Symbiotic nitrogen fixation: common features between actinorhizal and legume root modules.

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Publication . Svistoonoff, Sergio; Laplaze, Laurent; Liang, Jingsi; Ribeiro, Ana; Gouveia, Manuela C.; Auguy, Florence; Fevereiro, Pedro; Franche, Claudine; Bogusz, Didier

Two nitrogen-fixing root nodule symbioses between soil bacteria and higher plants have been described: the symbiosis between legume and rhizobia and actinorhizal symbioses between plants belonging to eight angiosperm families and the actinomycete Frankia. We have recently shown that the subtilisin-like Ser protease gene cg12 (isolated from the actinorhizal plant Casuarina glauca) is specifically expressed during plant cell infection by Frankia. Here we report on the study of C. glauca cg12 promoter activity in the transgenic legume Medicago truncatula. We found that cg12 promoter activation is associated with plant cell infection by Sinorhizobium meliloti. Furthermore, applications of purified Nod factors and mycorrhizal inoculation failed to trigger expression of the cg12-reporter gene construct. This indicates that at least part of the transcriptional environment in plant cells infected by endosymbiotic nitrogen-fixing bacteria is conserved between legume and actinorhizal plants. These results are discussed in view of recent data concerning molecular phylogeny that suggest a common evolutionary origin of all plants entering nitrogen-fixing root nodule symbioses.

2004Journal article

Open access

Characterization of four defense-related genes up-regulated in root nodules of Casuarina glauca

Publication . Santos, Patrícia; Fortunato, Ana; Graça, Inês; Martins, Sandra Marina; Gouveia, Maria Manuela; Auguy, Florence; Bogusz, Didier; Ricardo, Cândido Pereira Pinto; Pawlowski, Katharina; Ribeiro, Ana

Actinorhizal plants are capable of high rates of nitrogen fixation, due to their capacity to establish a root nodule symbiosis with N2-fixing actinomycetes of the genus Frankia. Nodulation is an ontogenic process which requires a sequence of highly coordinated events. One of these mechanisms is the induction of defense-related events, whose precise role during nodulation is largely unknown. In order to contribute to the clarification of the involvement of defense-related genes during actinorhizal root-nodule symbiosis, we have analysed the differential expression of several genes with putative defense-related functions in Casuarina glauca nodules versus non inoculated roots. Four genes encoding a chitinase (CgChi1), a glutathione S-transferase (CgGst), a hairpin-inducible protein (CgHin1) and a peroxidase (CgPox4) were found to be up-regulated in mature nodules compared to roots. In order to find out to which extend were the encoded proteins involved in nodule protection, development or both, gene regulation studies in response to SA and wounding as well as phylogenetic analysis of the protein sequences were performed. These were further characterized through expression studies after SA-treatment and wounding, and by phylogenetic analysis. We suggest that CgChi1 and CgGst are involved in defense or microsymbiont control and CgPox4 is involved in nodule development. For CgHin1 the question “defense, development or both” remains open.

2009Journal article

Open access

Isolation and characterization of cgchi3, a nodule-specific gene from Casuarina glauca encoding a class III chitinase

Publication . Fortunato, Ana; Santos, Patricia; Graça, Inês; Gouveia, Maria Manuela; Martins, Sandra Marina; Ricardo, Cândido Pereira Pinto; Pawlowski, Katharina; Ribeiro, Ana

Chitinases (EC 3.2.1.14) catalyse the hydrolysis of chitin, a homopolymer of b-1,4-linked N-acetyl-D-glucosamine residues. Plant chitinases are involved in a wide variety of processes; in particular, their expression has been found to be enhanced in symbiotic and pathogenic plant–microbe interactions. During this work we have cloned and characterized a gene encoding a class III chitinase from actinorhizal nodules of Casuarina glauca (cgchi3). CGCHI3 was found to be encoded by a single gene that was specifically activated in nodules as compared with uninoculated control roots and leaves. The expression of this gene was further enhanced in nodules after salicylic acid treatment and completely repressed after wounding. In situ hybridisation analysis revealed that cgchi3 is an early nodulin gene, being expressed in the meristem and in the uninfected cortical cells of young nodules. Based on the obtained results we suggest that this gene is involved in nodule development. This is the first report on a class III chitinase coding gene that is specifically activated during actinorhizal symbiosis.

2007Journal article

Open access