Abstract :
[en] The F2 duck populations derived from Liancheng Ducks and Pekin Ducks exhibit high nutritional meat quality and large size bodies, while they are segregated by feather color. Our goal is to rapidly produce high-quality meat ducks characterized by white feathers and black beaks, traits associated with premium meat production. Traditional breeding methods are insufficient for achieving this goal efficiently, as they cannot reliably produce ducks with the desired phenotype nor ensure heterozygous genotypes. This limitation also prevents us from protecting our research through patenting. Therefore, this PhD looks at revealing causative genes for unique plumage phenotype in Liancheng ducks. The purpose is three-fold: (1) to identify the melanin deposition in different tissues of the Liancheng and other ducks, (2) to explore the genetic mechanism of white plumage in Liancheng ducks, (3) to apply the molecular markers explored in this study to expedite the genetic breeding of high-quality meat ducks.
Firstly, 9 ducks, Mallards (n=3), Liancheng (n=3) and Pekin ducks (n=3), were examined by high performance liquid chromatography (HPLC) and Masson-Fontana staining to reveal the difference of feather melanin content. Pectoral, skin, liver, fat, brain, heart, kidney, lung, and spleen tissue of 8-week-old black-feathered ducks were collected to identify candidate genes by analyzing their expression levels. The results showed that the melanin content in feathers, beak, and web of Liancheng ducks were higher than that in Pekin ducks (p<0.05). Melanin within hair follicle was located in the barb ridge and hair matrix of black feathered ducks. This study firstly revealed the unique feather color phenotype of Liancheng ducks, and highlighted variations in the expression of candidate genes involved in the melanin formation pathways across different tissues and developmental stages.
Secondly, 1.29 Gb of the Liancheng duck genome was assembled involving a contig N50 of 12.17 Mb and a scaffold N50 of 83.98 Mb. Beyond the epistatic effect of the MITF gene, GWAS analysis pinpointed a 0.8Mb genomic region encompassing the PMEL gene. This gene encoded a protein specific to pigment cells and was essential for the formation of fibrillar sheets within melanosomes, the organelles responsible for pigmentation. Additionally, Dual-luciferase reporter analysis revealed two candidate SNPs (Chr33:5,303,994A>G; 5,303,997A>G) that might alter PMEL transcription, potentially influencing plumage coloration in Liancheng ducks. Our study assembled the reference genome of Liancheng ducks, and presented compelling evidence that the white plumage characteristic of this breed was attributable to the PMEL gene, previously regarded as a “missing gene” in ducks.
At last, we used the two molecular SNP markers to carry out a hybridization experiment. In this experiment, first, 1 bbrr genotype male, that was white-feathered and had a yellow beak, was crossbred with 8 BBrr genotype females, all white-feathered and with black beaks. All 56 Bbrr commercial descendants (F1 generation) were white-feathered, with black beaks. After continued hybridization of the F1 individuals, the phenotypes and proportions of the 224 F2 offspring were in line with our expectations. Specifically, this included 61 bbrr genotype ducks with white feathers and yellow beaks and 163 B_rr genotype ducks with white feathers and black beaks, adhering to the Mendelian ratio of 1:3. Then, 30 Pekin ducks were crossbred with 120 Liancheng ducks, 602 F2 blood samples of the white-feathered yellow beak ducks from the F2 population were collected and 153 bbrr genotype ducks with white feathers and yellow beaks were successfully selected. In the future, these 153 ducks will be crossbred with BBrr white-feathered black beak ducks to produce Bbrr white-feathered black beak ducks. We thus have successfully developed a comprehensive system solution for the breeding of high-quality duck breeds.
In summary, this thesis sheds light on the complex mechanisms of underlying the identification of causative genes for the unique plumage phenotype in Liancheng ducks and offers valuable insights and direction for future research and breeding programs aimed at understanding and influencing avian plumage coloration.
