The organic pigments known as carotenoids may be involved in the photosynthesis of ATP in aphids, a paper published in Scientific Reports this week suggests. The study presents what may be the first tentative evidence of ATP photosynthesis in an insect.
Carotenoids occur naturally in the chloroplasts and chromoplasts of plants, algae and some bacteria and fungi, where they have a role in photosynthesis. Unlike other insects, the aphid genome includes genes that encode the proteins needed to synthesize carotenoids, which were probably acquired via lateral gene transfer from fungi. Aphids therefore seem equipped for synthesizing carotenoids, but the potential physiological functions of this system have remained uncertain.
Depending on environmental context, aphids can be manipulated to exhibit different amounts of carotene, which is reflected in their colour. Maria Capovilla, Alain Robichon and colleagues compared orange, green and white aphid strains and found evidence suggesting that carotenoids in orange and green aphids may potentially be involved in absorbing light and using the energy to reduce the co-enzyme NAD+, which can then power ATP synthesis in the mitochondria. The findings hint at an archaic photosynthetic system in aphids, although the mechanisms involved are still uncertain and whether this ability confers a fitness advantage remains to be seen.