Transcriptional Regulation of Ribosome Components Are Determined by Stress According to Cellular Compartments in Arabidopsis thaliana

Plants have to coordinate eukaryotic ribosomes (cytoribosomes) and prokaryotic ribosomes (plastoribosomes and mitoribosomes) production to balance cellular protein synthesis in response to environmental variations. We identified 429 genes encoding potential ribosomal proteins (RP) in Arabidopsis thaliana. Because cytoribosome proteins are encoded by small nuclear gene families, plastid RP by nuclear and plastid genes and mitochondrial RP by nuclear and mitochondrial genes, several transcriptional pathways were attempted to control ribosome amounts. Examining two independent genomic expression datasets, we found two groups of RP genes showing very different and specific expression patterns in response to environmental stress. The first group represents the nuclear genes coding for plastid RP whereas the second group is composed of a subset of cytoribosome genes coding for RP isoforms. By contrast, the other cytoribosome genes and mitochondrial RP genes show less constraint in their response to stress conditions. The two subsets of cytoribosome genes code for different RP isoforms. During stress, the response of the intensively regulated subset leads to dramatic variation in ribosome diversity. Most of RP genes have same promoter structure with two motifs at conserved positions. The stress-response of the nuclear genes coding plastid RP is related with the absence of an interstitial telomere motif known as telo box in their promoters. We proposed a model for the “ribosome code” that influences the ribosome biogenesis by three main transcriptional pathways. The first pathway controls the basal program of cytoribosome and mitoribosome biogenesis. The second pathway involves a subset of cytoRP genes that are co-regulated under stress condition. The third independent pathway is devoted to the control of plastoribosome biosynthesis by regulating both nuclear and plastid genes

Senescence and death of plant organs: Nutrient recycling and developmental regulation

Senescence and programmed cell death are important features for plant development. By allowing nutrient recycling and reallocation all along plant life, senescence contributes to the plant survival and the developmental program. This review first presents the concept of senescence in the global whole-plant life story, with an emphasis on the control exerted by flowering. It then focuses on leaf-senescence and its control by hormones, nutrients and development. The role of autophagy and of the Target of Rapamycin (TOR) kinase as potential regulators integrating environmental and endogenous signals, which control cell proliferation, reprogramming and nutrient management, is finally considered.L’idée que la sénescence végétale ainsi que la mort cellulaire sont programmées et contrôlées par des facteurs endogènes est relativement récente. Cette revue discute, en outre, le concept de sénescence à l’échelle de la plante entière en focalisant sur le rôle de la floraison dans la durée de vie de la plante. Dans un second temps, la revue se focalise sur le processus de sénescence foliaire et le rôle des hormones végétales et du statut nutritif dans la régulation de l’apparition et de l’intensité des symptômes de sénescence. L’implication de l’autophagie et de la kinase Target of Rapamycin (TOR) dans l’adaptation des plantes à leur milieu et dans le contrôle de leur croissance et de leur mort est particulièrement discutée

Antifungal activities of wood extractives

Extractives are non-structural wood molecules that represent a minor fraction in wood.However, they are source of diverse molecules putatively bioactive. Inhibition of fungal growth is one of the most interesting properties of wood extractives in a context of wood preservation, crop protection or medical treatments.The antifungal effect of molecules isolated from wood extractives has been mainly attributed to various mechanisms such as metal and free radical scavenging activity, direct interaction with enzymes, disruption of membrane integrity and perturbation of ionic homeostasis. Lignolytic fungi, which are microorganisms adapted to wood substrates, have developed various strategies to protect themselves against this toxicity.A better knowledge of these strategies could help both developing new systems for extractive removal in biomass valorization processes and using these molecules as antifungal agents. (C) 2017 British Mycological Society

The TOR complex and signaling pathway in plants

The mechanisms of plant growth and development are specific and have been shaped by their evolution as immobile, autotrophic and multicellular organisms. Indeed, plant growth is highly plastic, relatively undetermined, and strongly influenced by external conditions. Signaling pathways must therefore constantly link environmental inputs to growth and development. Among the known eukaryotic pathways, target of rapamycin (TOR) signaling, a central component of the perception and transduction of exogenous signals, has been shown to link cell and organism growth to the environment. But little is so far known on this signaling pathway in photosynthetic organisms. In this review, we summarize recent studies that address the nature of TOR complexes and signaling in plants, highlighting similarities and differences with respect to other eukaryotic kingdoms

Modes‐of‐action of antifungal compounds: Stressors and (target‐site‐specific) toxins, toxicants, or Toxin–stressors

Abstract Fungi and antifungal compounds are relevant to the United Nation's Sustainable Development Goals. However, the modes‐of‐action of antifungals—whether they are naturally occurring substances or anthropogenic fungicides—are often unknown or are misallocated in terms of their mechanistic category. Here, we consider the most effective approaches to identifying whether antifungal substances are cellular stressors, toxins/toxicants (that are target‐site‐specific), or have a hybrid mode‐of‐action as toxin–stressors (that induce cellular stress yet are target‐site‐specific). This newly described ‘toxin–stressor’ category includes some photosensitisers that target the cell membrane and, once activated by light or ultraviolet radiation, cause oxidative damage. We provide a glossary of terms and a diagrammatic representation of diverse types of stressors, toxic substances, and toxin–stressors, a classification that is pertinent to inhibitory substances not only for fungi but for all types of cellular life. A decision‐tree approach can also be used to help differentiate toxic substances from cellular stressors (Curr Opin Biotechnol 2015 33: 228–259). For compounds that target specific sites in the cell, we evaluate the relative merits of using metabolite analyses, chemical genetics, chemoproteomics, transcriptomics, and the target‐based drug‐discovery approach (based on that used in pharmaceutical research), focusing on both ascomycete models and the less‐studied basidiomycete fungi. Chemical genetic methods to elucidate modes‐of‐action currently have limited application for fungi where molecular tools are not yet available; we discuss ways to circumvent this bottleneck. We also discuss ecologically commonplace scenarios in which multiple substances act to limit the functionality of the fungal cell and a number of as‐yet‐unresolved questions about the modes‐of‐action of antifungal compounds pertaining to the Sustainable Development Goals

Saccharomyces cerevisiae FKBP12 binds Arabidopsis thaliana TOR and its expression in plants leads to rapamycin susceptibility

International audienceBackground The eukaryotic TOR pathway controls translation, growth and the cell cycle in response to environmental signals such as nutrients or growth-stimulating factors. The TOR protein kinase can be inactivated by the antibiotic rapamycin following the formation of a ternary complex between TOR, rapamycin and FKBP12 proteins. The TOR protein is also found in higher plants despite the fact that they are rapamycin insensitive. Previous findings using the yeast two hybrid system suggest that the FKBP12 plant homolog is unable to form a complex with rapamycin and TOR, while the FRB domain of plant TOR is still able to bind to heterologous FKBP12 in the presence of rapamycin. The resistance to rapamycin is therefore limiting the molecular dissection of the TOR pathway in higher plants. Results Here we show that none of the FKBPs from the model plant Arabidopsis (AtFKBPs) is able to form a ternary complex with the FRB domain of AtTOR in the presence of rapamycin in a two hybrid system. An antibody has been raised against the AtTOR protein and binding of recombinant yeast ScFKBP12 to native Arabidopsis TOR in the presence of rapamycin was demonstrated in pull-down experiments. Transgenic lines expressing ScFKBP12 were produced and were found to display a rapamycin-dependent reduction of the primary root growth and a lowered accumulation of high molecular weight polysomes. Conclusion These results further strengthen the idea that plant resistance to rapamycin evolved as a consequence of mutations in plant FKBP proteins. The production of rapamycin-sensitive plants through the expression of the ScFKBP12 protein illustrates the conservation of the TOR pathway in eukaryotes. Since AtTOR null mutants were found to be embryo lethal [1], transgenic ScFKBP12 plants will provide an useful tool for the post-embryonic study of plant TOR functions. This work also establish for the first time a link between TOR activity and translation in plant cell

Higher plant chloroplasts import the mRNA coding for the eucaryotic translation initiation factor 4E.

International audiencePlant chloroplasts probably originate from an endosymbiosis event between a photosynthetic bacteria and a eucaryotic cell. The proper functioning of this association requires a high level of integration between the chloroplastic genome and the plant cell genome. Many chloroplastic genes have been transferred to the nucleus of the host cell and the proteins coded by these genes are imported into the chloroplast. Chloroplastic activity also regulates the expression of these genes at the transcriptional and post-transcriptional levels. The importation of nucleic acids from the host cell into the chloroplast has never been observed. This work show that the mRNA coding for the eucaryotic translation factor 4E, an essential regulator of translation, enters the chloroplast in four different plant species, and is located in the stroma. Furthermore, the localization in the chloroplast of an heterologous GFP mRNA fused to the eIF4E RNA was also observed

Mediation with Dichotomous Outcomes

This is a draft document to assist researchers. Please do not cite or quote without the author’s permission. I thank both Nathaniel R. Herr and Craig Nathanson who suggested corrections to a prior document. Readers might benefit by consulting the page by Nathaniel Herr