​The staple diet for a large part of humanity, common wheat (Triticum aestivum L.) is the most cultivated cereal in the world. Scientists want to decipher its genome to identify genes of agronomic interest, and to streamline varietal improvement. However, this sequencing is not an easy task. Indeed, our current wheat, resulting from two successive hybridizations of wild cereals, has a triple genome. In total, its twenty-one chromosomes (seven per sub-genome) have seventeen billion base pairs1 and over 90,000 genes. The International Wheat Genome Sequencing Consortium (IWGSC) has been working at this since 2005.

A mostly French group led by INRA, and in which the CEA-IG (Genoscope) was responsible for establishing an ad hoc sequencing strategy and its implementation, has just published the reference sequence of chromosome 3B, the largest of all with almost one billion base pairs. This work has revealed 7,700 genes distributed in a particular structure: those for basal metabolism are located more in the central region, whereas genes more specific to a tissue or developmental stage are grouped mainly towards the extremities of the chromosome. The comparison with genomic data from closely related species, such as rice or sorghum, shows that successive genomic rearrangements have occurred “recently” in cultivated wheat.

In the same issue of Science, the IWGSC, of which the CEA-IG (Genoscope) is involved, published a draft of the complete genome distributed over the different chromosomes. Now with this overview, and in light of methods and tools developed for chromosome 3B, the Consortium wants to establish the complete reference genome within three years. Scientists from INRA and the CEA have already taken on the sequencing of the two other chromosomes: 1B and 4B.

1 This is five times the size of the human genome.