Fig. 4

Genome evolutionary history of Pennisetum giganteum. a Distribution of inter- or intra-species synonymous substitution rates (Ks) indicates whole-genome duplication (WGD) events and species divergence time. The different colored curves indicate the Ks distribution of syntelogues between two species or subgenomes of the same species. b Genome-wide synteny analysis between P. giganteum and C. americanus. c Genome-wide synteny analysis between P. giganteum and S. viridis. d Chromosome number evolution of grass species detected by genome-wide comparison across two subgenomes of P. giganteum and two other species. The syntenic blocks among S. bicolor, S. viridis, and the A and B subgenomes of P. giganteum were generated using the JCVI utility (Python version of MCScan). e Reconstructed ancestral grass karyotype based on five extant grass species, namely P. giganteum, S. bicolor, Z. mays, S. viridis, and C. americanus, using the IAGS pipeline. The inferred karyotypes of five ancestry nodes and the five representative grass species are displayed together with a schematic species tree that shows the evolutionary history of these grass species. The red triangle indicates the polyploidization event and the green pentagram indicates the WGD event. The timeline (leftmost) indicates species divergence times in Mya. Chromosome numbers of the five grass species are given below the karyotypes of each species. Divergence times of (1) S. bicolor and C. americanus, (2) S. bicolor and Z. mays, (3) S. viridis and P. giganteum, and (4) P. giganteum and C. americanus