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.
Thoquet
Philippe
P
Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, CNRS-INRA, BP27, 31326 Castanet-Tolosan Cedex, France. thoquet@toulouse.inra.fr
Ghérardi
Michele
M
Journet
Etienne-Pascal
EP
Kereszt
Attila
A
Ané
Jean-Michel
JM
Prosperi
Jean-Marie
JM
Huguet
Thierry
T
D002874:Chromosome Mapping / Q000379:methods*; D032461:Chromosomes, Plant / Q000235:genetics*; D018556:Crops, Agricultural / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics / Q000302:isolation & purification; D007887:Fabaceae / Q000235:genetics; D017343:Genes, Plant / Q000235:genetics; D008040:Genetic Linkage; D005819:Genetic Markers / Q000235:genetics; D014644:Genetic Variation; D023281:Genomics / Q000379:methods; D005838:Genotype; D029902:Medicago / Q000235:genetics* / Q000254:growth & development; D010641:Phenotype; D013045:Species Specificity
D018744:DNA, Plant; D005819:Genetic Markers