The heat shock response in moss plants is regulated by specific calcium-permeable channels in the plasma membrane.

Land plants are prone to strong thermal variations and must therefore sense early moderate temperature increments to induce appropriate cellular defenses, such as molecular chaperones, in anticipation of upcoming noxious temperatures. To investigate how plants perceive mild changes in ambient temperature, we monitored in recombinant lines of the moss Physcomitrella patens the activation of a heat-inducible promoter, the integrity of a thermolabile enzyme, and the fluctuations of cytoplasmic calcium. Mild temperature increments, or isothermal treatments with membrane fluidizers or Hsp90 inhibitors, induced a heat shock response (HSR) that critically depended on a preceding Ca(2+) transient through the plasma membrane. Electrophysiological experiments revealed the presence of a Ca(2+)-permeable channel in the plasma membrane that is transiently activated by mild temperature increments or chemical perturbations of membrane fluidity. The amplitude of the Ca(2+) influx during the first minutes of a temperature stress modulated the intensity of the HSR, and Ca(2+) channel blockers prevented HSR and the onset of thermotolerance. Our data suggest that early sensing of mild temperature increments occurs at the plasma membrane of plant cells independently from cytosolic protein unfolding. The heat signal is translated into an effective HSR by way of a specific membrane-regulated Ca(2+) influx, leading to thermotolerance.

Cloning of a cDNA encoding a plasma membrane-associated, uronide binding phosphoprotein with physical properties similar to viral movement proteins.

Oligogalacturonides are structural and regulatory homopolymers from the extracellular pectic matrix of plants. In vitro micromolar concentrations of oligogalacturonates and polygalacturonates were shown previously to stimulate the phosphorylation of a small plasma membrane-associated protein in potato. Immunologically cross-reactive proteins were detected in plasma membrane-enriched fractions from all angiosperm subclasses in the Cronquist system. Polygalacturonate-enhanced phosphorylation of the protein was observed in four of the six dicotyledon subclasses but not in any of the five monocotyledon subclasses. A cDNA for the protein was cloned from potato. The deduced protein is extremely hydrophilic and has a proline-rich N terminus. The C-terminal half of the protein was predicted to be a coiled coil, suggesting that the protein interacts with other macromolecules. The recombinant protein was found to bind both simple and complex galacturonides. The behavior of the protein suggests several parallels with viral proteins involved in intercellular communication.

Arbuscular mycorrhiza-specific signaling in rice transcends the common symbiosis signaling pathway.

Knowledge about signaling in arbuscular mycorrhizal (AM) symbioses is currently restricted to the common symbiosis (SYM) signaling pathway discovered in legumes. This pathway includes calcium as a second messenger and regulates both AM and rhizobial symbioses. Both monocotyledons and dicotyledons form symbiotic associations with AM fungi, and although they differ markedly in the organization of their root systems, the morphology of colonization is similar. To identify and dissect AM-specific signaling in rice (Oryza sativa), we developed molecular phenotyping tools based on gene expression patterns that monitor various steps of AM colonization. These tools were used to distinguish common SYM-dependent and -independent signaling by examining rice mutants of selected putative legume signaling orthologs predicted to be perturbed both upstream (CASTOR and POLLUX) and downstream (CCAMK and CYCLOPS) of the central, calcium-spiking signal. All four mutants displayed impaired AM interactions and altered AM-specific gene expression patterns, therefore demonstrating functional conservation of SYM signaling between distant plant species. In addition, differential gene expression patterns in the mutants provided evidence for AM-specific but SYM-independent signaling in rice and furthermore for unexpected deviations from the SYM pathway downstream of calcium spiking.

Quand Jésus fait le procès des juifs: Matthieu 23 et l'antijudaïsme

(Résumé de l'ouvrage) Les 23 et 24 novembre 1996, s'est déroulé à la Faculté de théologie de Toulouse, à l'occasion de la remise d'un volume d'hommages à Simon Légasse, un colloque intitulé « Procès de Jésus, procès des Juifs ? » Le titre du colloque mérite une explication. Le point d'interrogation exprime tout à la fois le questionnement et l'incrédulité devant la possibilité de s'appuyer sur les récits rapportant le procès de Jésus pour mettre en accusation les Juifs. L'association des deux expressions rappelle que l'histoire des chrétiens n'a que trop souvent démontré que le procès de Jésus pouvait servir à justifier des pratiques antijudaïques et antisémites. Au terme du colloque, deux enseignements se dégagent avec force : d'abord que l'ignorance est toujours coupable. Les chrétiens doivent connaître leur dette envers le peuple juif et cesser de caricaturer leur interprétation de la Bible ou de faire comme si le judaïsme s'était éteint à l'avènement du christianisme. Ensuite, que la médiation de la critique historique est essentielle, car les Écritures, Parole de Dieu, sont aussi parole humaine et l'on s'expose à de dangereuses dérives si l'on oublie de tenir compte de leur historicité.