Agroinfection-based high-throughput screening reveals specific recognition of INF elicitins in Solanum

We adapted and optimized the use of the Agrobacterium tumefaciens binary PVX expression system (PVX agroinfection) to screen Solanum plants for response to pathogen elicitors and applied the assay to identify a total of 11 clones of Solanum huancabambense and Solanum microdontum , out of 31 species tested, that respond to the elicitins INF1, INF2A and INF2B of Phytophthora infestans . Prior to this study, response to INF elicitins was only known in Nicotiana spp. within the Solanaceae. The identified S. huancabambense and S. microdontum clones also exhibited hypersensitivity-like cell death following infiltration with purified recombinant INF1, INF2A and INF2B, thereby validating the screening protocol. Comparison of INF elicitin activity revealed that Nicotiana plants responded to significantly lower concentrations than Solanum , suggesting variable levels of sensitivity to INF elicitins. We exploited natural variation in response to INF elicitins in the identified Solanum accessions to evaluate the relationship between INF recognition and late blight resistance. Interestingly, several INF-responsive Solanum plants were susceptible to P. infestans . Also, an S. microdontum  × Solanum tuberosum (potato) population that segregates for INF response was generated but failed to identify a measurable contribution of INF response to resistance. These results suggest that in Solanum , INF elicitins are recognized as general elicitors and do not have a measurable contribution to disease resistance.     

Cytopathic Action of Naegleria fowleri Amoebae on Rat Neuroblastoma Target Cells

The axenically cultured, weakly pathogenic Naegleria fowleri LEE and the highly pathogenic, mouse passaged N. fowleri LEEmp are cytopathic for B103 rat nerve cells in culture. Cytopathogenicity was measured by release of radiolabeled rubidium or radiolabeled chromium from B103 target cells. Cytopathogenicity was time-dependent for up to 18 h and dependent upon amoebae effector to nerve cell target ratios of less than 1:1. Release of⁵¹ Cr from B103 cells by either LEE or LEEmp amoebae was enhanced by addition of calcium or magnesium to medium free of these divalent cations but the ion-channel inhibitor, verapamil, or the ionophore A23187 and phorbol myristate acetate did not alter release of ⁵¹ Cr from B103 cells cocultured with the amoebae. Cycloheximide or actinomycin D impaired release of ⁵¹ Cr from B103 target cells injured by either LEE or LEEmp amoebae. Both strains of amoebae were fractionated by glass bead disruption and high speed centrifugation into membrane and soluble fractions. Each fraction was incubated with either ⁸⁶Rb or ⁵¹ Cr labeled nerve cells. The membrane fraction from LEEmp was more active than the soluble fraction in facilitating rubidium and chromium release. In contrast, the soluble fraction from LEE was more active than the membrane fraction in facilitating rubidium release from radiolabeled target cells. The sequential release of ⁸⁶Rb and ⁵¹ Cr from target cells rather than the simultaneous release of the two isotopes indicates that target cell death is due to the release of ions followed later by the release of large macromolecules. The results indicate that N. fowleri amoebae injure nerve cells by two alternate mechanisms, trogocytosis or contact-dependent lysis.     

Caractéristiques Ultrastructurales du Cortex et des Membranelles du CiliéEspejoia mucicola (Oligohymenophora, Hymenostomata, Tetrahymenina)

RESUME. L' étude détaillée du cortex et des organelles buccaux adoraux d' Espejoia montre que ce Cilié possède une organisation ultrastructurale comparable à celle des Tétrahyméniens. Tout en restant conforme au plan général d'organisation de ces derniers, des variations spécifiques décelées tant au niveau du cortex d'une part, que des membranelles, d'autre part, font ressortir des affinités trés marquées pour le genre Glaucoma et autres Ciliés voisins. En conséquence, en nous appuyant en outre sur les données récentes de la morphogenèse, nous confirmons la position d' E. mucicola parmi les Tetrahymenina, dans la famille des Glaucomidae.     

Chemotaxis by Naegleria fowleri for Bacteria1

Naegleria fowleri amebae demonstrated a chemotactic and chemokinetic response toward live cells and extracts of Escherichia coli and other bacterial species when experiments were performed using a blind-well chemotaxis chamber. The peptide N-formyl-methionyl-leucyl-phenylalanine acted as a chemokinetic rather than a chemotactic factor for N. fowleri amebae. Competition experiments in which nerve cell extracts or bacteria were placed on either side of the filter in chemotaxis chambers resulted in increased movement towards bacteria. A scanning electron microscopy study of the interaction of N. fowleri with different bacterial species confirmed that when the amebae were near ingestible bacteria they moved toward the bacteria by pseudopod formation. Naegleria fowleri appeared to respond to bacteria by three interrelated but distinct processes: (a) chemokinesis, (b) chemotaxis, and (c) formation of food cups.     

A novel Arabidopsis–oomycete pathosystem: differential interactions with Phytophthora capsici reveal a role for camalexin,indole glucosinolates and salicylic acid in defence

Phytophthora capsici causes devastating diseases on a broad range of plant species. To better understand the interaction with its host plants, knowledge obtained from a model pathosystem can be instrumental. Here, we describe the interaction between P. capsici and Arabidopsis and the exploitation of this novel pathosystem to assign metabolic pathways involved in defence against P. capsici. Inoculation assays on Arabidopsis accessions with different P. capsici isolates revealed interaction specificity among accession‐isolate combinations. In a compatible interaction, appressorium‐mediated penetration was followed by the formation of invasive hyphae, haustoria and sporangia in leaves and roots. In contrast, in an incompatible interaction, P. capsici infection elicited callose deposition, accumulation of active oxygen species and cell death, resulting in early pathogen encasement in leaves. Moreover, Arabidopsis mutants with defects in salicylic acid signalling, camalexin or indole glucosinolates biosynthesis pathways displayed severely compromised resistance to P. capsici. It is anticipated that this model pathosystem will facilitate the genetic dissection of complex traits responsible for resistance against P. capsici.