Multiple mutations in polyketide synthase led to disruption of Psittacofulvin production across diverse parrot species

Polyketide synthases (PKSs) are crucial multidomain enzymes in diverse natural product biosynthesis. Parrots use a type I PKS to produce a unique pigment called psittacofulvin in their feathers. In domesticated budgerigars and lovebirds, the same amino acid substitution (R644W) within malonyl/acetyltransferase (MAT) domain of this enzyme has been shown to cause the blue phenotype with no psittacofulvin pigmentation, proposing a strong evolutionary constraint mechanism. Here, we identified six new causal variants in PKS associated with defective psittacofulvin production in four diverse species, including three nonsense mutations. Remaining three nonsynonymous substitutions reside within the ketoacyl synthase (KS) domain. Heterologous expression of these PKS variants in yeast confirmed complete or reduced loss of psittacofulvin production, additionally suggesting presence of an auxiliary polymorphism at the MAT domain. Our findings establish PKS as a functionally conserved key-enzyme determining psittacofulvin-based hues among diverse parrots, highlighting multiple conserved domains essential for the PKS function.