz., apomeiosis (leading to formation of unreduced egg cell), parthenogenesis (development of embryo without fertilization) and functional endosperm development. Recently, in many crops, these three components are reported to be uncoupled leading to their partitioning. This review provides insight into the recent status of our understanding surrounding partitioning apomixis components in gametophytic apomictic plants and research avenues that it offers to help understand the biology of apomixis. Possible consequences leading to diversity in seed developmental pathways, resources to understand apomixis, inheritance and identification of candidate gene(s) for partitioned components, as well as contribution towards creation of variability are all discussed. The potential of Panicum maximum, an aposporous crop, is also discussed as a model crop to study partitioning principle and effects. Modifications in cytogenetic status, as well as endosperm imprinting effects arising due to partitioning effects, opens up new opportunities to understand and utilize apomixis components, especially towards synthesizing apomixis in crops

Apospory and Diplospory in Diploid Boechera (Brassicaceae) May Facilitate Speciation by Recombination-Driven Apomixis-to-Sex Reversals

Apomixis (asexual seed formation) in angiosperms occurs either sporophytically, through adventitious embryony, or gametophytically, where an unreduced female gametophyte (embryo sac) forms and produces an unreduced egg that develops into an embryo parthenogenetically. Multiple types of gametophytic apomixis occur, and these are differentiated based on where and when the unreduced gametophyte forms, a process referred to as apomeiosis. Apomeiotic gametophytes form directly from ameiotic megasporocytes, as in Antennaria-type diplospory, from unreduced spores derived from 1st division meiotic restitutions, as in Taraxacum-type diplospory, or from cells of the ovule wall, as in Hieracium-type apospory. Multiple types of apomeiosis occasionally occur in the same plant, which suggests that the different types occur in response to temporal and/or spatial shifts in termination of sexual processes and onset timing of apomeiosis processes. To better understand the origins and evolutionary implications of apomixis in Boechera (Brassicaceae), we determined apomeiosis type for 64 accessions representing 44 taxonomic units. Plants expressing apospory and diplospory were equally common, and these generally produced reduced and unreduced pollen, respectively. Apospory and diplospory occurred simultaneously in individual plants of seven taxa. In Boechera, apomixis perpetuates otherwise sterile or semisterile interspecific hybrids (allodiploids) through multiple generations. Accordingly, ample time, in these multigenerational clones, is available for rare meioses to produce haploid, intergenomically recombined male and female gametes. The fusion of such gametes could then produce segmentally autoploidized progeny. If sex re-emerges among such progeny, then new and genomically unique sexual species could evolve. Herein, we present evidence that such apomixis-facilitated speciation is occurring in Boechera, and we hypothesize that it might also be occurring in facultatively apomictic allodiploids of other angiospermous taxa

Formation of a gold-carbon dot nanocomposite with superior catalytic ability for the reduction of aromatic nitro groups in water

We report the synthesis of a gold-carbon dot nanocomposite and its utility as a recyclable catalyst for the reduction of aromatic nitro groups. The presence of carbon dots on gold nanosurfaces enhanced the reduction rate by two-fold

Null dust in canonical gravity

We present the Lagrangian and Hamiltonian framework which incorporates null dust as a source into canonical gravity. Null dust is a generalized Lagrangian system which is described by six Clebsch potentials of its four-velocity Pfaff form. The Dirac--ADM decomposition splits these into three canonical coordinates (the comoving coordinates of the dust) and their conjugate momenta (appropriate projections of four-velocity). Unlike ordinary dust of massive particles, null dust therefore has three rather than four degrees of freedom per space point. These are evolved by a Hamiltonian which is a linear combination of energy and momentum densities of the dust. The energy density is the norm of the momentum density with respect to the spatial metric. The coupling to geometry is achieved by adding these densities to the gravitational super-Hamiltonian and supermomentum. This leads to appropriate Hamiltonian and momentum constraints in the phase space of the system. The constraints can be rewritten in two alternative forms in which they generate a true Lie algebra. The Dirac constraint quantization of the system is formally accomplished by imposing the new constraints as quantum operator restrictions on state functionals. We compare the canonical schemes for null and ordinary dust and emhasize their differences.Comment: 25 pages, REVTEX, no figure

Integrating transcriptomic and proteomic data for accurate assembly and annotation of genomes

© 2017 Wong et al.; Published by Cold Spring Harbor Laboratory Press. Complementing genome sequence with deep transcriptome and proteome data could enable more accurate assembly and annotation of newly sequenced genomes. Here, we provide a proof-of-concept of an integrated approach for analysis of the genome and proteome of Anopheles stephensi, which is one of the most important vectors of the malaria parasite. To achieve broad coverage of genes, we carried out transcriptome sequencing and deep proteome profiling of multiple anatomically distinct sites. Based on transcriptomic data alone, we identified and corrected 535 events of incomplete genome assembly involving 1196 scaffolds and 868 protein-coding gene models. This proteogenomic approach enabled us to add 365 genes that were missed during genome annotation and identify 917 gene correction events through discovery of 151 novel exons, 297 protein extensions, 231 exon extensions, 192 novel protein start sites, 19 novel translational frames, 28 events of joining of exons, and 76 events of joining of adjacent genes as a single gene. Incorporation of proteomic evidence allowed us to change the designation of more than 87 predicted noncoding RNAs to conventional mRNAs coded by protein-coding genes. Importantly, extension of the newly corrected genome assemblies and gene models to 15 other newly assembled Anopheline genomes led to the discovery of a large number of apparent discrepancies in assembly and annotation of these genomes. Our data provide a framework for how future genome sequencing efforts should incorporate transcriptomic and proteomic analysis in combination with simultaneous manual curation to achieve near complete assembly and accurate annotation of genomes