Function of the Polyketide synthase 1-like gene is required for yellow feather pigmentation in Rose-ringed and Alexandrine parakeet

Parrots are the only species on earth known to produce psittacofulvin pigments and the expression of these pigments is controlled genetically and not environmentally. Unlike carotenoids, psittacofulvins do not come from dietary sources, suggesting that they are produced by an uncharacterized biochemical pathway. In budgerigar (Melopsittacus undulatus), the recessive Mendelian "blue" trait abolishes yellow pigmentation. Recently, it was demonstrated that a single amino acid substitution (R644W) in the uncharacterized Polyketide synthase 1-like gene (MuPKS) interrupts the biochemical pathway for psittacofulvin synthesis and responsible for the "blue" trait in budgerigar. To test whether mutations in PKS, is responsible for the "blue" trait in other parrots species, we have decided to further characterize the function of PKS enzyme in Rose-ringed parakeet (Psittacula krameri) and Alexandrine parakeet (Psittacula eupatria). First, we identified and sequenced the PKS gene in both the parakeets and found that they share 96% similarity with MuPKS at protein level. Next, we sequenced the gene in "blue" mutants and found that each species has a unique nonsense mutation [c.2005G>T (p.E668X) in P. krameri and c.2647A>T (p.L882X) in P. eupatria]. Moreover, through genomic analysis we found an additional missense mutation c.728G>A; p.R243K in P. eupatria. We aimed to express these putative genes heterologously in yeast to carry out their structural and functional analysis. This study focuses on expanding the knowledge of genetic control and the biochemical basis of different plumage color traits in family Psittaculidae.