The snapdragon genomes reveal the evolutionary dynamics of the S locus supergene.

The genus Antirrhinum has been used as a model to study self-incompatibility extensively. The multi-allelic S-locus, carrying a pistil S-RNase and dozens of S-locus F-box (SLF) genes, underlies the genetic control of self-incompatibility (SI) in Antirrhinum hispanicum. However, there have been limited studies on the genomic organization of the S-locus supergene due to a lack of high-quality genomic data. Here, we present the chromosome-level reference and haplotype-resolved genome assemblies of a self-incompatible A.hispanicum line, AhS7S8. For the first time, two complete A.hispanicum S-haplotypes spanning ∼1.2Mb and containing a total of 32 SLFs were reconstructed, while most of the SLFs derived from retroelement-mediated proximal or tandem duplication approximately 122 Mya. Back then, the S-RNase gene and incipient SLFs came into linkage to form the pro-type of type-1 S-locus in the common ancestor of eudicots. Furthermore, we detected a pleiotropic cis-transcription factor associated with regulating the expression of SLFs, and two miRNAs may control the expression of this transcription factor. Inter-specific S-locus and intra-specific S-haplotype comparisons revealed the dynamic nature and polymorphism of the S-locus supergene mediated by continuous gene duplication, segmental translocation or loss, and TE-mediated transposition events. Our data provide an excellent resource for future research on the evolutionary studies of the S-RNase-based self-incompatibility system.