Using comparative genomics to detect mutations regulating plumage variations in graylag (A. anser) and swan geese (A....

Although graylag geese (A. anser) showed similar plumages of white, grey, and white with grey patches compared to those in swan geese (A. cygnoides), it was believed the substantial molecular mechanism for plumage variations were different. To date, studies on genes responsible for diverse plumages among graylag geese were limited and causal mutations remain unknown. In this study, genomes from 57 individuals belonging to six breeds showing different plumages were sequenced at ∼10X depth. Firstly, the allele frequency differences (AFD) of variants on the scaffold394 (NW_013185915.1) between grey and white goose breeds (A. anser) was calculated and a genomic region between 768,290-779,889 bp was detected to carry candidate variants associated with plumages, including one SNP (g. 775,151G > T, ∼18.6 kb upstream of EDNRB2) found to be fixed in white geese. This region was overlapped with the one detected by the haplotype-based sweep analysis, in which significant signals defined a candidate region of 736,610-820,622 bp on the same scaffold. Results from the transcriptomic data showed that expression levels of EDNRB2 and many other melanogenesis-related genes were significantly decreased among white geese compared to that in grey geese, especially at late embryonic stages (>E15). Modifications at transcriptional levels might result in abnormal melanocyte developments and thus the white plumages when they grow up. In addition, a frameshift mutation (C > -) in exon4 of MLANA gene on scaffold176 (NW_013185876.1) was suggested as the causal mutation for sex-linked dilution phenotype in graylag geese although this requires more demonstration experiments. Together with observed white plumages caused by EDNRB2 mutations in coding regions among swan geese and chicken, our study provided new examples to study the parallel evolution.