A chimeric photoreceptor gene, NEOCHROME, has arisen twice during plant evolution.

Abstract

Although most plant species from algae to flowering plants use blue light for inducing phototropism and chloroplast movement, many ferns, some mosses, and green algae use red as well as blue light for the regulation of these responses, resulting in better sensitivity at low light levels. During their evolution, ferns have created a chimeric photoreceptor (phy3 in Adiantum) between phytochrome (phy) and phototropin (phot) enabling them to use red light effectively. We have identified two genes resembling Adiantum PHY3, NEOCHROME1 and NEOCHROME2 (MsNEO1 and MsNEO2), in the green alga Mougeotia scalaris, a plant famous for its light-regulated chloroplast movement. Like Adiantum PHY3, both MsNEO gene products show phytochrome-typical bilin binding and red/far-red reversibility, the difference spectra matching the known action spectra of light-induced chloroplast movement in Mougeotia. Furthermore, both genes rescue red-light-induced chloroplast movement in Adiantum phy3 mutants, indicating functional equivalence. However, the fern and algal genes seem to have arisen independently in evolution, thus providing an intriguing example of convergent evolution.