The cell cycle controls spindle architecture in Arabidopsis by activating the augmin pathway.

To ensure an even segregation of chromosomes during somatic cell division, eukaryotes rely on mitotic spindles. Here, we measured prime characteristics of the Arabidopsis mitotic spindle and built a three-dimensional dynamic model using Cytosim. We identified the cell-cycle regulator CYCLIN-DEPENDENT KINASE B1 (CDKB1) together with its cyclin partner CYCB3;1 as key regulators of spindle morphology in Arabidopsis.

The phosphoinositide signature guides the final step of plant cytokinesis.

Plant cytokinesis, which fundamentally differs from that in animals, requires the outward expansion of a plasma membrane precursor named the cell plate. How the transition from a cell plate to a plasma membrane occurs remains poorly understood. Here, we report that the acquisition of plasma membrane identity occurs through lateral patterning of the phosphatidylinositol 4,5-bisphosphate PI(4,5)P at the newly formed cell plate membrane.

Large-scale analysis and computer modeling reveal hidden regularities behind variability of cell division patterns in embryogenesis.

Noise plays a major role in cellular processes and in the development of tissues and organs. Several studies have examined the origin, the integration or the accommodation of noise in gene expression, cell growth and elaboration of organ shape. By contrast, much less is known about variability in cell division plane positioning, its origin and links with cell geometry, and its impact on tissue organization.

Floral organ abscission in Arabidopsis requires the combined activities of three TALE homeodomain transcription factors.

Floral organ abscission is a separation process in which sepals, petals, and stamens detach from the plant at abscission zones. Here, we investigated the collective role of three amino-acid-loop-extension (TALE) homeobox genes ARABIDOPSIS THALIANA HOMEOBOX GENE1 (ATH1), KNAT6 (for KNOTTED LIKE from Arabidopsis thaliana) and KNAT2, which form a module that patterns boundaries under the regulation of BLADE-ON-PETIOLE 1 and 2 (BOP1/2) co-activators. These TALE homeodomain transcription factors were shown to maintain boundaries in the flower, functioning as a unit to coordinate the growth, patterning, and activity of abscission zones.

B1-type cyclins control microtubule organization during cell division in Arabidopsis.

Flowering plants contain a large number of cyclin families, each containing multiple members, most of which have not been characterized to date. Here, we analyzed the role of the B1 subclass of mitotic cyclins in cell cycle control during Arabidopsis development. While we reveal CYCB1;5 to be a pseudogene, the remaining four members were found to be expressed in dividing cells.

Quantification of Cell Division Angles in the Arabidopsis Root.

In many plant tissues, division plane orientation within cell files is highly predictable since all cells divide almost perpendicular to the cell file axis. Many mutations can affect division plane orientation, and the quantification of the deviation from the expected transverse orientation in various genetic backgrounds is thus an important issue.While several software tools have been proposed for the quantification of cellular morphology in plant tissues, none of them allowed investigating division plane orientation.

Studying Cell Division Plane Positioning in Early-Stage Embryos.

Unraveling the mechanisms that govern division plane orientation is a major challenge to understand plant development. In this respect, the Arabidopsis early embryo is a model system of choice since embryogenesis is relatively simple and cell division planes orientation is highly predictable. Here we present an integrated set of protocols to study 3D cell division patterns in early-stage Arabidopsis embryos that combine both cellular and sub-cellular localization of selected protein markers with spatial organization of cells, cytoskeleton, and nuclei.

Differential Activation of Partially Redundant Δ9 Stearoyl-ACP Desaturase Genes Is Critical for Omega-9 Monounsaturated Fatty Acid Biosynthesis During Seed Development in Arabidopsis.

The spatiotemporal pattern of deposition, final amount, and relative abundance of oleic acid (-ω-9 C18:1) and its derivatives in the different lipid fractions of the seed of Arabidopsis () indicates that omega-9 monoenes are synthesized at high rates in this organ. Accordingly, we observed that four Δ9 stearoyl-ACP desaturase (SAD)-coding genes ( [], [], , and ) are transcriptionally induced in seeds. We established that the three most highly expressed ones are directly activated by the WRINKLED1 transcription factor.

Cell geometry determines symmetric and asymmetric division plane selection in Arabidopsis early embryos.

Plant tissue architecture and organ morphogenesis rely on the proper orientation of cell divisions. Previous attempts to predict division planes from cell geometry in plants mostly focused on 2D symmetric divisions. Using the stereotyped division patterns of Arabidopsis thaliana early embryogenesis, we investigated geometrical principles underlying plane selection in symmetric and in asymmetric divisions within complex 3D cell shapes.

The preprophase band of microtubules controls the robustness of division orientation in plants.

Controlling cell division plane orientation is essential for morphogenesis in multicellular organisms. In plant cells, the future cortical division plane is marked before mitotic entry by the preprophase band (PPB). Here, we characterized an (TON1 Recruiting Motif) mutant that impairs PPB formation but does not affect interphase microtubules.

ASN1-encoded asparagine synthetase in floral organs contributes to nitrogen filling in Arabidopsis seeds.

Despite a general view that asparagine synthetase generates asparagine as an amino acid for long-distance transport of nitrogen to sink organs, its role in nitrogen metabolic pathways in floral organs during seed nitrogen filling has remained undefined. We demonstrate that the onset of pollination in Arabidopsis induces selected genes for asparagine metabolism, namely ASN1 (At3g47340), GLN2 (At5g35630), GLU1 (At5g04140), AapAT2 (At5g19950), ASPGA1 (At5g08100) and ASPGB1 (At3g16150), particularly at the ovule stage (stage 0), accompanied by enhanced asparagine synthetase protein, asparagine and total amino acids. Immunolocalization confined asparagine synthetase to the vascular cells of the silique cell wall and septum, but also to the outer and inner seed integuments, demonstrating the post-phloem transport of asparagine in these cells to developing embryos.

Studying Cell Division Plane Positioning in Early-Stage Embryos.

Unraveling the mechanisms that govern division plane orientation is a major challenge to understand plant development. In this respect, the Arabidopsis early embryo is a model system of choice since embryogenesis is relatively simple and cell division planes orientation is highly predictable. Here, we present an integrated set of protocols to study 3D cell division patterns in early-stage Arabidopsis embryos that combine both cellular and sub-cellular localization of selected protein markers with spatial organization of cells, cytoskeleton, and nuclei.

A conserved role for CUP-SHAPED COTYLEDON genes during ovule development.

The evolution of plant reproductive strategies has led to a remarkable diversity of structures, especially within the flower, a structure characteristic of the angiosperms. In flowering plants, sexual reproduction depends notably on the development of the gynoecium that produces and protects the ovules. In Arabidopsis thaliana, ovule initiation is promoted by the concerted action of auxin with CUC1 (CUP-SHAPED COTYLEDON1) and CUC2, two genes that encode transcription factors of the NAC family (NAM/ATAF1,2/CUC).

Disruption of the CYTOCHROME C OXIDASE DEFICIENT1 gene leads to cytochrome c oxidase depletion and reorchestrated respiratory metabolism in Arabidopsis.

Cytochrome c oxidase is the last respiratory complex of the electron transfer chain in mitochondria and is responsible for transferring electrons to oxygen, the final acceptor, in the classical respiratory pathway. The essentiality of this step makes it that depletion in complex IV leads to lethality, thereby impeding studies on complex IV assembly and respiration plasticity in plants. Here, we characterized Arabidopsis (Arabidopsis thaliana) embryo-lethal mutant lines impaired in the expression of the CYTOCHROME C OXIDASE DEFICIENT1 (COD1) gene, which encodes a mitochondria-localized PentatricoPeptide Repeat protein.

Independent and interactive effects of DOF affecting germination 1 (DAG1) and the Della proteins GA insensitive (GAI) and Repressor of ga1-3 (RGA) in embryo development and seed germination.

Background: The transcription factor DOF AFFECTING GERMINATION1 (DAG1) is a repressor of seed germination acting downstream of the master repressor PHYTOCROME INTERACTING FACTOR3-LIKE 5 (PIL5). Among others, PIL5 induces the expression of the genes encoding the two DELLA proteins GA INSENSITIVE 1 (GAI) and REPRESSOR OF ga1-3 (RGA).

Results: Based on the properties of gai-t6 and rga28 mutant seeds, we show here that the absence of RGA severely increases dormancy, while lack of GAI only partially compensates RGA inactivation.

Strigolactones inhibit caulonema elongation and cell division in the moss Physcomitrella patens.

In vascular plants, strigolactones (SLs) are known for their hormonal role and for their role as signal molecules in the rhizosphere. SLs are also produced by the moss Physcomitrella patens, in which they act as signaling factors for controlling filament extension and possibly interaction with neighboring individuals. To gain a better understanding of SL action at the cellular level, we investigated the effect of exogenously added molecules (SLs or analogs) in moss growth media.

Spatio-temporal analysis of cellulose synthesis during cell plate formation in Arabidopsis.

During cytokinesis a new crosswall is rapidly laid down. This process involves the formation at the cell equator of a tubulo-vesicular membrane network (TVN). This TVN evolves into a tubular network (TN) and a planar fenestrated sheet, which extends at its periphery before fusing to the mother cell wall.

A galactosyltransferase acting on arabinogalactan protein glycans is essential for embryo development in Arabidopsis.

Arabinogalactan proteins (AGPs) are a complex family of cell-wall proteoglycans that are thought to play major roles in plant growth and development. Genetic approaches to studying AGP function have met limited success so far, presumably due to redundancy within the large gene families encoding AGP backbones. Here we used an alternative approach for genetic dissection of the role of AGPs in development by modifying their glycan side chains.

A protein phosphatase 2A complex spatially controls plant cell division.

In the absence of cell migration, the orientation of cell divisions is crucial for body plan determination in plants. The position of the division plane in plant cells is set up premitotically via a transient cytoskeletal array, the preprophase band, which precisely delineates the cortical plane of division. Here we describe a protein complex that targets protein phosphatase 2A activity to microtubules, regulating the transition from the interphase to the premitotic microtubule array.

OCTOPUS, a polarly localised membrane-associated protein, regulates phloem differentiation entry in Arabidopsis thaliana.

Vascular development is embedded into the developmental context of plant organ differentiation and can be divided into the consecutive phases of vascular patterning and differentiation of specific vascular cell types (phloem and xylem). To date, only very few genetic determinants of phloem development are known. Here, we identify OCTOPUS (OPS) as a potentiator of phloem differentiation.

The transcription factor BELLRINGER modulates phyllotaxis by regulating the expression of a pectin methylesterase in Arabidopsis.

Plant leaves and flowers are positioned along the stem in a regular pattern. This pattern, which is referred to as phyllotaxis, is generated through the precise emergence of lateral organs and is controlled by gradients of the plant hormone auxin. This pattern is actively maintained during stem growth through controlled cell proliferation and elongation.

Sphingolipids containing very-long-chain fatty acids define a secretory pathway for specific polar plasma membrane protein targeting in Arabidopsis.

Sphingolipids are a class of structural membrane lipids involved in membrane trafficking and cell polarity. Functional analysis of the ceramide synthase family in Arabidopsis thaliana demonstrates the existence of two activities selective for the length of the acyl chains. Very-long-acyl-chain (C > 18 carbons) but not long-chain sphingolipids are essential for plant development.

The function of TONNEAU1 in moss reveals ancient mechanisms of division plane specification and cell elongation in land plants.

The preprophase band (PPB) is a transient ring of microtubules that forms before mitosis in land plants, and delineates the cytokinetic division plane established at telophase. It is one of the few derived traits specific to embryophytes, in which it is involved in the spatial control of cell division. Here we show that loss of function of Physcomitrella patens PpTON1 strongly affects development of the moss gametophore, phenocopying the developmental syndrome observed in Arabidopsis ton1 mutants: mutant leafy shoots display random orientation of cell division and severe defects in cell elongation, which are correlated with absence of PPB formation and disorganization of the cortical microtubule array in interphase cells.

The Arabidopsis BLAP75/Rmi1 homologue plays crucial roles in meiotic double-strand break repair.

In human cells and in Saccharomyces cerevisiae, BLAP75/Rmi1 acts together with BLM/Sgs1 and TopoIIIalpha/Top3 to maintain genome stability by limiting crossover (CO) formation in favour of NCO events, probably through the dissolution of double Holliday junction intermediates (dHJ). So far, very limited data is available on the involvement of these complexes in meiotic DNA repair. In this paper, we present the first meiotic study of a member of the BLAP75 family through characterisation of the Arabidopsis thaliana homologue.

Reciprocal chromosome translocation associated with TDNA-insertion mutation in Arabidopsis: genetic and cytological analyses of consequences for gametophyte development and for construction of doubly mutant lines.

Chromosomal rearrangements may complicate construction of Arabidopsis with multiple TDNA-insertion mutations. Here, crossing two lines homozygous for insertions in AtREV3 and AtPOLH (chromosomes I and V, respectively) and selfing F1 plants yielded non-Mendelian F2 genotype distributions: frequencies of +/++/+ and 1/1 2/2 progeny were only 0.42 and 0.