Ge2Sb2Te5 layer used as solid electrolyte in conductive-bridge memory devices fabricated on flexible substrate

7 pagesInternational audienceThis paper shows that the well-know chalcogenide Ge2Sb2Te5 (GST) in its amorphous state may be advantageously used as solid electrolyte material to fabricate Conductive-Bridge Random Access Memory (CBRAM) devices. GST layer was sputtered on preliminary inkjet-printed silver lines acting as active electrode on either silicon or plastic substrates. Whatever the substrate, the resistance switching is unambiguously attested at a nanoscale by means of conductive-atomic force microscopy (C-AFM) using a Pt-Ir coated tip on the GST surface acting as a passive electrode. The resistance change is correlated to the appearance or disappearance of concomitant hillocks and current spots at the surface of the GST layer. This feature is attributed to the formation/dissolution of a silver-rich protrusion beneath the AFM tip during set/reset operation. Beside, this paper constitutes a step toward the elaboration of crossbar memory arrays on flexible substrates since CBRAM operations were demonstrated on W/GST/Ag crossbar memory cells obtained from an heterogeneous fabrication process combining physical deposition and inkjet-printing

Etude de la transmission du champignon Alternaria brassicicola à la semence d’Arabidopsis thaliana

National audienc

Roles of hydrophilin-like protein in the filamentous fungi Alternaria brassicicola

During their life cycle, fungi face adverse environmental conditions associated with alterations in water status. Phytopathogenic fungi are faced with this type of stress during the infection process, especially when they colonize seeds. Although these organisms are particularly effective to adapt to these water potential decreases, these coping mechanisms are so far very poorly described, particularly in filamentous fungi. Alternaria brassicicola is a seed-borne fungal pathogen responsible for the black spot disease on Brassicaceae plants. Alteration of Brassicaceae seed quality is one of the most damaging effects of the black spot. Beyond contribution to pathogen dissemination, the presence of the fungus on the seeds compromises seedling germination and survival. To better understand the determinism of fungus transmission to seeds, we previously established a reliable Arabidopsis-based pathosystem allowing investigations of A. brassicicola transmission to seeds. In particular, we showed that two mutants strain ∆abhog and ∆abnik exhibiting higher susceptibility to osmotic and water stress were highly impaired in seed transmission ability. Transcriptomic analyzes, carried out under different experimental in vitro conditions inducing these types of stress (addition of sorbitol or Poly Ethylene Glycol (PEG) or by incubation under low relative humidity (1% RH)), allowed us to identify additional mechanisms potentially involved in the fungal adaptive responses. In particular, these analyzes revealed a pool of over-expressed genes encoding putative proteins which share physiochemical features typical of hydrophilin-like proteins. We initiated studies of some of these hydrophilins by generating respective Knock-Out mutants. Functional studies has been carried out to determine whether these mutants were impaired in their adaptive response to water stress and other types of stress (such as oxidative stress) and whether hydrophilins are involved in pathogenicity. Additional transcriptomic assays conducted on ∆abhog and ∆abnik strain growth under sorbitol exposure revealed that numerous hydrophilins are regulated by these two genes

Glucosinolate-derived isothiocyanates impact mitochondrial function in fungal cells and elicit an oxidative stress response necessary for growth recovery

Glucosinolates are brassicaceous secondary metabolites that have long been considered as chemical shields against pathogen invasion. Isothiocyanates, are glucosinolate-breakdown products that have negative effects on the growth of various fungal species. We explored the mechanism by which isothiocyanates could cause fungal cell death using Alternaria brassicicola, a specialist Brassica pathogens, as model organism. Exposure of the fungus to isothiocyanates led to a decreased oxygen consumption rate, intracellular accumulation of reactive oxygen species and mitochondrial-membrane depolarization. We also found that two major regulators of the response to oxidative stress, i.e. the MAP kinase AbHog1 and the transcription factor AbAP1, were activated in the presence of isothiocyanates. Once activated by isothiocyanate-derived reactive oxygen species, AbAP1 was found to promote the expression of different oxidative-response genes. This response might play a significant role in the protection of the fungus against isothiocyanates as mutants deficient in AbHog1 or AbAP1 were found to be hypersensitive to these metabolites. Moreover, the loss of these genes was accompanied by a significant decrease in aggressiveness on Brassica. We suggest that the robust protection response against isothiocyanate-derived oxidative stress might be a key adaptation mechanism for successful infection of host plants by Brassicaceae-specialist necrotrophs like A. brassicicola

La phytoalexine '6-méthoxymélleine' est-t-elle impliquée dans les mécanismes de résistance de la carotte à Alternaria dauci, agent de la brûlure foliaire ?

Cell wall integrity is crucial for fungal growth, development and stress survival. In yeast, Slt2 MAP kinase and calcineurin signaling pathways monitor cell wall repair during stress and development. MPS1, the M. grisea SLT2 orthologue, is essential for cell wall repair and for appressorium mediated penetration into host plants (Xu 1998 PNAS 95:12713). In yeast, Slt2 activates the transcription factors Rlm1, Swi4 and Swi6, while calcineurin activates Crz1. Genes orthologous to yeast CRZ1, MPS1,Cell wall integrity is crucial for fungal growth, development and stress survival. In yeast, Slt2 MAP kinase and calcineurin signaling pathways monitor cell wall repair during stress and development. MPS1, the M. grisea SLT2 orthologue, is essential for cell wall repair and for appressorium mediated penetration into host plants (Xu 1998 PNAS 95:12713). In yeast, Slt2 activates the transcription factors Rlm1, Swi4 and Swi6, while calcineurin activates Crz1. Genes orthologous to yeast CRZ1, MPS1, RLM1, SWI4, and SWI6 genes were identified in M. grisea genome. Swi4 and Swi6 interact with Mps1 in yeast two hybrid assays. Deletion mutants were constructed by targeted gene replacement in M. grisea. Delta-mps1 mutants displayed an abnormal mycelial growth (no aerial hyphae), did not sporulate, and were nonpathogenic on plants as reported. Delta-crz1, delta-rlm1, delta-swi6 mutants have a normal mycelial growth and sporulation rates similar to wild type. Of these three mutants, only delta-Rlm1 displays a highly reduced pathogenicity on barley and rice (-98%, lesion number). Delta-mps1 mutants are highly sensitive to nikkomycin Z (chitin synthase inhibitor), CFW (disorganization of cell wall) and aculeacine (glucan synthase inhibitor), while delta-crz1 and delta-rlm1 mutant are only mildly hypersensitive to Nikkomycin, and delta-swi6 mutant is only slightly hypersensitive to CFW. These studies suggest that the transcription factors controlled by Mps1 are either functionally redundant or specialized in the control of specific target genes