Genetic Basis for Red Coloration in Birds

Area of Science:

• Genetics
• Evolutionary Biology
• Biochemistry

Background:

• Bird feather color, particularly red, is crucial for social signaling and mate selection.
• Birds produce red pigments by converting yellow carotenoids through an endogenous oxidation process.
• The enzyme catalyzing this critical conversion, a ketolase, was previously unidentified.

Purpose of the Study:

• To investigate the genetic underpinnings of red feather coloration in avian species.
• To identify the specific gene(s) responsible for the endogenous conversion of carotenoids into red pigments.
• To explore the role of this pathway in other physiological functions, such as vision.

Main Methods:

• Whole-genome sequencing of red siskins, common canaries, and hybrid red factor canaries.
• Analysis of introgressed genomic regions associated with red coloration.
• Transcriptome analysis to assess gene expression levels in relevant tissues (skin, liver).

Main Results:

• Two introgressed genomic regions from red siskins were identified as essential for red coloration in hybrid canaries.
• The gene CYP2J19, encoding a cytochrome P450 enzyme, was found within one region and significantly upregulated in red factor canaries.
• Evidence suggests CYP2J19 functions as the key ketolase for red pigment synthesis and is also involved in retinal ketocarotenoid formation.

Conclusions:

• CYP2J19 is identified as the carotenoid ketolase responsible for red feather pigmentation in birds.
• The genetic basis for red coloration involves introgression of specific genomic regions, including the CYP2J19 gene.
• This discovery provides insights into the evolution of signaling traits and the biochemical pathways underlying carotenoid metabolism.