Recent advances in actinorhizal symbiosis signaling

Nitrogen and phosphorus availability are frequent limiting factors in plant growth and development. Certain bacteria and fungi form root endosymbiotic relationships with plants enabling them to exploit atmospheric nitrogen and soil phosphorus. The relationships between bacteria and plants include nitrogen-fixing Gram-negative proteobacteria called rhizobia that are able to interact with most leguminous plants (Fabaceae) but also with the non-legume Parasponia (Cannabaceae), and actinobacteria Frankia, which are able to interact with about 260 species collectively called actinorhizal plants. Fungi involved in the relationship with plants include Glomeromycota that form an arbuscular mycorrhizal (AM) association intracellularly within the roots of more than 80 % of land plants. Increasing numbers of reports suggest that the rhizobial association with legumes has recycled part of the ancestral program used by most plants to interact with AM fungi. This review focuses on the most recent progress made in plant genetic control of root nodulation that occurs in non-legume actinorhizal plant species

Biotechnological strategies for studying actinorhizal symbiosis in Casuarinaceae: transgenesis and beyond

International audienceSince the recovery of the first transgenic plant in the early 1980s, plant transformation technologies have enabled advances in many aspects of basic plant science, including nitrogen-fixing root endosymbioses. Using the biological vectors Agrobacterium tumefaciens and A. rhizogenes, gene constructs have been successfully introduced in the actinorhizal tree species Casuarina glauca, thereby paving the way for functional analysis of the key genes involved in the symbiotic process with the actinobacterium Frankia. In recent years, not only studies of gene promoters in transgenic Casuarinaceae, but also the use of RNA interference to down-regulate genes of interest, have provided new insights into the early stages of the interaction between the root system and the actinobacterium. Opportunities offered by recent developments in genome editing technologies based on the engineered nucleases ZFNs (zinc-finger nucleases), TALENs (transcription activator-like effector nucleases) and RNA-guided CRISPR-Cas (clustered regularly interspaced short palindromic repeats-associated protein/Cas) will be briefly presented

Systems Level Insights Into the Stress Response to UV Radiation in the Halophilic Archaeon Halobacterium NRC-1

We report a remarkably high UV-radiation resistance in the extremely halophilic archaeon Halobacterium NRC-1 withstanding up to 110 J/m(2) with no loss of viability. Gene knockout analysis in two putative photolyase-like genes (phr1 and phr2) implicated only phr2 in photoreactivation. The UV-response was further characterized by analyzing simultaneously, along with gene function and protein interactions inferred through comparative genomics approaches, mRNA changes for all 2400 genes during light and dark repair. In addition to photoreactivation, three other putative repair mechanisms were identified including d(CTAG) methylation-directed mismatch repair, four oxidative damage repair enzymes, and two proteases for eliminating damaged proteins. Moreover, a UV-induced down-regulation of many important metabolic functions was observed during light repair and seems to be a phenomenon shared by all three domains of life. The systems analysis has facilitated the assignment of putative functions to 26 of 33 key proteins in the UV response through sequence-based methods and/or similarities of their predicted three-dimensional structures to known structures in the PDB. Finally, the systems analysis has raised, through the integration of experimentally determined and computationally inferred data, many experimentally testable hypotheses that describe the metabolic and regulatory networks of Halobacterium NRC-1

Les arbres actinorhiziens de la famille des Casuarinaceae : utilisations et étude de la plasticité racinaire face aux contraintes abiotiques

Les plantes susceptibles d’établir une symbiose fixatrice d’azote avec l’actinomycète du sol Frankia sont appelées plantes actinorhiziennes. Ce sont principalement des plantes ligneuses, capables de coloniser des sols pauvres et de tolérer une grande variété de stress. Dans les régions tropicales arides et semi-arides, les arbres actinorhiziens de la famille des Casuarinaceae sont très utilisés pour réhabiliter les sols dégradés, protéger les zones côtières et les cultures de l’ensablement, et fournir du bois de chauffe. Les facultés d’adaptation de Casuarina aux sols carencés en éléments nutritifs sont liées à la plasticité racinaire remarquable de cet arbre qui adapte son programme de développement en fonction de son environnement. Les recherches entreprises dans notre laboratoire visent à comprendre les bases moléculaires de cette plasticité chez l’espèce Casuarina glauca. Des approches génomiques et des études d’analyse fonctionnelle de gènes candidats sont développées en partenariat avec des laboratoires du Sud