Two ancient genome duplication events shape diversity in Hibiscus L. (Malvaceae)

Background: The great diversity in plant genome size and chromosome number is partly due to polyploidization (i.e., genome doubling events). The differences in genome size and chromosome number among diploid plant species can be a window into the intriguing phenomenon of past genome doubling that may be obscured through time by the process of diploidization. The genus Hibiscus L. (Malvaceae) has a wide diversity of chromosome numbers and an allegedly complex genomic history. Hibiscus is ideal for exploring past genomic events because although two ancient genome duplication events have been identified, as more are still likely to be found, considering its diverse background. To reappraise the group’s genomic history, we tested a series of scenarios describing different polyploidization events using previously identified duplications in Hibiscus syriacus.Results: The data showed that >54% of the single-copy genes where in fact paralogues. When testing for different genome duplication scenarios using gene count data; species of Hibiscus was shown to have shared one genome duplication with H. syriacus, -- while one whole genome duplication was contained within H. syriacus, -- to be the preferred model given the observed distribution of paralogous gene copies in Hibiscus.Conclusions: Here, we corroborated the independent genome doubling previously found in the lineage leading to H. syriacus and a shared genome doubling of this lineage and the remainder of Hibiscus. Additionally, we found a previously undiscovered genome duplication shared by the /Pavonia and /Malvaviscus clades (both nested within Hibiscus) with the occurrences of two copies in what were otherwise single-copy genes. Our results highlight the complexity of genomic diversity in some plant groups, which makes orthology assessment and accurate phylogenomic inference difficult.