Over-expression of a chimeric gene of the transcriptional co-activator MBF1 fused to the EAR repressor motif causes developmental alteration in Arabidopsis and tomato

Transcriptional co-activators of the Multiprotein Bridging Factor1 (MBF1) type belong to a multigenic family that encode key components of the machinery controlling gene expression by communicating between transcription factors and the basal transcription machinery. Knocking-down the expression of one member of the family has proved difficult probably due to functional redundancy. We show here that a fusion of SlER24, an MBF1 type gene of tomato, to the Ethylene-responsive element-binding associated Amphiphilic Repression (EAR) motif is capable of slowing down significantly the expression of the GFP protein driven by a synthetic ethylene-responsive GCC-rich promoter in a single cell transient expression system. A fusion of AtMBF1c of Arabidopsis to EAR, driven by the 35S promoter, caused a reduction of the percentage of seed germination and dwarfism of the plant. Similar fusion with the SlER24 of tomato in the MicroTom cultivar induced a delay of seed germination and no obvious effect on plant growth. Besides giving information on the role of the MBF1 genes in plant development, this study demonstrates that the EAR strategy is efficient not only for regular transcription factors as demonstrated so far, but also in the case of co-activators known to not bind directly to DNA

Understanding the effect of cell disruption methods on the diffusion of Chlorella vulgaris proteins and pigments in the aqueous phase

Cell disruption of microalgae is usually evaluated by microscopic observations and quantification of the target molecules before and after cell disruption. The following study considers a new approach by analysing the diffusion behaviour of proteins and pigments of Chlorella vulgaris in an aqueous medium after applying different cell disruption methods. Results were revealed by microscopic observations, quantifying the concentration of the molecules of interest, and calculating their diffusion coefficient. Microscopic observations showed intact cells after applying chemical hydrolysis and ultrasonication. However, the majority of the cells lost their globular shape after bead milling and high-pressure homogenization. The protein concentration increased in the following order: ultrasonication bead milling > ultrasonication > high-pressure homogenization. Pigments were not detected in the aqueous phase of the chemical hydrolysis treatment, but their concentration and their diffusion were in the same order as proteins in the mechanical treatments. The study implied that diffusivity of the target molecules was not directly correlated to their increase concentration in the aqueous phase. Therefore, even if the cells were completely broken, diffusivity followed the hindered molecule diffusion phenomenon, which implies that somehow cells are not completely disrupted

Autoacetylation of the Ralstonia solanacearum Effector PopP2 Targets a Lysine Residue Essential for RRS1-R-Mediated Immunity in Arabidopsis

Type III effector proteins from bacterial pathogens manipulate components of host immunity to suppress defence responses and promote pathogen development. In plants, host proteins targeted by some effectors called avirulence proteins are surveyed by plant disease resistance proteins referred to as “guards”. The Ralstonia solanacearum effector protein PopP2 triggers immunity in Arabidopsis following its perception by the RRS1-R resistance protein. Here, we show that PopP2 interacts with RRS1-R in the nucleus of living plant cells. PopP2 belongs to the YopJ-like family of cysteine proteases, which share a conserved catalytic triad that includes a highly conserved cysteine residue. The catalytic cysteine mutant PopP2-C321A is impaired in its avirulence activity although it is still able to interact with RRS1-R. In addition, PopP2 prevents proteasomal degradation of RRS1-R, independent of the presence of an integral PopP2 catalytic core. A liquid chromatography/tandem mass spectrometry analysis showed that PopP2 displays acetyl-transferase activity leading to its autoacetylation on a particular lysine residue, which is well conserved among all members of the YopJ family. These data suggest that this lysine residue may correspond to a key binding site for acetyl-coenzyme A required for protein activity. Indeed, mutation of this lysine in PopP2 abolishes RRS1-R-mediated immunity. In agreement with the guard hypothesis, our results favour the idea that activation of the plant immune response by RRS1-R depends not only on the physical interaction between the two proteins but also on its perception of PopP2 enzymatic activity

Cinéma et archéologie extraterrestre

International audienc

Cinéma et archéologie extraterrestre.

National audienceCertains scénarios de films de science-fiction, d’épisodes de séries télévisées ou de documentaires sont basés sur et ou développent le thème de la recherche et de la découverte des civilisations extraterrestres et leurs diverses conséquences. Cette étude a pour objectif de démêler le vrai du faux en comparant les faits à la fiction dans les films et les séries télévisées. Certains films sélectionnés ont été classés en deux catégories, selon l’emplacement des découvertes fictives de vestiges de civilisations extraterrestres : sur Terre ou sur d’autres planètes. Les résultats soulignent que si les films de fiction sont souvent inspirés de théories ufologiques controversées telles que celle des « anciens astronautes », certains d’entre eux mettent également l’accent sur des préoccupations scientifiques sérieuses telles que le risque de contamination biologique

Tyrosine Nitration of Flagellins: a Response of Sinorhizobium meliloti to Nitrosative Stress

International audienceRhizobia are bacteria which can either live as free organisms in the soil or interact with plants of the legume family with, as a result, the formation of root organs called nodules in which differentiated endosymbiotic bacteria fix atmospheric nitrogen to the plant's benefit. In both lifestyles, rhizobia are exposed to nitric oxide (NO) which can be perceived as a signaling or toxic molecule. NO can act at the transcriptional level but can also modify proteins by S-nitrosylation of cysteine or nitration of tyrosine residues. However, only a few molecular targets of NO have been described in bacteria and none of them have been characterized in rhizobia. Here, we examined tyrosine nitration of Sinorhizobium meliloti proteins induced by NO. We found three tyrosine-nitrated proteins in S. meliloti grown under free-living conditions, in response to an NO donor. Two nitroproteins were identified by mass spectrometry and correspond to flagellins A and B. We showed that one of the nitratable tyrosines is essential to flagellin function in motility.IMPORTANCE Rhizobia are found as free-living bacteria in the soil or in interaction with plants and are exposed to nitric oxide (NO) in both environments. NO is known to have many effects on animals, plants, and bacteria where only a few molecular targets of NO have been described so far. We identified flagellin A and B by mass spectrometry as tyrosine-nitrated proteins in Sinorhizobium meliloti in vivo. We also showed that one of the nitratable tyrosines is essential to flagellin function in motility. The results enhanced our understanding of NO effects on rhizobia. Identification of bacterial flagellin nitration opens a new possible role of NO in plant-microbe interactions