Distribution and phylogeny of the blue light receptors aureochromes in eukaryotes

The new type blue light (BL) receptor aureochrome (AUREO) was recently discovered in a stramenopile alga, Vaucheria (Takahashi et al. Proc Natl Acad Sci USA 104(49):19625-19630, 2007). AUREO has a bZIP (basic region/leucine zipper) and BL-sensing light-oxygen-voltage (LOV) domain and functions as a BL-activated transcription factor. It mediates BL-induced branching and regulates the development of the sex organ in V. frigida. Although AUREO sequences have previously been found in Fucus and some diatoms, here we report that AUREO orthologs are commonly conserved in photosynthetic stramenopiles. Five AUREO orthologs were isolated from three stramenopile genera (Fucus, Ochromonas, and Chattonella). By BLAST search, several AUREO sequences were also detected in genomes in Aureococcus anophagefferens (Pelagophyceae). However, AUREO was not found in heterotrophic stramenopiles or in closely related phyla, such as haptophytes and cryptophytes, or in green plants. Stramenopiles do not possess phototropin, the well-known BL receptor for phototropism of green plants. From comparative analysis of LOV domains, together with kinship analysis of AUREO bZIP domains, AUREO can be regarded as the BL receptor specific to phototrophic stramenopiles. The evolution of AUREO and the phylogeny of LOV domains in stramenopiles and green plants are discussed.