Littérature scientifique sur le sujet « Cell cycle, MOB protein, development, Arabidopsis thaliana »

Abstract SAMBA has been identified as a plant-specific regulator of the anaphase-promoting complex/cyclosome (APC/C) that controls unidirectional cell cycle progression in Arabidopsis (Arabidopsis thaliana), but so far its role has not been studied in monocots. Here, we show the association of SAMBA with the APC/C is conserved in maize (Zea mays). Two samba genome edited mutants showed growth defects, such as reduced internode length, shortened upper leaves with erect leaf architecture, and reduced leaf size due to an altered cell division rate and cell expansion, which aggravated with plant age. The two mutants differed in the severity and developmental onset of the phenotypes, because samba-1 represented a knockout allele, while translation re-initiation in samba-3 resulted in a truncated protein that was still able to interact with the APC/C and regulate its function, albeit with altered APC/C activity and efficiency. Our data are consistent with a dosage-dependent role for SAMBA to control developmental processes for which a change in growth rate is pivotal.

Expression of the Arabidopsis thaliana gene PROLIFERA (PRL) was examined during development of root-knot and cyst nematode feeding sites. These obligate plant parasites establish specialized feeding structures in roots that allow them to withdraw nutrients from the host. In the process of establishing feeding sites, nematodes alter cell cycle regulation. PRL is normally expressed specifically in dividing cells at all stages of plant development and was used here as a marker for cell division. PRL expression, reported from a PRL∷GUS fusion protein, was detected in nematode feeding sites of both root-knot and cyst nematodes from the earliest stages of infection in both giant cells and syncytia. However, unlike other cell cycle genes, expression of PRL was detected only occasionally in cells surrounding the feeding sites. PRL∷GUS activity persisted until late in the infection cycle, past the time when other cell cycle genes are expressed. These data indicate that some aspects of the PRL expression pattern during nematode infection differ from that of other cell cycle genes.

Chloroplast biogenesis involves the coordinated expression of the plastid and nuclear genomes, requiring information to be sent from the nucleus to the developing chloroplasts and vice versa. Although it is well known how the nucleus controls chloroplast development, it is still poorly understood how the plastid communicates with the nucleus. Currently, haem is proposed as a plastid-to-nucleus (retrograde) signal that is involved in various physiological regulations, such as photosynthesis-associated nuclear genes expression and cell cycle in plants and algae. However, components that transduce haem-dependent signalling are still unidentified. In this study, by using haem-immobilized high-performance affinity beads, we performed proteomic analysis of haem-binding proteins from Arabidopsis thaliana and Cyanidioschyzon merolae . Most of the identified proteins were non-canonical haemoproteins localized in various organelles. Interestingly, half of the identified proteins were nucleus proteins, some of them have a similar function or localization in either or both organisms. Following biochemical analysis of selective proteins demonstrated haem binding. This study firstly demonstrates that nucleus proteins in plant and algae show haem-binding properties. This article is part of the theme issue ‘Retrograde signalling from endosymbiotic organelles’.

Abstract The ataxia-telangiectasia mutated (ATM) and ATM and Rad3-related (ATR) kinases coordinate the DNA damage response. The roles described for Arabidopsis thaliana ATR and ATM are assumed to be conserved over other plant species, but molecular evidence is scarce. Here, we demonstrate that the functions of ATR and ATM are only partially conserved between Arabidopsis and maize (Zea mays). In both species, ATR and ATM play a key role in DNA repair and cell cycle checkpoint activation, but whereas Arabidopsis plants do not suffer from the absence of ATR under control growth conditions, maize mutant plants accumulate replication defects, likely due to their large genome size. Moreover, contrarily to Arabidopsis, maize ATM deficiency does not trigger meiotic defects, whereas the ATR kinase appears to be crucial for the maternal fertility. Strikingly, ATR is required to repress premature endocycle onset and cell death in the maize endosperm. Its absence results in a reduction of kernel size, protein and starch content, and a stochastic death of kernels, a process being counteracted by ATM. Additionally, while Arabidopsis atr atm double mutants are viable, no such mutants could be obtained for maize. Therefore, our data highlight that the mechanisms maintaining genome integrity may be more important for vegetative and reproductive development than previously anticipated.

The SWR1 complex (SWR1-C) is important for the deposition of histone variant H2A.Z into chromatin to regulate gene expression. Characterization of SWR1-C subunits in Arabidopsis thaliana has revealed their role in variety of developmental processes. Oryza sativa actin related protein 6 (OsARP6) is a subunit of rice SWR1-C. Its role in rice plant development is unknown. Here, we examined the subcellular localization, expression patterns, and loss of function phenotypes for this protein and found that OsARP6 is a nuclear localized protein, and is broadly expressed. OsARP6 interacted with OsPIE1, a central ATPase subunit of rice SWR1-C. The osarp6 knockout mutants displayed pleiotropic phenotypic alterations in vegetative and reproductive traits, including semi-dwarf phenotype, lower tillers number, short leaf length, changes in spikelet morphology, and seed abortion. Microscopic thin sectioning of the top internode revealed that the dwarf phenotype of osarp6 was due to reduced number of cells rather than reduced cell length. The altered transcript level of genes involved in cell division suggested that OsARP6 affects cell cycle regulation. In addition, H2A.Z levels were reduced at the promoters and transcription start sites (TSS) of the regulated genes in osarp6 plants. Together, these results suggest that OsARP6 is involved in rice plant development, and H2A.Z deposition.

The root system of the plant is essential for taking up water and nutrients, serves as an anchor and is the organ where plant-microorganism interaction takes place. When the Plant Growth Promoting Rhizobacteria (PGPR) Azospirillum brasilense Sp245 colonizes the root of the plants, it halts the growth of the primary root and stimulates the development of the lateral roots and root hairs which support vegetative, green biomass. Target of Rapamycin (TOR) is a highly conserved protein in all eukaryotes, and it controls anabolic processes, such as cell cycle, ribosome biogenesis, protein synthesis, cell wall changes and photosynthesis among others. TOR in plants forms part of the TORC1 complex, which when is activated by auxins and light, activates anabolic processes and represses autophagy. TOR regulates the growth of the primary root of Arabidopsis through cell proliferation and elongation. In the present investigation, the participation of TOR during the Arabidopsis-Azospirillum interaction was determined using two approaches, a pharmacology and other genetic. The results showed that TOR is involved in the development of the lateral roots of A. thaliana seedlings inoculated with A. brasilense.

We have used whole mount immunofluorescence labelling with the antibody 4G3, raised against the human snRNP-specific protein U2B″, and whole mount in situ hybridization with an anti-sense probe to a conserved region of U2 snRNA, in combination with confocal microscopy, to examine the organization of spliceosomal components throughout the development of the Arabidopsis thaliana root epidermis. We show that the number of coiled bodies, nuclear organelles in which splicing snRNPs and snRNAs concentrate, is developmentally regulated in the Arabidopsis root epidermis. Firstly, there is a progression from a small number of coiled bodies in the quiescent centre and initial cells, to a larger number in the cell division zone, returning to a lower number in the cell elongation and differentiation zone. Secondly, trichoblasts (root-hair forming epidermal cells) have on average 1.5 times more and often smaller coiled bodies than atrichoblasts (hairless epidermal cells). Moreover, we have shown that these differences in coiled body numbers are related to differences in cell cycle stage, cell type and developmental stage, but are not due to differences in nucleolar or general metabolic activity per se. We discuss possible explanations, including a model in which coiled bodies coalesce during interphase, for the developmental dynamics of coiled bodies.

Nuclear tRNA export plays an essential role in several key cellular processes, such as regulation of protein synthesis, cell cycle progression, response to nutrient availability and DNA damage, and development. While the overall mechanism of nuclear tRNA export is, in general, poorly understood, the details of specific steps are emerging from studies conducted in different organisms aimed at identifying and characterizing components involved in the process. Here, we report that Arabidopsis thaliana (L.) Heynh At2g40730 encodes CTEXP, a cytoplasmic protein component of the nuclear tRNA export process. CTEXP bound tRNA directly and saturably, and like the nuclear tRNA export receptor PAUSED, overexpression of CTEXP restored export of a nuclear export-defective lysine amber suppressor tRNA in tobacco cells. CTEXP was also found to associate with nucleoporins of the nuclear pore complex (NPC), PAUSED, and the GTPase Ran in vivo. CTEXP interacted directly with PAUSED in vitro and RanGTP, but not RanGDP. Furthermore, a portion of CTEXP appeared to associate with the NPC. Taken together, the data suggest that CTEXP assists with unloading of tRNAs from PAUSED at the cytoplasmic side of the NPC in plant cells.

The ubiquitin E3 ligase BIG BROTHER/ENHANCER OF DA1 (BB) gene encoding a RING finger protein was identified as a central growth regulator in Arabidopsis thaliana. It was found that BB restricts cell proliferation and promotes leaf senescence. Besides of Arabidopsis, however, the role and regulation of BB in other plant species is only sparsely known. Supposing that the BB gene, like in Arabidopsis, has an important role in the development of potato we aimed to analyse a 3.0-kb promoter sequence of the potato BB gene, StBB, in silico and study the level of StBB expression by quantitative reverse transcription PCR in different organs. A total of 48 binding sites for 15 transcription factor (TF) families were predicted. Most of them were located in the -1.5-kb promoter region. The dominating family of TFs was DOF. It was found that 20 out of the 24 TFs with known functions are involved in developmental processes such as for example, the flower-, leaf-, stem- and root development or cell cycle regulation. In line with this finding, the StBB mRNA was detected in each organ tested with the largest amounts in petal and stamen. These results suggest a similar function of StBB in potato than that is of BB in Arabidopsis, i.e., restriction of organ overgrowth during development and limitation of the plant growth.

Katanin, is a microtubule severing protein that orchestrates microtubule organization throughout the plant cell cycle. Taking into consideration the role of the microtubule cytoskeleton in the stomatal development, the Arabidopsis thaliana katanin mutants, fra2, lue1 and bot1 were studied to observe how the absence of function of/malfunction of katanin affects stomatal development. Katanin mutants are characterised by less mature stomata and more young stomata and meristemoids forming clusters. The size of the mature stomata differed from col-0, with the katanin mutants having shorter guard cells and pores as well as smaller pore aperture. In addition, a unique type of cell was observed in the fra2 mutant, the persistent guard mother cells (GMC’s), where the GMC persisted and did not divide symmetrically to form a stoma. Another rather significant observation was that the cell walls of some epidermal cells in the mutants appeared to be incomplete. As far as the cell wall matrix components distribution is concerned, callose did not display significant differences compared to col-0 while pectins and hemicelluloses were differentially dispersed. Microtubules in cytokinetic GMCs were long, bended and connected to the nuclei, while microtubule arrays in katanin mutant leaf epidermis were aberrant and stomatal complexes had astral microtubule arrays as it was observed in the wild type. In conclusion, the malfunction of katanin appears to affect the development of stomata in the epidermis of young leaves in Arabidopsis thaliana, affecting not only stomatal patterning, since the one-cell spacing rule was compromised, but also the morphology of the stomatal complexes. The cell wall-matrix appears altered in the katanin mutants, possibly affecting the function of the stomata since katanin mutant stomata had a reduced pore aperture.

The MOBs (Mps1-One Binder) family is a group of cell cycle-associated, non-catalytic proteins highly conserved in eukaryotes, whose founding members are implicated in mitotic exit and coordination of cell polarity with cell cycle progression. Mob1 proteins have been demonstrated to be important for both mitosis completion and cell plate formation in yeast. In particular, in Saccharomyces cerevisiae Mob1p is an essential regulator of the localization and activity of Dbf2 protein kinase, a component of the mitotic exit network (MEN). MEN components were also found in the higher eukaryotes, indeed Mob1 and Dbf2-related proteins (NDR – nuclear Dbf2 related) have been found in animal cell suggesting that their role might be conserved through evolution. Members of the NDR family are essential components of pathways that control important cellular processes, such as mitotic exit, cytokinesis, cell proliferation and morphogenesis, and apoptosis. In plants, MOB1-like proteins were studied only in Medicago sativa, where they are expressed in a cell cycle-dependent manner and are localized in the cell division midplane during cytokinesis. In this plant Mob1-like transcripts and proteins seem also to be associated with the onset of programmed cell death. The aim of this thesis was to better understand the role of MOB-like proteins in plants. Using Arabidopsis thaliana as a model organism, we have pursued two main aims: the development and characterization of transgenic lines with altered expression of Mob-like genes and the identification of plant Dbf2-related protein/s. In conclusion we have demonstrated the importance of the MOB-A protein in Arabidopsis thaliana growth and development. Specifically we showed that the reduction of Mob-A level affects cell morphology, cell size and cell proliferation in root tip, the regular progression of megasporogenesis and the formation of functional embryo sacs in reproductive organs. The whole results seem to indicate that Mob-A has more than one role in plant growth and development. Given the complexity of the interactions it is possible that MOB-A belongs to specific networks depending on the interactor and/or that the activation of different pathways is organism, tissue and/or cellular context dependent. It is also likely that different isoforms of MOB-like proteins belonging to different pathways can substitute each other, making mutant analysis more complex. However the future identification of their binding partners may shed light in determining the functions of these proteins.

TCTP (Translationally Controlled Tumor Protein) est une protéine très conservée chez l'ensemble des eucaryotes. C’est une protéine vitale impliquée dans divers processus essentiels, et pour de nombreux organismes son absence conduit à la létalité dès les stades embryonnaires.Chez les animaux comme chez les végétaux, TCTP joue un rôle primordial dans la croissance et le développement des individus. En plus de son implication dans l’apoptose et la réparation de l’ADN, TCTP favorise la prolifération cellulaire, et se trouve donc être un élément important de la tumorigenèse. Chez les végétaux, la forte conservation de TCTP a permis la préservation de la plupart des fonctions décrites chez les animaux, mais les facteurs qui interviennent en amont ne sont pas encore connus.Par la mise en place, la conduite et la finalisation de deux cribles génétiques utilisant la plante modèle Arabidopsis thaliana, ce travail de thèse a cherché à identifier des facteurs situés en amont de TCTP. En parallèle, une seconde étude fut menée afin de mesurer l'impact de l'absence de TCTP sur les voies de l’auxine et des cytokinines au cours du développement embryonnaire, permettant de mieux comprendre l’origine de l’embryolétalité du mutant tctp
TCTP (Translationally Controlled Tumor Protein) is strongly conserved among eukaryotes. It is a vital protein implicated in various major processes, and its absence leads to early embryolethality in many organisms. In plants as in animals, TCTP is a key factor of growth and development. Implicated in apoptosis and DNA repair, TCTP is also an enhancer of cell proliferation, and is a key element of tumorigenesis. Major functions of TCTP are conserved between plants and animals, but upstream factors are not known yet. Using a genetic screen on the model plant Arabidopsis thaliana, the principal goal of this thesis was to discover regulators of TCTP.In parallel, the impact of TCTP knockout on auxin and cytokinin pathways during embryo development was investigated

Genetic and biochemical analysis of glucosinolate breakdown: The effects of indole-3-carbinol on plant physiology and development Glucosinolates are a class of defense-related secondary metabolites found in all crucifers, including important oilseed and vegetable crops in the Brassica genus and the well-studied model plant Arabidopsis thaliana. Upon tissue damage, such as that provided by insect feeding, glucosinolates are subjected to catalysis and spontaneous degradation to form a variety of breakdown products. These breakdown products typically have a deterrent effect on generalist herbivores. Glucosinolate breakdown products also contribute to the anti-carcinogenic effects of eating cabbage, broccoli and related cruciferous vegetables. Indole-3-carbinol, a breakdown product of indol-3-ylmethylglucosinolate, forms conjugates with several other plant metabolites. Although some indole-3-carbinol conjugates have known functions in defense against herbivores and pathogens, most play as yet unidentified roles in plant metabolism, and possibly also plant development. At the outset, our proposal had three main hypotheses: (1) There is a specific detoxification pathway for indole-3-carbinol; (2) Metabolites derived from indole-3-carbinol are phloem-mobile and serve as signaling molecules; and (3) Indole-3-carbinol affects plant cell cycle and cell-differentiation pathways. The experiments were designed to enable us to elucidate how indole-3-carbinol and related metabolites affect plants and their interactions with herbivorous insects. We discovered that indole-3- carbinol rapidly and reversibly inhibits root elongation in a dose-dependent manner, and that this inhibition is accompanied by a loss of auxin activity in the root meristem. A direct interaction between indole-3-carbinol and the auxin perception machinery was suggested, as application of indole-3-carbinol rescued auxin-induced root phenotypes. In vitro and yeast-based protein interaction studies showed that indole-3-carbinol perturbs the auxin-dependent interaction of TIR1 with Aux/IAA proteins, supporting the notion that indole-3-carbinol acts as an auxin antagonist. Furthermore, transcript profiling experiments revealed the influence of indole-3-carbinol on auxin signaling in root tips, and indole-3-carbinol also affected auxin transporters. Brief treatment with indole-3-carbinol led to a reduction in the amount of PIN1 and to mislocalization of PIN2. The results indicate that chemicals induced by herbivory, such as indole-3-carbinol, function not only to repel herbivores, but also as signaling molecules that directly compete with auxin to fine tune plant growth and development, which implies transport of indole-3- carbinol that we are as yet unsuccessful in detecting. Our results indicate that plant defensive metabolites also have secondary functions in regulating aspects of plant metabolism, thereby providing diversity in defense-related plant signaling pathways. Such diversity of of signaling by defensive metabolites would be beneficial for the plant, as herbivores and pathogens would be less likely to mount effective countermeasures. We propose that growth arrest can be mediated directly by the herbivory-induced chemicals, in our case, indole-3-carbinol. Thus, glucosinolate breakdown to I3C following herbivory would have two outcomes: (1) Indole-3-carbinaol would inhibit the herbivore, while (2) at the same time inducing growth arrest within the plant. Thus, our results indicate that I3C is a defensive phytohormone that modulates auxin signaling, leading to growth arrest.