Mutation in SLC45A2 leads to loss of melanin in parrot feathers

Bird plumage coloration is a complex and multi-factorial process that involves both genetic and environmental factors. Diverse pigment groups contribute to plumage variation in different birds. In parrots, the predominant green color results from the combination of two different primary colors-yellow and blue. Psittacofulvin, a pigment uniquely found in parrots, is responsible for the yellow coloration, while blue is suggested to be the result of light scattering by feather nanostructures and melanin granules. So far, genetic control of melanin-mediated blue coloration has been elusive. In this study, we demonstrated that feather from the yellow mutant rose-ringed parakeet displays loss of melanosome granules in spongy layer of feather barb. Using whole genome sequencing, we found that mutation in SLC45A2, an important solute carrier protein in melanin synthetic pathway, is responsible for the sex-linked yellow phenotype in rose-ringed parakeet. Intriguingly, one of the mutations, P53L found in yellow P. krameri is already reported as P58A/S in the human albinism database, known to be associated with human OCA4. We further showed that mutations in SLC45A2 gene affect melanin production also in other members of Psittaculidae family such as alexandrine, and plum-headed parakeets. Additionally, we demonstrate that the mutations associated with the sex-linked yellow phenotype, localized within the transmembrane domains of the SLC45A2 protein, affect the protein localization pattern. This is the first evidence of plumage color variation involving SLC45A2 in parrots and confirmation of associated mutations in the transmembrane domains of the protein that affect its localization. Article SummaryThe vibrant green tone of parrot plumage emerges from a blend of yellow and blue. While yellow comes from a unique pigment psittacofulvin, the genetics of blue structural color has puzzled scientists. Through novel genetic study, here we identified mutations in SLC45A2 gene, causing loss of melanin in feathers that contributes to the blue structural color. This insight opens a new chapter in understanding avian coloration and the complex interplay of feather microstructure and genetics in natures palette.