Fresh insights into the Musa genome and its comparison with rice

The aim of this study was to better understand the evolution of the Musa (banana) genome through sequence and phylogenetic analyses. For this purpose, we used a set of large-hybridization spectrum across monocots cDNA probes from Sorghum bicolor to isolate and sequence 11 Musa acuminata BAC clones containing genes with a high degree of sequence conservation among monocots. Comparison of the 11 Musa BAC sequences with the complete genome sequence of rice led to the identification of several syntenic regions between these two species that are likely to reflect highly conserved genomic blocks across monocots. In contrast, comparison between Musa and the more distantly related dicot Arabidopsis thaliana revealed only one case of microcolinearity. To extend our investigations on Musa genome evolution, BAC clones corresponding to two orthologous regions from two cultivated Musa species (Musa A and B) were also isolated and sequenced. Sequence analysis revealed a perfect conservation of gene order and a high level of sequence identity between the two Musa genomic regions. We used a molecular clock approach to estimate the age of divergence between the Musa A and B genomes to circa. 1 Mya. Finally, we analysed the distribution of the ages of pairs of duplicated Musa genes and provide strong evidence that one or more largescale duplication events occurred in the lineage leading to modern Musa species some 42 Mya.