How environmental stresses affect M. truncatula root architecture?

O LELANDAIS, C; NAYA, L; ZAHAF, O; ARIEL, F; PLET, J; LAFFONT, C; SALLET, E; CHAN, R; DIET, A; GRUBER, V; GOUZY, J; HARTMANN, C; FRUGIER, F AND CRESPI, M

Puerto Vallarta, México

Conferencia; 4th International Conference on Legume Genomics and Genetics; 2008

Universidad de Cuernavaca

The root system is crucial for crop productivity and the acquisition of soil resources (nutrients and water). Plants can adapt and optimise their root architecture by initiating primordia and influencing growth of primary or lateral roots in order to adapt the root system to the soil environment. In contrast to Arabidopsis, legumes are additionally able to develop specific organogenesis through symbiotic interactions such as the nitrogen-fixing root nodule. We are using genomic tools in the model legume Medicago truncatula to explore how environmental stresses affect root architecture. Using expression analysis of 16000 genes (Mt16kOLI1Plus microarray) as well as other genomic approaches (substractive hybridization, massive quantitative RT-PCR) we have identified a collection of regulatory genes affected by salt stress in root apexes, the region of the root where the meristem lies and that determines further root growth. Statistical analyses revealed significant changes in 826 genes after a one hour stress with 100 mM NaCl. Among them, 106 sequences corresponded to transcription factors (TF), including members of HD-ZIP, NAC/NAM, WRKY, Dof Zn-finger, MYB, EREBP and PR/ERF families. Their role is being analysed using functional approaches in composite plants and/or M. truncatula TILLING mutants. The dynamics of the transcriptome is determined by the coordinated action of transcription factors and microRNAs, emerging regulators of differentiation and adaptation to environmental constraints. In the legume model M. truncatula, we showed that two miRNAs, miR166 and miR169, are involved in nodule and root development. To investigate the diversity of small RNAs acting during nodulation and in salt stress responses in legume roots, large scale sequencing of small RNA populations from mature nodules and root apexes treated or not by NaCl 100mM was performed using 454 technology. This yield 82 519 small RNAs from 18 to 25 nt from which 28 000 displayed a miRNA-precursor like secondary structure at one predicted genomic locus. Alignment with the miRNA database, miRBASE, revealed more than 17 000 sequences corresponding to conserved miRNA families. Comparison of miRNA frequencies between nodules, root apexes and stressed-roots identify conserved miRNAs potentially induced during nodulation (e.g. miR157 and miR167) or enriched in root apexes (e.g. miR170 and miR390) or under stress conditions (e.g. miR398). The remaining sequences could correspond to legume-specific miRNAs regulated during these processes. The combination of genomics, functional and physiological analysis in the model legume will provide new molecular markers for breeding programs and, most importantly, can significantly accelerate the characterization of key genes and networks involved in the control of legume adaptation to abiotic stresses.