Novel Symbiotic Regulatory Genes Identified by Transcriptomics in Medicago truncatula

Forward genetics has been extremely fruitful in the recent past to identify key genes involved in the very early stages of symbiotic signaling in model legumes. However, the number of regulatory genes, particularly transcription-factor genes, demonstrated to play a role in the control of the formation of an infected nodule remains very limited. Transcriptomics represents a complementary approach to forward genetics. It can be very powerful for identifying such genes, now that efficient reverse genetics tools have been set up for model legumes. Further, transcriptomics is likely the best method to give a global view of the range of genes that accompany a developmental program, and to compare it to other kinds of developmental program, e.g., symbiotic vs. pathogenic interactions or root-nodule formation vs. lateral-root formation. Transcriptomics approaches have already been used to get a view of the range of genes associated with the nodulation process. We report here on the last global approach used in the frame of the European Grain Legume Integrated Project. This approach was based on 70-mer oligonucleotide microarrays, provided by Helge Kuester, Bielefeld, representing about 16,000 Medicago truncatula genes.