Physiological and transcriptomic evidence for a close coupling between chloroplast ontogeny and cell cycle progression in the pennate diatom Seminavis robusta

Despite the growing interest in diatom genomics, detailed time series of gene expression in relation to key cellular processes are still lacking. Here, we investigated the relationships between the cell cycle and chloroplast development in the pennate diatom Seminavis robusta. This diatom possesses two chloroplasts with a well-orchestrated developmental cycle, common to many pennate diatoms. By assessing the effects of induced cell cycle arrest with microscopy and flow cytometry, we found that division and reorganization of the chloroplasts are initiated only after S-phase progression. Next, we quantified the expression of the S. robusta FtsZ homolog to address the division status of chloroplasts during synchronized growth and monitored microscopically their dynamics in relation to nuclear division and silicon deposition. We show that chloroplasts divide and relocate during the S/G2 phase, after which a girdle band is deposited to accommodate cell growth. Synchronized cultures of two genotypes were subsequently used for a cDNA-amplified fragment length polymorphism-based genome-wide transcript profiling, in which 917 reproducibly modulated transcripts were identified. We observed that genes involved in pigment biosynthesis and coding for light-harvesting proteins were up-regulated during G2/M phase and cell separation. Light and cell cycle progression were both found to affect fucoxanthin-chlorophyll a/c-binding protein expression and accumulation of fucoxanthin cell content. Because chloroplasts elongate at the stage of cytokinesis, cell cycle-modulated photosynthetic gene expression and synthesis of pigments in concert with cell division might balance chloroplast growth, which confirms that chloroplast biogenesis in S. robusta is tightly regulated

Transcriptional analysis of cell growth and morphogenesis in the unicellular green alga Micrasterias (Streptophyta), with emphasis on the role of expansin

<p>Abstract</p> <p>Background</p> <p>Streptophyte green algae share several characteristics of cell growth and cell wall formation with their relatives, the embryophytic land plants. The multilobed cell wall of <it>Micrasterias denticulata </it>that rebuilds symmetrically after cell division and consists of pectin and cellulose, makes this unicellular streptophyte alga an interesting model system to study the molecular controls on cell shape and cell wall formation in green plants.</p> <p>Results</p> <p>Genome-wide transcript expression profiling of synchronously growing cells identified 107 genes of which the expression correlated with the growth phase. Four transcripts showed high similarity to expansins that had not been examined previously in green algae. Phylogenetic analysis suggests that these genes are most closely related to the plant EXPANSIN A family, although their domain organization is very divergent. A GFP-tagged version of the expansin-resembling protein MdEXP2 localized to the cell wall and in Golgi-derived vesicles. Overexpression phenotypes ranged from lobe elongation to loss of growth polarity and planarity. These results indicate that MdEXP2 can alter the cell wall structure and, thus, might have a function related to that of land plant expansins during cell morphogenesis.</p> <p>Conclusions</p> <p>Our study demonstrates the potential of <it>M. denticulata </it>as a unicellular model system, in which cell growth mechanisms have been discovered similar to those in land plants. Additionally, evidence is provided that the evolutionary origins of many cell wall components and regulatory genes in embryophytes precede the colonization of land.</p

Cell growth and morphogenesis in the desmid Micrasterias denticulata (Zygnemophyceae, Streptophyta) through transcriptomics and reverse genetics

This thesis addresses a fundamental biological question: how is plant cell morphology achieved? The shape of a plant cell inherently defines its function, for both unicellular algae and cells associated in a tissue. Since the latter are difficult to examine individually, a unicellular representative was found in the streptophyte green alga Micrasterias denticulata Bréb. Being their closest unicellular relative and having a cell wall with similar constituents, Micrasterias bears close resemblance to land plants. For decades, its haploid constitution, large size and, above all, complex morphology and distinct growth mechanism have been recognized as trumps for research on spatial and temporal patterning of cell wall biogenesis. The aim of this thesis is to identify and describe molecular mechanisms governing cell pattern and cell wall formation during Micrasterias cell growth. Since this is the first molecular-genetic investigation of Micrasterias, several challenges had to be taken up. The strategy of the project is based on the cDNA-AFLP (cDNA-Amplified Fragment Length Polymorphism) technique (Vuylsteke et al., 2007), which allows quantitative gene expression profiling under differential cellular conditions without prior sequence knowledge. Through cDNA-AFLP analysis (new) genes involved in a particular physiological process, in casu cell growth and morphogenesis, can be identified. Knowledge about the expression of a collection of co-regulated genes, resulting from the cDNA-AFLP analysis, allows setting up hypotheses about their function. In order to be able to functionally study presumed key regulatory genes by means of reverse genetics, a genetic transformation protocol had to be established. Despite the transiency of the transformation, transgenic cell lines served subcellular localization studies of tagged proteins and/or gene overexpression phenotyping, thus providing a first step towards their functional characterization

Groen van toen : de verdwenen flora van Oost-Vlaanderen

Begin 19e eeuw verzamelde de botanicus Charles van Hoorebeke ruim duizend plantensoorten. Met zijn herbarium beschikt Oost-Vlaanderen als enige Belgische provincie over een volledige historische catalogus van wilde flora van vóór de industriële en agrarische revolutie. En wat blijkt? 133 soorten, met prachtige namen als zevenster, fijn goudscherm, genadekruid en rozenkransje, zijn er intussen verdwenen. Hoe is het zover kunnen komen en wat kunnen we eraan doen? Dit boek brengt het verhaal van de verdwenen plantensoorten en de landschapselementen waarin ze voorkwamen vanuit een ecologisch en historisch perspectief. Het is geschreven voor iedereen met een interesse in planten of het behoud van biodiversiteit

Florient - a database dealing with historic wild plant occurrences

Florient - a database dealing with historic wild plant occurrences is an occurrence dataset published by Ghent University and the Belgian Biodiversity Platform. The FLORIENT database is based on the herbarium of Charles Van Hoorebeke (1790-1821), in which he recorded nearly all wild plants that occurred in the province of East Flanders. A prospectus of his planned publication about this, the "Flore de la Flandre Orientale", appeared in 1821. That same year he died. As a result of which his work never appeared in print and the data were not available. Frans Roucel (1765-1831), a contemporary from Aalst, focused in his published floras (from 1792 and 1803) on rare wild plants and their use, and went into more detail about the growing conditions of the species. The combination of information from both works provides an exceptionally complete and detailed picture of the flora of East Flanders around the beginning of the 19th century, before the industrial and agricultural revolution. The digital collection is also available at www.botanicalcollections.be This dataset contains historic wild plant occurrences (early 19th century). Here it is published as a standardized Darwin Core Archive and includes for each record an eventID, date, location, sampling protocol, occurrenceID, the number of recorded individuals, status (present/absent), . Issues with the dataset can be reported at https://github.com/BelgianBiodiversityPlatform/data-publication-bbpf/tree/main/datasets/florient-occurrences Generalized and/or withheld information: as these are historic occurrences, the location is geocoded to the municipality as it originally appeared in the data. We have released this dataset to the public domain under a Creative Commons Zero waiver. We would appreciate it if you follow the INBO norms for data use (https://www.inbo.be/en/norms-data-use) when using the data. If you have any questions regarding this dataset, don't hesitate to contact us via the contact information provided in the metadata

SHUGOSHINs and PATRONUS protect meiotic centromere cohesion in Arabidopsis thaliana

In meiosis, chromosome cohesion is maintained by the cohesin complex, which is released in a two-step manner. At meiosis I, the meiosis-specific cohesin subunit Rec8 is cleaved by the protease Separase along chromosome arms, allowing homologous chromosome segregation. Next, in meiosis II, cleavage of the remaining centromere cohesin results in separation of the sister chromatids. In eukaryotes, protection of centromeric cohesion in meiosis I is mediated by SHUGOSHINs (SGOs). The Arabidopsis genome contains two SGO homologs. Here we demonstrate that Atsgo1 mutants show a premature loss of cohesion of sister chromatid centromeres at anaphase I and that AtSGO2 partially rescues this loss of cohesion. In addition to SGOs, we characterize PATRONUS which is specifically required for the maintenance of cohesion of sister chromatid centromeres in meiosis II. In contrast to the Atsgo1 Atsgo2 double mutant, patronus T-DNA insertion mutants only display loss of sister chromatid cohesion after meiosis I, and additionally show disorganized spindles, resulting in defects in chromosome segregation in meiosis. This leads to reduced fertility and aneuploid offspring. Furthermore, we detect aneuploidy in sporophytic tissue, indicating a role for PATRONUS in chromosome segregation in somatic cells. Thus, ploidy stability is preserved in Arabidopsis by PATRONUS during both meiosis and mitosis.status: publishe

SHUGOSHINs and PATRONUS protect meiotic centromere cohesion in Arabidopsis thaliana

In meiosis, chromosome cohesion is maintained by the cohesin complex, which is released in a two-step manner. At meiosis I, the meiosis-specific cohesin subunit Rec8 is cleaved by the protease Separase along chromosome arms, allowing homologous chromosome segregation. Next, in meiosis II, cleavage of the remaining centromere cohesin results in separation of the sister chromatids. In eukaryotes, protection of centromeric cohesion in meiosis I is mediated by SHUGOSHINs (SGOs). The Arabidopsis genome contains two SGO homologs. Here we demonstrate that Atsgo1 mutants show a premature loss of cohesion of sister chromatid centromeres at anaphase I and that AtSGO2 partially rescues this loss of cohesion. In addition to SGOs, we characterize PATRONUS which is specifically required for the maintenance of cohesion of sister chromatid centromeres in meiosis II. In contrast to the Atsgo1 Atsgo2 double mutant, patronus T-DNA insertion mutants only display loss of sister chromatid cohesion after meiosis I, and additionally show disorganized spindles, resulting in defects in chromosome segregation in meiosis. This leads to reduced fertility and aneuploid offspring. Furthermore, we detect aneuploidy in sporophytic tissue, indicating a role for PATRONUS in chromosome segregation in somatic cells. Thus, ploidy stability is preserved in Arabidopsis by PATRONUS during both meiosis and mitosis