Positive phototaxis systems have been well studied in bacteria; however, the photoreceptor(s) and their downstream signaling components that are responsible for negative phototaxis are poorly understood. Negative phototaxis sensory systems are important for cyanobacteria, oxygenic photosynthetic organisms that must contend with reactive oxygen species generated by an abundance of pigment photosensitizers. The unicellular cyanobacterium Synechocystis sp. PCC6803 exhibits type IV pilus-dependent negative phototaxis in response to unidirectional UV-A illumination. Using a reverse genetic approach, together with biochemical, molecular genetic, and RNA expression profiling analyses, we show that the cyanobacteriochrome locus ( slr1212/uirS ) of Synechocystis and two adjacent response regulator loci ( slr1213/uirR and the PatA-type regulator slr1214/lsiR ) encode a UV-A–activated signaling system that is required for negative phototaxis. We propose that UirS, which is membrane-associated via its ETR1 domain, functions as a UV-A photosensor directing expression of lsiR via release of bound UirR, which targets the lsiR promoter. Constitutive expression of LsiR induces negative phototaxis under conditions that normally promote positive phototaxis. Also induced by other stresses, LsiR thus integrates light inputs from multiple photosensors to determine the direction of movement.

Anthocyanin accumulation is regulated negatively by ethylene signaling and positively by sugar and light signaling. However, the antagonistic interactions underlying these signalings remain to be elucidated fully. We show that ethylene inhibits anthocyanin accumulation induced by sucrose (Suc) and light by suppressing the expression of transcription factors that positively regulate anthocyanin biosynthesis, including GLABRA3, TRANSPARENT TESTA8, and PRODUCTION OF AN-THOCYANIN PIGMENT1, while stimulating the concomitant expression of the negative R3-MYB regulator MYBL2. Genetic analyses show that the ethylene-mediated suppression of anthocyanin accumulation is dependent upon ethylene signaling components responsible for the triple response. Furthermore, these positive and negative signaling pathways appear to be under photosynthetic control. Suc and light induction of anthocyanin accumulation was almost fully inhibited in wild-type Arabidopsis (Arabidopsis thaliana) ecotype Columbia and ethylene (ethylene response1 [etr1-1]) and light (long hypocotyl1 [hy1], cryptochrome1/2, and hy5) signaling mutants treated with the photosynthetic electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The transcript level of the sugar transporter gene SUC1 was enhanced in ecotype Columbia treated with the ethylene-binding inhibitor silver and in etr1-1, ethylene insensitive2 (ein2-1), and ein3 ein3-like1 mutants. In contrast, 3-(3,4-dichlorophenyl)-1,1-dimethylurea treatment reduced SUC1 expression, which indicates strongly that SUC1 represents an integrator for signals provided by sugar, light, and ethylene. SUC1 mutations lowered accumulations of anthocyanin pigment, soluble sugar content, and ethylene production in response to Suc and light signals. These data demonstrate that the suppression of SUC1 expression by ethylene inhibits Suc-induced anthocyanin accumulation in the presence of light and, hence, fine-tunes anthocyanin homeostasis.Anthocyanins play key roles in many plant physiological processes; for instance, they form photoprotective screens in vegetative tissue, act as visual attractors to aid pollination and seed dispersal, and function as antimicrobial agents and feeding deterrents in the defense response (Winkel-Shirley, 2001;Steyn et al., 2002). The anthocyanin biosynthetic pathway is well described in plants. In Arabidopsis (Arabidopsis thaliana) and other plants, including Antirrhinum majus (snapdragon) and Petunia hybrida (petunia), early biosynthesis genes (EBGs) such as chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), and flavonoid 3#-hydroxylase (F3#H), which are common to different flavonoid subpathways, are induced prior to late biosynthesis genes (LBGs) such as dihydroflavonol 4-reductase (DFR), leucoanthocyanidin oxygenase (LDOX), anthocyanidin reductase (ANR), and UDP-glucose:flavonoid 3-O-glucosyltransferase (UF3GT; Pelletier et al., 1997). EBGs and LBGs are transcriptionally activated by R2R3-MYBs, such as PRODUCTION OF ANTHOCYANIN PIG-MENT1 (PAP1) a...

The expression of carotenoid biosynthesis genes coding for phytoene synthase (crtB), phytoene desaturase (crtP), -carotene desaturase (crtQ), and ␤-carotene hydroxylase (crtR) is dependent upon light in the cyanobacterium Synechocystis sp. PCC 6803 (Synechocystis). We have demonstrated that the expression of the above four genes was also elevated in the dark-adapted Synechocystis cells upon glucose treatment as a consequence of transcriptional activation. Treatment with glucose analogs such as L-glucose, 3-O-methylglucose, 2-deoxyglucose, and mannose, or inactivation of glucose uptake and phosphorylation by deletion mutation of glucose transporter (glcP) and glucokinase (gk), respectively, did not induce up-regulation of carotenoid genes. When respiratory electron transport or coupling to oxidative phosphorylation was inhibited, glucose induction was not observed, indicating that respiratory electron transport per se is not critical for the expression of these genes. In agreement with this view, the extent of gene expression showed a saturation curve with increasing acridine yellow fluorescence yield, without having a close correlation with the ATP contents or ATP/ADP ratio. The results indicate that glucose induction of carotenoid gene expressions is mediated by an increase in cytosolic pH rather than either redox or glucose sensing.Carotenoids in all photosynthetic organisms including cyanobacteria participate in the light-harvesting process and function in the protection of the photosynthetic apparatus against photo-oxidative damage (1). The cyanobacterium Synechocystis sp. PCC 6803 (hereafter called Synechocystis) contains several genes encoding enzymes involved in carotenoid biosynthesis (2): the crtB gene for phytoene synthase, crtP for phytoene desaturase, crtQ for -carotene desaturase, crtO for ␤-carotene ketolase, and crtR for ␤-carotene hydroxylase.1 Despite an abundance of information about the carotenoid biosynthesis pathway and the genes involved, very little is known about the regulation of the expression of carotenoid biosynthesis genes (3).Light seems to play an important role in the expression of carotenoid biosynthesis genes. In higher plants and green algae, photoreceptors like phytochrome (4, 5) and blue light receptors (6) are involved in light signaling. But, in the cyanobacteria, redox-sensing and signaling by photosynthetic electron transport (7,8) are probably more important than other photosensory systems. This is because the content of carotenoids in Synechococcus sp. PCC 7942 is proportional to the photosynthetic rate (9), and the expression of phytoene synthase (crtB) and phytoene desaturase (crtP) genes in Synechocystis depends upon light intensity (10).To address the redox control over carotenogenesis genes, we took advantage of Synechocystis that grows at the expense of an exogenously supplied sole carbon source, glucose (11). Synechocystis cells uptake external glucose by means of a glucose transporter (glcP, the gene locus sll0771; Ref. 12) and metabolize it further via glycolys...

Background: Cyanobacteriochromes (CBCRs), photoreceptors that sense red to near-UV light, were not previously reported in the cyanobacterium Microcoleus. Results: The Microcoleus genome encodes seven CBCR proteins covalently attached to phycocyanobilin or phycoviolobilin. Conclusion: Near-UV and violet CBCRs are enriched in Microcoleus, whereas red-and green-sensitive CBCRs are absent. Significance: This is the first report of CBCRs in the Microcoleus genome.

No abstract

Angiosperms require light for chlorophyll biosynthesis because one reaction in the pathway, the reduction of protochlorophyllide (Pchlide) to chlorophyllide, is catalyzed by the light-dependent protochlorophyllide oxidoreductase (POR). Here, we report that Cell growth defect factor1 (Cdf1), renamed here as CHAPERONE-LIKE PROTEIN OF POR1 (CPP1), an essential protein for chloroplast development, plays a role in the regulation of POR stability and function. Cdf1/CPP1 contains a J-like domain and three transmembrane domains, is localized in the thylakoid and envelope membranes, and interacts with POR isoforms in chloroplasts. CPP1 can stabilize POR proteins with its holdase chaperone activity. CPP1 deficiency results in diminished POR protein accumulation and defective chlorophyll synthesis, leading to photobleaching and growth inhibition of plants under light conditions. CPP1 depletion also causes reduced POR accumulation in etioplasts of dark-grown plants and as a result impairs the formation of prolamellar bodies, which subsequently affects chloroplast biogenesis upon illumination. Furthermore, in cyanobacteria, the CPP1 homolog critically regulates POR accumulation and chlorophyll synthesis under high-light conditions, in which the dark-operative Pchlide oxidoreductase is repressed by its oxygen sensitivity. These findings and the ubiquitous presence of CPP1 in oxygenic photosynthetic organisms suggest the conserved nature of CPP1 function in the regulation of POR.

, cheol-Ho pan 2 & Youn-il park 1* Like other halophilic cyanobacterial genomes, the de novo-assembled genome of Euhalothece sp. Z-M001 lacks genes encoding keto-carotenoid biosynthesis enzymes, despite the presence of genes encoding carotenoid-binding proteins (cBps). consistent with this, HpLc analysis of carotenoids identified β-carotene and zeaxanthin as the dominant carotenoids. CBPs coexpressed with the zeaxanthin biosynthesis gene increased the survival rates of Escherichia coli strains by preventing antibiotic-induced accumulation of reactive oxygen species (ROS). RNA-seq analysis of Euhalothece revealed that among various salt resistance-related genes, those encoding the na + transporting multiple resistance and pH adaptation (Mrp) systems, glycine betaine biosynthesis enzymes, exopolysaccharide metabolic enzymes, and CBPs were highly upregulated, suggesting their importance in hypersaline habitats. During the early phase of salt deprivation, the amounts of β-carotene and zeaxanthin showed a negative correlation with ROS content. Overall, we propose that in some halophilic cyanobacteria, β-carotene and zeaxanthin, rather than keto-carotenoids, serve as the major chromophores for CBPs, which in turn act as effective antioxidants. Cyanobacteria are photosynthetic prokaryotes that exhibit diverse protective mechanisms to cope with harsh environmental conditions. One of the protective mechanisms involves the use of carotenoids 1 and diverse carotenoid-binding proteins (CBPs) 2 , which play essential roles in protecting the photosynthetic apparatus from damage by both excess light energy and reactive oxygen species (ROS). Most cyanobacterial CBPs bind to β-carotene (β-Car) and its oxygenated derivatives, called xanthophylls (Xan), and are located in photosynthetic protein complexes such as photosystem I (PSI), PSII, and cytochrome b 6 f 3. By contrast, water soluble CBPs bind non-covalently to cyanobacterial keto-carotenoids, such as echinenone (Ech) and canthaxanthin (Can), and to glycosylated-carotenoids such as myxoxanthophyll (Myx) 4 ; CBPs then function as effective energy dissipaters by interacting with the light-harvesting antenna, phycobilisome (PBS) 5. CBPs also bind to zeaxanthin (Zea), albeit with low affinity 6. The orange carotenoid protein (OCP) and its two paralogs, helical carotenoid protein (HCP) and C-terminal domain homolog (CTDH), are the only known soluble CBPs 4. The OCP is composed of two globular domains (one each at the N-and C-terminal ends); a single carotenoid is embedded between the two domains via a hydrophobic interaction 7. Blue light absorption by a keto-carotenoid results in a conformational change in the OCP, from the orange inactive form (OCP°) to the red active form (OCP R). Binding of OCP R to PBS quenches PBS fluorescence, which is prevented by fluorescence recovery protein (FRP) 8. FRP prevents accumulation of the OCP R by interacting with the C-terminal domain of OCP 8. The biological functions of HCPs, which are grouped into nine distinct clades 7 , are largely unknow...

Birds and housingD-old 240 male Ross broilers were randomly allotted to 24 raised wire-floor cages (100×72×50 cm). Temperature was maintained at 32-33°C up to Day 7 and gradually decreased to 22°C at wk 5. A continuous lighting was used for the first 3 d, and 16 h of light and 8 h of darkness were applied until the end of the 5 wk feeding trial. Diets and designThree experimental dietary treatments with eight cages