In species with separate sexes, sex chromosomes are believed to play a major role in reproductive isolation. We will test this hypothesis on a group of four plant species belonging to the Otites section of the genus Silene where two XY and ZW systems occur. Through interspecies crosses, QTL mapping and transcriptomics, we will assess the occurence of Haldane's rule (stronger impact on the heterogametic sex), the relative involvement of X/Z chromosomes in reproductive isolation. A population genomics approach will complete the analysis in order to establish the best scenarii of speciation of the four species.