Unraveling the determinants of freezing tolerance in Medicago truncatula : a first step toward improving the response of crop legumes to freezing stress using translational genomics

Freezing is a major environmental limitation that affects biomass and seed productivity in a large number of crop species including legumes. Medicago truncatula is a model molecular‐genetic system for legume biology. A strategy to decipher freezing tolerance after a cold acclimation period in M. truncatula was developed using a quantitative genetic approach. Three main quantitative trait loci (QTL) with additive effects for freezing damage were detected on chromosomes 1, 4, and 6 using a recombinant inbred line population derived from a cross between the freezing‐tolerant accession F83005‐5 and the freezing‐sensitive accession DZA045‐5. The QTL on chromosome 6, named Mt‐FTQTL6, explained 40% of the phenotypic variance. Fine mapping of Mt‐FTQTL6 led to the identification of 20 positional candidate genes. Twelve of these 20 genes belong to the C‐repeat binding factor/dehydration‐responsive element binding factor 1 group of the AP2/EREBP transcription factor family and are tandemly arrayed. Non‐synonymous single nucleotide polymorphism (SNP) mutations, indels, and copy number variations were identified as putative candidate polymorphisms in CBF/DREB1 genes to explain the difference in freezing tolerance between the parental M. truncatula accessions. These important findings pave the way for translational applications to improve freezing tolerance in crop legumes such as pea, lentil, faba bean, and alfalfa