Hitchhiking of bactericidal/permeability-increasing protein-like gene with the fibromelanosis locus in Kadaknath black-bone-chicken

Abstract

Black-bone-chicken (BBC) breeds are famous for their distinctive meat texture and taste. However, the relationship between BBC breeds, especially the Kadaknath breed native to India, is poorly understood. Here, we establish that all BBC breeds, including Kadaknath, share a common complex chromosomal rearrangement at the FM locus on the 20th chromosome, which is responsible for the melanin hyperpigmentation throughout the body. While we find breed-specific gene flow between BBC and commercial breeds, the shared ancestry of all BBC breeds and pattern of isolation by distance suggest Kadaknath is closely related to Tibetan BBC. Interestingly, two FM locus proximal regions (~70Kb and ~300 Kb) have signatures of selection unique to Kadaknath. These regions harbor several genes with protein-coding changes, with the Bactericidal/permeability-increasing-protein-like (BPIL) gene having two Kadaknath-specific changes within the protein domains. The absence of these changes in other BBC breeds suggests this variation arose after the separation of these breeds. Our results indicate that the rearrangement at the FM locus and protein-coding changes in the BPIL gene were selected simultaneously in Kadaknath due to close physical linkage. The identification of this FM locus proximal selective sweep sheds light on the distinctiveness of Kadaknath compared to other BBC.