title: Genetics of the Blue Light-Dependent Signal Cascade That Controls Phototaxis in the Cyanobacterium Synechocystis sp. PCC6803.
abstract: The Synechocystis sp. PCC6803 can move on a solid surface in response to light, a phenomenon called phototaxis. Although many of the photoreceptors involved in phototaxis have been identified, the mechanisms that regulate directional motility of Synechocystis are not well understood. Previous studies showed that a mutant lacking the blue light-using flavin (BLUF) photoreceptor PixD exhibits negative phototaxis under conditions where the wild type responds positively. PixD interacts with the pseudo-response regulator-like protein PixE in a light-dependent manner, suggesting that this intermolecular interaction is important for phototaxis regulation, although genetic evidence has been lacking. To gain further insight into phototaxis regulation by PixD-PixE signaling, we constructed the deletion mutants ΔPixE and ΔPixD-ΔPixE, and characterized their phenotypes, which matched those of the wild type (positive phototaxis). Because ΔPixD exhibited negative phototaxis, PixE must function downstream of PixD. Under intense blue light (>100 μmol m-2 s-1; 470 nm) the wild type exhibited negative phototaxis, but ΔPixD-PixE exhibited positive phototaxis toward low-intensity blue light (∼0.8 μmol m-2 s-1; 470 nm). These results suggest that an unknown light-sensing system(s), that is necessary for directional cell movement, can be activated by low-intensity blue light; on the other hand, PixD needs high-intensity blue light to be activated. We also isolated spontaneous mutants that compensated for the pixE deletion. Genome-wide sequencing of the mutants revealed that the uncharacterized gene sll2003 regulates positive and negative phototaxis in response to light intensity.
authors.affiliation: Graduate School of Bioscience & Biotechnology, Tokyo Institute of Technology, Yokohama, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Sugimoto
authors.affiliation: Graduate School of Bioscience & Biotechnology, Tokyo Institute of Technology, Yokohama, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakamura
authors.affiliation: Center for Biological Resources & Informatics, Tokyo Institute of Technology, Yokohama, USA.
authors.forename: Shukun
authors.initials: S
authors.lastname: Ren
authors.affiliation: Graduate School of Bioscience & Biotechnology, Tokyo Institute of Technology, Yokohama, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Hori
authors.affiliation: Center for Biological Resources & Informatics, Tokyo Institute of Technology, Yokohama, USA.|Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Masuda
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D008027:Light; D055537:Light Signal Transduction / Q000235:genetics / Q000502:physiology; D020283:Photoreceptors, Microbial / Q000235:genetics / Q000378:metabolism; D000071444:Phototaxis / Q000502:physiology*; D046939:Synechocystis / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects*
chemical_list: D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial
keywords:  Blue light receptor; BLUF; Cyanobacteria; Phototaxis; PixD; PixE