Arsene et al. (1996) J. Bacteriol. 178,4830-4838


Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, CNRS INTRA, BP27, 31326 Castanet-Tolosan, Cedex France

1. Introduction

The complete sequencing and annotation of the alfalfa symbiont Sinorhizobium meliloti (Galibert et al. 2001) highlighted the presence of genes potentially implicated in the infection process preceding the differentiation of bacteroids and nitrogen fixation. These genes include homologs of virulence genes from plant and mammal intracellular pathogens, cell-surface components, adhesins, outer membrane proteins, pili proteins, regulators, etc. To test the possible implication of these genes in the infection of Medicago truncatula and M. sativa, we have designed nylon gene-arrays with PCR products corresponding to the candidate genes. Arrays were hybridized with cDNAs from S. meliloti grown in various culture conditions and from plant nodules.

2. Results and Discussion

Transcriptome analysis using dedicated nylon gene-arrays enabled to detect the expression of ca. 75% of the genes tested. Control genes behaved as expected thus validating the procedure.

Cluster analysis as well as differential expression made it possible to identify a variety of regulatory patterns. Thanks to the use of both S. meliloti and a plant mutant (Bénaben et al. 1995) blocked at various stages of the symbiotic interaction, we could identify genes that were specifically induced or repressed during the infection of Medicago by S. meliloti. Future work using specific mutants and gene expression fusions is required to characterize their function. Altogether, data suggest that transcriptome experiments are appropriate for the study of the infection process.

Although some improvements of the technique are still needed (e.g. detection of low-expressed genes), the use of whole genome arrays should enable a better understanding of the development of the rhizobium-legume symbiosis

3. References

Bénaben, Duc, Lefebvre, Huguet (1995) Plant Physiol. 107, 53-62 Galibert et al. (2001) Science 293, 668-672

4. Acknowledgements

EK is supported by an INRA post-doctoral fellowship. This work was supported by the Toulouse Génopôle.


C. Bianco1, E. Imperlini1, S. Camerini1, B. Senatore1, R. Calogero2, T. Pandolfmi3,

A. Spena3, R. Defez1

'international Institute of Genetics and Biophysics, Naples-Italy

2Dipartimento di Scienze Cliniche e Biologiche Universita di Torino, Italy

3Dipartimento Scientifico Tecnologico, Facolta di Scienze MM.FF.NN, Verona-Italy

Indole-3-acetic acid (IAA), known to provide auxin activity in higher plants, has been shown to regulate gene expression in prokaryotic systems. IAA is able to circumvent the necessity for cAMP in eliciting gene expression in the arabinose system of E. coli and has an effect on RNA and protein synthesis in this bacterium. However, why indole derivatives can have these abilities is not understood, and this situation illustrates the need for multifaceted approaches in the investigation of cellular metabolism to clarify their mechanisms of action.

We have measured the genomic and proteomic expression patterns of E. coli K-12 following treatment with IAA in a minimal medium using L-arabinose as sole carbon source. In this study, we applied DNA macroarray technology and two-dimensional gel electrophoresis in combination with mass spectrometric identification of selected proteins. We have introduced into Rhizobium leguminosarum bv. viciae two genes converting tryptophan into IAA and observed changes in both of root nodule development and of bacteroid survival and morphology (see Camerini et al. and Senatore et al. this volume). Our results attempt to correlate induction and repression of specific genes/gene products with the expression pattern in both Rhizobium and enteric bacteria.

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