The molecular genetic linkage map of the model legume Medicago truncatula: an essential tool for comparative legume genomics and the isolation of agronomically important genes

BACKGROUND: The legume Medicago truncatula has emerged as a model plant for the molecular and genetic dissection of various plant processes involved in rhizobial, mycorrhizal and pathogenic plant-microbe interactions. Aiming to develop essential tools for such genetic approaches, we have established the first genetic map of this species. Two parental homozygous lines were selected from the cultivar Jemalong and from the Algerian natural population (DZA315) on the basis of their molecular and phenotypic polymorphism. RESULTS: An F2 segregating population of 124 individuals between these two lines was obtained using an efficient manual crossing technique established for M. truncatula and was used to construct a genetic map. This map spans 1225 cM (average 470 kb/cM) and comprises 289 markers including RAPD, AFLP, known genes and isoenzymes arranged in 8 linkage groups (2n = 16). Markers are uniformly distributed throughout the map and segregation distortion is limited to only 3 linkage groups. By mapping a number of common markers, the eight linkage groups are shown to be homologous to those of diploid alfalfa (M. sativa), implying a good level of macrosynteny between the two genomes. Using this M. truncatula map and the derived F3 populations, we were able to map the Mtsym6 symbiotic gene on linkage group 8 and the SPC gene, responsible for the direction of pod coiling, on linkage group 7. CONCLUSIONS: These results demonstrate that Medicago truncatula is amenable to diploid genetic analysis and they open the way to map-based cloning of symbiotic or other agronomically-important genes using this model plant

Single-electron transistor made of multiwalled carbon nanotube using scanning probe manipulation

We positioned semiconducting multiwalled carbon nanotube, using an atomic force microscope, between two gold electrodes at SiO2 surface. Transport measurements exhibit single-electron effects with a charging energy of 24 K. Using the Coulomb staircase model, the capacitances and resistances between the tube and the electrodes can be characterized in detail.Peer reviewe

Search for non-Gaussian events in the data of the VIRGO E4 engineering run

International audienc

Michel Journet : témoignage

National audienc

Michel Journet : témoignage

National audienc

Rethinking agricultural systems and the role of herbivores

Agricultural systems can benefit from the nitrogen (N) and carbon (C) contributed by natural processes, such as photosynthesis and bacteria mediated fixation. Based on their professional experiences and discussions with innovative farmers, M. Journet and J.-P. Dulphy detail their thoughts on the unique role of ruminants in N and C cycles. Whether in the soil or in the rumen, the N cycle depends on C flows and microbial populations; N metabolism and use is optimised when the C/N ratio is about 20. Certain agricultural practices aim for balanced nutrient restitution and thus promote the autonomy and longevity of production systems. Such practices include raising ruminant livestock, using legume cover crops, integrating legume cover crops into commercial crop systems, increasing the surface area dedicated to grasslands, and choosing ruminant livestock based on their ability to recycle C and N.L'agriculture peut bénéficier des disponibilités naturelles d'azote et de carbone via la fixation symbiotique et la photosynthèse. Dans le sol comme dans le rumen, le cycle de l'azote est dépendant des flux de carbone et des populations microbiennes. La réorganisation et valorisation de N est optimale quand le ratio C/N est d'environ 20 dans le rumen comme dans le sol. Les restitutions des herbivores ont un faible ratio C/N, favorable à la minéralisation de N dans le sol et donc à son utilisation par le couvert végétal. Les pratiques agricoles visant des restitutions de composition équilibrée favorisent l'autonomie et la pérennité des systèmes de production : utiliser les couverts avec légumineuses, les intégrer dans les systèmes de grandes cultures, accroître la place des prairies, adapter le type de ruminant pour favoriser son rôle de recycleur de C et N... Plusieurs témoignages d'agriculteurs sont présentés