Comparative linkage mapping of diploid, tetraploid, and hexaploid Avena species suggests extensive chromosome rearrangement in ancestral diploids.

The genus Avena (oats) contains diploid, tetraploid and hexaploid species that evolved through hybridization and polyploidization. Four genome types (named A through D) are generally recognized. We used GBS markers to construct linkage maps of A genome diploid (Avena strigosa x A. wiestii, 2n = 14), and AB genome tetraploid (A. barbata 2n = 28) oats. These maps greatly improve coverage from older marker systems. Seven linkage groups in the tetraploid showed much stronger homology and synteny with the A genome diploids than did the other seven, implying an allopolyploid hybrid origin of A. barbata from distinct A and B genome diploid ancestors. Inferred homeologies within A. barbata revealed that the A and B genomes are differentiated by several translocations between chromosomes within each subgenome. However, no translocation exchanges were observed between A and B genomes. Comparison to a consensus map of ACD hexaploid A. sativa (2n = 42) revealed that the A and D genomes of A. sativa show parallel rearrangements when compared to the A genomes of the diploids and tetraploids. While intergenomic translocations are well known in polyploid Avena, our results are most parsimoniously explained if translocations also occurred in the A, B and D genome diploid ancestors of polyploid Avena.