Assembly of a Multifunctional Speciation Island in Petunia

Petunia axillaris and Petunia exserta are two closely related sister species which are adapted to pollination by nocturnal hawkmoths and hummingbirds, respectively. The flowers of the species differ in visible colour, UV reflectance, scent and reproductive organ morphology. Loci of large effect specifying these floral traits cluster within 1 cM on chromosome II. Since this region harbours at least three distinct genes involved in reproductive isolation, it constitutes a striking example of a speciation island (Hermann et al. Curr Biol 2013).To pin down candidate genes and investigate the structure and characteristics of the introgressed region, long and short-read genome sequencing as well as RNA sequencing of the parents and the introgression lines has been performed. We are additionally using long read sequencing (PacBio) of BACs to assemble the region on chromosome II. So far RNA-seq data has been used to genotype and to detect sequences within introgressed regions. Sequencing data from introgressed regions has been extracted and will be assembled separately to reduce complexity and gain maximal continuity of the assembly. Preliminary results indicate the region to be much larger than was genetically expected, harbouring over 900 genes.