Additional nucleoli and NOR activity during meiotic prophase I in larch (Larix decidua Mill.)

Core spliceosomal Sm proteins as constituents of cytoplasmic mRNPs in plants

In recent years, research has increasingly focused on the key role of post-transcriptional regulation of messenger ribonucleoprotein (mRNP) function and turnover. As a result of the complexity and dynamic nature of mRNPs, the full composition of a single mRNP complex remains unrevealed and mRNPs are poorly described in plants. Here we identify canonical Sm proteins as part of the cytoplasmic mRNP complex, indicating their function in the post-transcriptional regulation of gene expression in plants. Sm proteins comprise an evolutionarily ancient family of small RNA-binding proteins involved in pre-mRNA splicing. The latest research indicates that Sm could also impact on mRNA at subsequent stages of its life cycle. In this work we show that in the microsporocyte cytoplasm of Larix decidua, the European larch, Sm proteins accumulate within distinct cytoplasmic bodies, also containing polyadenylated RNA. To date, several types of cytoplasmic bodies involved in the post-transcriptional regulation of gene expression have been described, mainly in animal cells. Their role and molecular composition in plants remain less well established, however. A total of 222 mRNA transcripts have been identified as cytoplasmic partners for Sm proteins. The specific colocalization of these mRNAs with Sm proteins within cytoplasmic bodies has been confirmed via microscopic analysis. The results from this work support the hypothesis, that evolutionarily conserved Sm proteins have been adapted to perform a whole repertoire of functions related to the post-transcriptional regulation of gene expression in Eukaryota. This adaptation presumably enabled them to coordinate the interdependent processes of splicing element assembly, mRNA maturation and processing, and mRNA translation regulation, and its degradation.

Spatio-temporal localization of LlBOP following early events of floral abscission in yellow lupine

The phenomenon of excessive flower abscission in yellow lupine is a process of substantial interest to the agricultural industries, because it substantially affects the yield. The aim of this work was to provide an analysis of the changes taking place precisely in the abscission zone (AZ) during early stages of flower separation. We put particular emphasis on mRNA accumulation of BOP (BLADE ON PETIOLE) gene encoding a transcriptional factor so far considered to be essential for AZ formation. Our results show that the AZ displays a particular transcriptional network active in the specific stages of its function, as reflected by the expression profile of LlBOP. Noteworthy, spatio-temporal LlBOP transcript accumulation in the elements of pedicel vascular tissue reveals divergent regulatory mechanism of its activity. We have also found that AZ cells accumulate reactive oxidative species following abscission and what is more, become active due to the increasing amount of uridine-rich small nuclear RNA, accompanied by poly(A) mRNA intensive synthesis. Our paper is a novel report for BOP involvement in the AZ functioning in relation to the whole transcriptional activity of AZ and overall discussed regarding BOP role as a potential mobile key regulator of abscission.

Cytogenetic Abnormalities in Seed Progenies of Pinus Pallasiana D. Don Stands from Technogenic Polluted Lands in the Steppe of Ukraine

In this study, we compare the pathological mitosis rates, chromosomal abnormalities and nucleolar organizer activity in Pinus pallasiana D. Don seedlings from natural population in the Crimean Mountains and from the urban plantations in the steppe of Ukraine. On the stages of anaphase and telophase of mitosis, such chromosomal abnormalities as bridges were most often found in the seeds of plantations exposed to air pollutants, whereas lead and agglutination of chromosomes were found in seeds from iron ore dump stands. Our studies have shown that P. pallasiana can be used for genotoxic monitoring of technogenic polluted lands.

Ribosomal DNA loci derived from Brachypodium stacei are switched off for major parts of the life cycle of Brachypodium hybridum

Nucleolar dominance is an epigenetic phenomenon that occurs in some plant and animal allopolyploids and hybrids, whereby only one ancestral set of 35S rRNA genes retains the ability to form the nucleolus while the rDNA loci derived from the other progenitor are transcriptionally silenced. There is substantial evidence that nucleolar dominance is regulated developmentally. This study focuses upon the establishment and/or maintenance of nucleolar dominance during different stages of development in the model grass allotetraploid Brachypodium hybridum. Fluorescence in situ hybridization with a 25S rDNA probe to cells in three-dimensional cytogenetic preparations showed that nucleolar dominance is present not only in root meristematic and differentiated cells of this species, but also in male meiocytes at prophase I, tetrads of microspores, and different embryonic tissues. The inactive state of Brachypodium stacei-originated rDNA loci was confirmed by silver staining. Only B. distachyon-derived 35S rDNA loci formed nucleoli in the aforementioned tissues, whereas B. stacei-like loci remained highly condensed and thus transcriptionally suppressed. The establishment of nucleolar dominance during earlier stages of B. hybridum embryo development cannot be ruled out. However, we propose that gradual pseudogenization of B. stacei-like loci in the evolution of the allotetraploid seems to be more likely.

Obestatin protects and reverses nonalcoholic fatty liver disease and its associated insulin resistance in rats via inhibition of food intake, enhancing hepatic adiponectin signaling, and blocking ghrelin acylation

This study investigated the ameliorative and protective effects of long-term obestatin administration (80 nmol/kg/ intraperitoneal injection (i.p.)) on the pathogenesis of high-fat diet (HFD) induced nonalcoholic fatty liver disease (NAFLD) in rats. Rats (n = 8/group) were divided as control, NAFLD, NAFLD + Simvastatin, NAFLD + obestatin, NAFLD then obestatin, and obestatin then NAFLD. Obestatin co -or post-therapy significantly reduced hepatomegaly and reversed hyperlipidemia, hepatic lipid accumulation, and insulin resistance (IR). Mechanistically obestatin treatments in these rats significantly prevented the increases in final body weights and food intake. Concomitantly, it enhanced circulatory adiponectin levels and hepatic signaling as evident by elevated hepatic protein levels of adiponectin receptors (adipoRII), carnitine palmitoyltransferase-1 (CPT-1), peroxisome proliferator-activated receptor- α (PPAR-α), and phosphor-AMPK (p-AMPK). In addition, obestatin enhanced total circulatory ghrelin levels and significantly increased deacylated ghrelin to acylated ghrelin (DAG/AG) ratio. These data suggest that obestatin reverses and protects against development or progression of NAFLD directly by modulating ghrelin and adiponectin signaling or indirectly by lowering food intake.

Structure and biogenesis of ribonucleoprotein bodies in epidermal cells of Caragana arborescens L

Epidermal cells of leaf petioles, pedicles, and sepals in Caragana arborescens L. are characterized with a unique biogenesis of intracellular bodies, the presence of which continues during 10-12 days in spring, from budding till flowering and fruit inception. Initially, a nuclear body is formed as a derivative of the nucleolus at the beginning of elongation of the protodermal cells, whereas a cytoplasmic body is formed in the proximity of the nuclear envelope later. Nuclear bodies and cytoplasmic bodies do not contain DNA, lipids, and starch, and they consist of RNA tightly packaged with proteins mainly in the form of short thin fibrils with thickness of 6 nm. By the end of cell elongation and the beginning of differentiation, nuclear bodies disappear, while cytoplasmic bodies become surrounded by a homogenous zone (halo). Later, the bundles of parallel-oriented fibrils derived from the body radially pass through the homogenous zone and gradually disperse in the cytoplasm. In the differentiated epidermal cells, no traces of cytoplasmic bodies are observed; there is only one nucleolus in the nucleus. It is hypothesized that cytoplasmic bodies may function as an RNA depot, which is utilized later in cell metabolism during the formation of fruits and seeds.

Plant snRNP Biogenesis: A Perspective from the Nucleolus and Cajal Bodies

Small nuclear ribonucleoproteins (snRNPs) are protein-RNA complexes composed of specific snRNP-associated proteins along with small nuclear RNAs (snRNAs), which are non-coding RNA molecules abundant in the nucleus. snRNPs mainly function as core components of the spliceosome, the molecular machinery for pre-mRNA splicing. Thus, snRNP biogenesis is a critical issue for plants, essential for the determination of a cell's activity through the regulation of gene expression. The complex process of snRNP biogenesis is initiated by transcription of the snRNA in the nucleus, continues in the cytoplasm, and terminates back in the nucleus. Critical steps of snRNP biogenesis, such as chemical modification of the snRNA and snRNP maturation, occur in the nucleolus and its related sub-nuclear structures, Cajal bodies. In this review, I discuss roles for the nucleolus and Cajal bodies in snRNP biogenesis, and a possible linkage between the regulation of snRNP biogenesis and plant development and environmental responses.

Spatial regulation of cytoplasmic snRNP assembly at the cellular level

Small nuclear ribonucleoproteins (snRNPs) play a crucial role in pre-mRNA splicing in all eukaryotic cells. In contrast to the relatively broad knowledge on snRNP assembly within the nucleus, the spatial organization of the cytoplasmic stages of their maturation remains poorly understood. Nevertheless, sparse research indicates that, similar to the nuclear steps, the crucial processes of cytoplasmic snRNP assembly may also be strictly spatially regulated. In European larch microsporocytes, it was determined that the cytoplasmic assembly of snRNPs within a cell might occur in two distinct spatial manners, which depend on the rate of de novo snRNP formation in relation to the steady state of these particles within the nucleus. During periods of moderate expression of splicing elements, the cytoplasmic assembly of snRNPs occurred diffusely throughout the cytoplasm. Increased expression of both Sm proteins and U snRNA triggered the accumulation of these particles within distinct, non-membranous RNP-rich granules, which are referred to as snRNP-rich cytoplasmic bodies.

Transcriptional activity in diplotene larch microsporocytes, with emphasis on the diffuse stage

Manuscript provides insights into the biology of long-lived plants, different from Arabidopsis, tomato or grass species that are widely studied. In the European larch the diplotene stage lasts approximately 5 months and it is possible to divide it into several substages and to observe each of them in details. The diplotene stage is a period of intensive microsporocyte growth associated with the synthesis and accumulation of different RNA and proteins. Larch microsporocytes display changes in chromatin morphology during this stage, alternating between 4 short stages of chromatin condensation (contraction) and 5 longer diffusion (relaxation) stages. The occurrence of a diplotene diffusion stage has been observed in many plant species. Interestingly, they have also been observed during spermiogenesis and oogenesis in animals. The aim of this study was to examine whether chromatin relaxation during the diplotene is accompanied by the synthesis and maturation of mRNA. The results reveal a correlation between the diffusion and chromatin decondensation, transcriptional activity. We also found decreasing amount of poly(A) mRNA synthesis in the consecutive diffusion stages. During the early diffusion stages, mRNA is intensively synthesized. In the nuclei large amounts of RNA polymerase II, and high levels of snRNPs were observed. In the late diffusion stages, the synthesized mRNA is not directly subjected to translation but it is stored in the nucleus, and later transported to the cytoplasm and translated. In the last diffusion stage, the level of poly(A) RNA is low, but that of splicing factors is still high. It appears that the mRNA synthesized in early stages is used during the diplotene stage and is not transmitted to dyad and tetrads. In contrast, splicing factors accumulate and are most likely transmitted to the dyad and tetrads, where they are used after the resumption of intense transcription. Similar meiotic process were observed during oogenesis in animals. This indicates the existence of an evolutionarily conserved mechanism of chromatin-based regulation of gene expression during meiotic prophase I.

Lignin and lignans in plant defence: insight from expression profiling of cinnamyl alcohol dehydrogenase genes during development and following fungal infection in Populus

Cinnamyl alcohol dehydrogenase (CAD) catalyses the final step in the biosynthesis of monolignol, the main component of lignin. Lignins, deposited in the secondary cell wall, play a role in plant defence against pathogens. We re-analysed the phylogeny of CAD/CAD-like genes using sequences from recently sequenced genomes, and analysed the temporal and spatial expression profiles of CAD/CAD-like genes in Populus trichocarpa healthy and infected plants. Three fungal pathogens (Rhizoctonia solani, Fusarium oxysporum, and Cytospora sp.), varying in lifestyle and pathogenicity, were used for plant infection. Phylogenetic analyses showed that CAD/CAD-like genes were distributed in classes represented by all members from angiosperm lineages including basal angiosperms and Selaginella. The analysed genes showed different expression profiles during development and demonstrated that three genes were involved in primary xylem maturation while five may function in secondary xylem formation. Expression analysis following inoculation with fungal pathogens, showed that five genes were induced in either stem or leaves. These results add further evidence that CAD/CAD-like genes have evolved specialised functions in plant development and defence against various pest and pathogens. Two genes (PoptrCAD11 and PoptrCAD15), which were induced under various stresses, could be treated as universal markers of plant defence using lignification or lignan biosynthesis.

New insights into pioneer root xylem development: evidence obtained from Populus trichocarpa plants grown under field conditions

BACKGROUND AND AIMS

Effective programmed xylogenesis is critical to the structural framework of the plant root system and its central role in the acquisition and long-distance transport of water and nutrients. The process of xylem differentiation in pioneer roots under field conditions is poorly understood. In this study it is hypothesized that xylogenesis, an example of developmental programmed cell death (PCD), in the roots of woody plants demonstrates a clearly defined sequence of events resulting in cell death. A comprehensive analysis was therefore undertaken to identify the stages of xylogenesis in pioneer roots from procambial cells to fully functional vessels with lignified cell walls and secondary cell wall thickenings.

METHODS

Xylem differentiation was monitored in the pioneer roots of Populus trichocarpa at the cytological level using rhizotrons under field conditions. Detection and localization of the signalling molecule nitric oxide (NO) and hydrogen peroxide (H2O2) was undertaken and a detailed examination of nuclear changes during xylogenesis was conducted. In addition, analyses of the expression of genes involved in secondary cell wall synthesis were performed in situ.

KEY RESULTS

The primary event in initially differentiating tracheary elements (TEs) was a burst of NO in thin-walled cells, followed by H2O2 synthesis and the appearance of TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling)-positive nuclei. The first changes in nuclear structure were observed in the early stages of xylogenesis of pioneer roots, prior to lignification; however, the nucleus was detectable under transmission electron microscopy in differentiating cells until the stage at which vacuole integrity was maintained, indicating that their degradation was slow and prolonged. The subsequent sequence of events involved secondary cell wall formation and autophagy. Potential gene markers from the cinnamyl alcohol dehydrogenase (CAD) gene family that were related to secondary wall synthesis were associated with primary xylogenesis, showing clear expression in cells that undergo differentiation into TEs and in the thin-walled cells adjacent to the xylem pole.

CONCLUSIONS

The early events of TE formation during pioneer root development are described, together with the timing of xylogenesis from signalling via NO, through secondary cell wall synthesis and autophagy events that are initiated long before lignification. This is the first work describing experiments conducted in planta on roots under field conditions demonstrating that the process of xylogenesis in vivo might be gradual and complex.

Transcriptional activity of Hyacinthus orientalis L. female gametophyte cells before and after fertilization

We characterized three phases of Hyacinthus orientalis L. embryo sac development, in which the transcriptional activity of the cells differed using immunolocalization of incorporated 5′-bromouracil, the total RNA polymerase II pool and the hypo- (initiation) and hyperphosphorylated (elongation) forms of RNA Pol II. The first stage, which lasts from the multinuclear stage to cellularization, is a period of high transcriptional activity, probably related to the maturation of female gametophyte cells. The second stage, encompassing the period of embryo sac maturity and the progamic phase, involves the transcriptional silencing of cells that will soon undergo fusion with male gametes. During this period in the hyacinth egg cell, there are almost no newly formed transcripts, and only a small pool of RNA Pol II is present in the nucleus. The transcriptional activity of the central cell is only slightly higher than that observed in the egg cell. The post-fertilization stage is related to the transcriptional activation of the zygote and the primary endosperm cell. The rapid increase in the pool of newly formed transcripts in these cells is accompanied by an increase in the pool of RNA Pol II, and the pattern of enzyme distribution in the zygote nucleus is similar to that observed in the somatic cells of the ovule. Our data, together with the earlier results of Pięciński et al. (2008), indicate post-fertilization synthesis and the maturation of numerous mRNA transcripts, suggesting that fertilization in H. orientalis induces the activation of the zygote and endosperm genomes.

mRNA accumulation in the Cajal bodies of the diplotene larch microsporocyte

In microsporocytes of the European larch, we demonstrated the presence of several mRNAs in spherical nuclear bodies. In the nuclei of microsporocytes, we observed up to 12 bodies, ranging from 0.5 to 6 μm in diameter, during the prophase of the first meiotic division. Our previous studies revealed the presence of polyadenylated RNA (poly(A) RNA) in these bodies, but did not confirm the presence of nascent transcripts or splicing factors of the SR family. The lack of these molecules precludes the bodies from being the sites of synthesis and early maturation of primary transcripts (Kołowerzo et al., Protoplasma 236:13–19, 2009). However, the bodies serve as sites for the accumulation of splicing machinery, including the Sm proteins and small nuclear RNAs. Characteristic ultrastructures and the molecular composition of the nuclear bodies, which contain poly(A) RNA, are indicative of Cajal bodies (CBs). Here, we demonstrated the presence of several housekeeping gene transcripts—α-tubulin, pectin methylesterase, peroxidase and catalase, ATPase, and inositol-3-phosphate synthase—in CBs. Additionally, we observed transcripts of the RNA polymerase II subunits RPB2 and RPB10 RNA pol II and the core spliceosome proteins mRNA SmD1, SmD2, and SmE. The co-localization of nascent transcripts and mRNAs indicates that mRNA accumulation/storage, particularly in CBs, occurs in the nucleus of microsporocytes.

Periodic expression of Sm proteins parallels formation of nuclear Cajal bodies and cytoplasmic snRNP-rich bodies

Small nuclear ribonucleoproteins (snRNPs) play a fundamental role in pre-mRNA processing in the nucleus. The biogenesis of snRNPs involves a sequence of events that occurs in both the nucleus and cytoplasm. Despite the wealth of biochemical information about the cytoplasmic assembly of snRNPs, little is known about the spatial organization of snRNPs in the cytoplasm. In the cytoplasm of larch microsporocytes, a cyclic appearance of bodies containing small nuclear RNA (snRNA) and Sm proteins was observed during anther meiosis. We observed a correlation between the occurrence of cytoplasmic snRNP bodies, the levels of Sm proteins, and the dynamic formation of Cajal bodies. Larch microsporocytes were used for these studies. This model is characterized by natural fluctuations in the level of RNA metabolism, in which periods of high transcriptional activity are separated from periods of low transcriptional activity. In designing experiments, the authors considered the differences between the nuclear and cytoplasmic phases of snRNP maturation and generated a hypothesis about the direct participation of Sm proteins in a molecular switch triggering the formation of Cajal bodies.

Poly(A) RNA a new component of Cajal bodies

In European larch microsporocytes, spherical structures 0.5 to 6 microm in diameter are present in which poly(A) RNA accumulates. There were one to several bodies per cell and they were often present in the vicinity of the nucleolus. No nascent transcripts were observed within them. Splicing factors of the SR family, including protein SC35, which participates in bringing the 3' and 5' sites closer in the splicing reaction, were also not observed. The absence of the above-mentioned elements within bodies containing poly(A) RNA disqualifies them as sites of synthesis and preliminary stages of primary transcript maturation. However, they contained abundant elements of the splicing machinery commonly occurring in Cajal bodies, i.e., Sm proteins or small nuclear RNA (snRNA). The molecular composition as well as the characteristic ultrastructure of bodies containing poly(A) RNA proves that these were Cajal bodies. This is the first report of such poly(A) RNA localization.

Nuclear bodies in Douglas fir (Pseudotsuga menziesii Mirb.) microspores

The identification of nucleolar proteins and immunocytochemical localization of small nuclear ribonucleoprotein (snRNP) elements revealed the presence of three types of nuclear bodies in Douglas fir microspore nuclei. One type consists of structures resembling Cajal bodies (CBs) and contains nucleolar proteins as well as snRNPs and U2 snRNA. The second type is bizonal bodies, which are nuclear bodies also linked with the splicing system. The bizonal body comprises two parts: the first contains Sm proteins and stains strongly with silver stain, and the second resembles CBs in terms of the degree of silver staining and molecular composition. Douglas fir is the second species after larch where the presence of bizonal bodies has been demonstrated. Pseudotsuga menziesii Mirb and Larix decidua Mill are species with one of the longest microsporogenesis processes known in plants. The presence of bizonal bodies in both species may be linked to the intensification of the splicing processes in microspores with an exceptionally long cell cycle. The third type of structure is dense bodies, whose morphology and degree of silver staining strongly indicate their functional and spatial relationship to the dense part of bizonal bodies.

Transcriptional activity and distribution of splicing machinery elements during Hyacinthus orientalis pollen tube growth

The localization of newly formed transcripts and molecules participating in pre-mRNA splicing, i.e., small nuclear ribonucleoproteins (snRNPs) and SC35 protein, in growing pollen tubes of Hyacinthus orientalis L. were analyzed in vitro and in vivo. The results indicated that the restart of RNA synthesis occurred first in the vegetative and then in the generative nucleus of both in vitro and in vivo growing pollen tubes. Changes in RNA synthesis were accompanied by the redistribution of splicing machinery elements in both vegetative and generative nuclei of the growing pollen tube. At stages of pollen tube growth when the vegetative and generative nuclei were transcriptionally active, clear differences in the distribution pattern of the splicing system components were observed in both pollen nuclei. While both small nuclear RNA with a trimethylguanosine cap on the 5' end and SC35 protein were diffusely distributed in the nucleoplasm in the vegetative nucleus, the studied antigens were only present in the areas between condensed chromatin in the generative nucleus. When the transcriptional activity of both pollen nuclei could no longer be observed at later stages of pollen tube growth, snRNPs and SC35 protein were still present in the vegetative nuclei but not in the generative nuclei. We, therefore, investigated potential differences in the spatial organization of splicing system elements during pollen tube growth. They clearly reflect differences in gene expression patterns in the vegetative and the generative cells, which may be determined by the different biological roles of angiosperm male gametophyte cells.