Insights into the Musa genome: syntenic relationships to rice and between Musa species.

BACKGROUND: Musa species (Zingiberaceae, Zingiberales) including bananas and plantains are collectively the fourth most important crop in developing countries. Knowledge concerning Musa genome structure and the origin of distinct cultivars has greatly increased over the last few years. Until now, however, no large-scale analyses of Musa genomic sequence have been conducted. This study compares genomic sequence in two Musa species with orthologous regions in the rice genome. RESULTS: We produced 1.4 Mb of Musa sequence from 13 BAC clones, annotated and analyzed them along with 4 previously sequenced BACs. The 443 predicted genes revealed that Zingiberales genes share GC content and distribution characteristics with eudicot and Poaceae genomes. Comparison with rice revealed microsynteny regions that have persisted since the divergence of the Commelinid orders Poales and Zingiberales at least 117 Mya. The previously hypothesized large-scale duplication event in the common ancestor of major cereal lineages within the Poaceae was verified. The divergence time distributions for Musa-Zingiber (Zingiberaceae, Zingiberales) orthologs and paralogs provide strong evidence for a large-scale duplication event in the Musa lineage after its divergence from the Zingiberaceae approximately 61 Mya. Comparisons of genomic regions from M. acuminata and M. balbisiana revealed highly conserved genome structure, and indicated that these genomes diverged circa 4.6 Mya. CONCLUSION: These results point to the utility of comparative analyses between distantly-related monocot species such as rice and Musa for improving our understanding of monocot genome evolution. Sequencing the genome of M. acuminata would provide a strong foundation for comparative genomics in the monocots. In addition a genome sequence would aid genomic and genetic analyses of cultivated Musa polyploid genotypes in research aimed at localizing and cloning genes controlling important agronomic traits for breeding purposes.

Sequencing Bacillus anthracis typing phages gamma and cherry reveals a common ancestry.

The genetic relatedness of the Bacillus anthracis typing phages Gamma and Cherry was determined by nucleotide sequencing and comparative analysis. The genomes of these two phages were identical except at three variable loci, which showed heterogeneity within individual lysates and among Cherry, Wbeta, Fah, and four Gamma bacteriophage sequences.

Comparative genomics of Brassica oleracea and Arabidopsis thaliana reveal gene loss, fragmentation, and dispersal after polyploidy.

We sequenced 2.2 Mb representing triplicated genome segments of Brassica oleracea, which are each paralogous with one another and homologous with a segmentally duplicated region of the Arabidopsis thaliana genome. Sequence annotation identified 177 conserved collinear genes in the B. oleracea genome segments. Analysis of synonymous base substitution rates indicated that the triplicated Brassica genome segments diverged from a common ancestor soon after divergence of the Arabidopsis and Brassica lineages. This conclusion was corroborated by phylogenetic analysis of protein families. Using A. thaliana as an outgroup, 35% of the genes inferred to be present when genome triplication occurred in the Brassica lineage have been lost, most likely via a deletion mechanism, in an interspersed pattern. Genes encoding proteins involved in signal transduction or transcription were not found to be significantly more extensively retained than those encoding proteins classified with other functions, but putative proteins predicted in the A. thaliana genome were underrepresented in B. oleracea. We identified one example of gene loss from the Arabidopsis lineage. We found evidence for the frequent insertion of gene fragments of nuclear genomic origin and identified four apparently intact genes in noncollinear positions in the B. oleracea and A. thaliana genomes.