How do most birds that are red get their color? Red colouration is the main topic of the in-depth research in the field of evolutionary biology and ecology, where a group of international scientists (including Małgorzata Gazda) presented a newly discovered two genes CYP2J19 and BDH1L.
Red coloration is a salient feature of the natural world. Many vertebrates produce red color by converting dietary yellow carotenoids into red ketocarotenoids via an unknown mechanism. Here, we show that two enzymes, cytochrome P450 2J19 (CYP2J19) and 3-hydroxybutyrate dehydrogenase 1-like (BDH1L), are sufficient to catalyze this conversion. In birds, both enzymes are expressed at the sites of ketocarotenoid biosynthesis (feather follicles and red cone photoreceptors), and genetic evidence implicates these enzymes in yellow/red color variation in feathers. In fish, the homologs of CYP2J19 and BDH1L are required for ketocarotenoid production, and we show that these enzymes are sufficient to produce ketocarotenoids in cell culture and when ectopically expressed in fish skin. Finally, we demonstrate that the red-cone-enriched tetratricopeptide repeat protein 39B (TTC39B) enhances ketocarotenoid production when co-expressed with CYP2J19 and BDH1L. The discovery of this mechanism of ketocarotenoid biosynthesis has major implications for understanding the evolution of color diversity in vertebrates.
The color of the bird’s plumage and its intensity depend on what the birds eat. Carotenoids found in plants play an important role.
The first author of the work, Ph.D. Matthew B. Toomey of the University of Tulsa in the US, was the first to establish that a single CYP2J19 gene, although expressed quite strongly, is not enough to process carotenoids and affect the red color of bird feathers. He looked for genes that have oxidizing properties with oxygen and found two – RDH5 and BDH1L. Further work convinced him that the former is irrelevant in combination with CYP2J19, but the latter is irrelevant.
Next, scientists looked for an answer to the question of the mechanism of action of BDH1L – they wondered if, without linking to another gene, it would cause carotenoids to be processed.
The experiment was repeated. It turned out that the cells converted the carotenoids to epsiloncarotenoids – another type of carotenoids that birds with yellow plumage have in abundance.
It turns out that carotenoids are responsible not only for the color of feathers, but also the types of receptors in the eyes.
“The lack of red pigment in the irises is likely to make some birds see differently,” said Małgorzata Gazda from The Institut Pasteur, an internationally renowned center for biomedical research.
The researchers also looked at pigments found in fish – zebrafish. It turned out that analogous genes are responsible for their occurrence. The scientists confirmed in their work that the same genes and the same mechanisms exist in species even very distant from each other along the evolutionary path – in this case – in birds and in fish.
“It looks like this biochemical pathway could be a universal mechanism by which vertebrates can become red in color,” said Gazda.
In the study, scientists used six species of birds: domestic hen, diamond firetail, star finch, red-eared parrotfinch, northern cardinal, red siskin and a fish – zebrafish.