title: Complementation of phytochrome chromophore-deficient Arabidopsis by expression of phycocyanobilin:ferredoxin oxidoreductase.
abstract: The covalently bound phytochromobilin (PphiB) prosthetic group is required for the diverse photoregulatory activities of all members of the phytochrome family in vascular plants, whereas by contrast, green algal and cyanobacterial phytochromes use the more reduced linear tetrapyrrole pigment phycocyanobilin (PCB). To assess the functional consequence of the substitution of PphiB with PCB in plants, the phytochrome chromophore-deficient hy2 mutant of Arabidopsis was transformed with a constitutively expressed pcyA gene that encodes the cyanobacterial enzyme, PCB:ferredoxin oxidoreductase. Spectroscopic analyses of extracts from etiolated seedlings revealed that PcyA expression restored photoactive phytochrome to WT levels, albeit with blue-shifted absorption maxima, while also restoring light lability to phytochrome A. Photobiological measurements indicated that PcyA expression rescued phytochrome-mediated red high-irradiance responses, low-fluence red/far-red (FR) photoreversible responses, and very-low-fluence responses, thus confirming that PCB can functionally substitute for PphiB for these photoregulatory activities. Although PcyA expression failed to rescue phytochrome A-mediated FR high-irradiance responsivity to that of WT, our studies indicate that the FR high-irradiance response is fully functional in pcyA-expressing plants but shifted to shorter wavelengths, indicating that PCB can functionally complement this phytochrome-mediated response in vascular plants.
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan.
authors.forename: Chitose
authors.initials: C
authors.lastname: Kami
authors.forename: Keiko
authors.initials: K
authors.lastname: Mukougawa
authors.forename: Takuya
authors.initials: T
authors.lastname: Muramoto
authors.forename: Akiho
authors.initials: A
authors.lastname: Yokota
authors.forename: Tomoko
authors.initials: T
authors.lastname: Shinomura
authors.forename: J Clark
authors.initials: JC
authors.lastname: Lagarias
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kohchi
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D001483:Base Sequence; D017931:DNA Primers; D005816:Genetic Complementation Test; D010088:Oxidoreductases / Q000235:genetics*; D010834:Phytochrome / Q000235:genetics*; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D013053:Spectrophotometry
chemical_list: D017931:DNA Primers; D010834:Phytochrome; D010088:Oxidoreductases