Résumé
Within the Musa Genomics Consortium three BAC libraries were constructed from the genomes of Musa acuminata (cvs 'Calcutta 4' and 'Grande naine') and Musa balbisiana (PKW). The three BAC libraries have been anchored to the existing Musa consensus genetic map using a set of single-copy RFLP markers. The three BAC libraries are a publicly available resource and represent a critical tool to achieve the goals of the recently created Global Musa Genomics Consortium. To study the structure and evolution of Musa genomes in relation to those of rice and sorghum, 50 Sorghum bicolor cDNA clones, previously mapped in sorghum and rice with large-hybridization spectrum (EGRAM genes), were used as probes to screen the M. acuminata 'Calcutta-4' BAC library. Banana BACs that hybridized to 9 EGRAM probes of known function were further analysed by BAC end sequencing and RFLP fingerprinting, and individual BAC clones were selected and subcloned for complete sequencing. In addition, BAC clones believed to arise from the homoeologous region on the A and B Musa genomes were identified using M. acuminata RFLP genetically mapped probes encoding for genes of agronomic interest and involved in plant defense (1-3 glucanase) and control of plant height (GA 20-oxidase). Altogether, 13 Musa BACs have been sequenced, totalling over one Mb. A preliminary analysis showed that the gene density in the sampled Musa genomic regions was approximately one per 5 kb and that coding regions are 65-75% similar to those from both rice and Arabidopsis. The relationship between rice and Arabidopsis genomes and the gene content and organization of the sequenced banana regions the will be reported. The first insights provided by the international Musa sequencing project cover: 1. the relationship between duplicated regions within the M. acuminata genome, 2. the comparison of orthologous genomic regions in rice and banana, 3. the conservation of homoeologous regions in M. acuminata and M. balbisiana. These data will shed some light on the relationships, at the microsynteny level, between chromosomal regions of agronomic interest for banana breeding in distantly related monocot species. (Texte intégral)