Background: Finger millet (Eleusine coracana 2n=4x=36 ) is a hardy, nutraceutical, climate change tolerant, orphan crop that is consumed throughout eastern Africa and India. Its genome has been sequenced multiple times, but A and B subgenomes could not be separated because no published genome for E. indica existed. The classification of A and B subgenomes is important for understanding the evolution of this crop and provide a means to improve current and future breeding programs.
Results:We produced subgenome calls for 704 syntenic blocks and inferred A or B subgenomic identity for 59,377 genes 81% of the annotated genes. Phylogenetic analysis of a super matrix containing 455 genes shows high support for A and B divergence within the Eleusine genus.
Synonymous substitution rates between A and B genes supports A and B calls. The repetitive contenton highly supported B contigs is higher than that on similar A contigs. Analysis of syntenic singletons showed evidence of biased fractionation showed a pattern of A genome dominance, with 61% A , 37% B and 1% unassigned, and was further supported by the pattern of loss observed among cyto-nuclear interacting genes. Examination of expression within the ciradian rhythm pathway suggests A subgenomic preference.
Conclusion:The evidence of individual gene calls within each syntenic block, provides a powerful tool for inference for subgenome classification. Our results show the utility of a draft genome in resolving A and B subgenomes calls, primarily it allows for the proper polarization of A and B syntenic blocks. There have been multiple calls for the use of phylogenetic inference in subgenome classification, our use of synteny is a practical application in a system that has only one parental genome available.
BackgroundEleusine coracana (finger millet) is an important small-seed cereal crop in its native Africa and South Asia [1,2]. It is believed to be the product of an allopolyploid hybridization between E. indica and another likely extinct species [3][4][5][6][7]. Eleusine indica is consistently identified as an A genome donor [3, 4], however, based on the strength plastid phylogenetic analysis, some have suggested that E. coracana is the result of multiple hybridization events, between the B genome donor, E. indica and E.