Photosynthesis Gene Expression Research Articles

Exogenous glutathione improves high root-zone temperature tolerance by modulating photosynthesis, antioxidant and osmolytes systems in cucumber seedlings.

To investigate the physiological responses of plants to high root-zone temperature (HT, 35 °C) stress mitigated by exogenous glutathione (GSH), cucumber (Cucumis sativus L.) seedlings were exposed to HT with or without GSH treatment for 4 days and following with 4 days of recovery. Plant physiological variables, growth, and gene expression related to antioxidant enzymes and Calvin cycle were quantified. The results showed that HT significantly decreased GSH content, the ratio of reduced to oxidized glutathione (GSH/GSSG), chlorophyll content, photosynthesis and related gene expression, shoot height, stem diameter, as well as dry weight. The exogenous GSH treatment clearly lessened the HT stress by increasing the above variables. Meanwhile, HT significantly increased soluble protein content, proline and malondialdehyde (MDA) content as well as O2•− production rate, the gene expression and activities of antioxidant enzymes. The GSH treatment remarkably improved soluble protein content, proline content, antioxidant enzymes activities, and antioxidant enzymes related gene expression, and reduced the MDA content and O2•− production rate compared to no GSH treatment in the HT condition. Our results suggest that exogenous GSH enhances cucumber seedling tolerance of HT stress by modulating the photosynthesis, antioxidant and osmolytes systems to improve physiological adaptation.

Effects of 2,4-epibrassinolide on photosynthesis and Rubisco activase gene expression in Triticum aestivum L. seedlings under a combination of drought and heat stress

We examined the effects of 2,4-epibrassinolide (EBR) application on photosynthesis, antioxidant enzyme activity, and Rubisco activase (RCA) gene expression in wheat (Triticum aestivum L.) seedlings under a combination of drought and heat stress. The net photosynthetic rates (Pn) of wheat seedlings decreased significantly, the photosynthetic capability was inhibited, and the activities of superoxide (SOD), peroxidase (POD), catalase (CAT), and RCA as well as the initial and total activity of Rubisco declined under the combined stress. These decreases and inhibitory effects were significantly ameliorated by exogenous EBR application. Three subunits (45–46, 41–42, and 38–39 kDa) of RCA were observed in wheat seedlings. The abundances of the 38–39 kDa and 41–42 kDa subunits were significantly lower in plants subjected to stressful conditions than in unstressed plants. Interestingly, a marked increase in 45–46 kDa RCA was observed under heat or heat combined with drought stress. The abundance of 38–39 kDa RCA in seedlings exposed to heat, drought, or their combination was significantly enhanced by EBR pretreatment, which paralleled the changes in initial Rubisco activity and Pn, but was not consistent with observed mRNA abundance. These results indicated that the larger subunit of RCA (45–46 kDa), which is more thermostable and increased in response to moderate heat stress, and the smaller isoform (38–39 kDa) of RCA may play important roles in maintaining the photosynthetic capability by EBR under stress conditions.

Identification and Comparative Analysis of Differential Gene Expression in Soybean Leaf Tissue under Drought and Flooding Stress Revealed by RNA-Seq.

Drought and flooding are two major causes of severe yield loss in soybean worldwide. A lack of knowledge of the molecular mechanisms involved in drought and flood stress has been a limiting factor for the effective management of soybeans; therefore, it is imperative to assess the expression of genes involved in response to flood and drought stress. In this study, differentially expressed genes (DEGs) under drought and flooding conditions were investigated using Illumina RNA-Seq transcriptome profiling. A total of 2724 and 3498 DEGs were identified under drought and flooding treatments, respectively. These genes comprise 289 Transcription Factors (TFs) representing Basic Helix-loop Helix (bHLH), Ethylene Response Factors (ERFs), myeloblastosis (MYB), No apical meristem (NAC), and WRKY amino acid motif (WRKY) type major families known to be involved in the mechanism of stress tolerance. The expression of photosynthesis and chlorophyll synthesis related genes were significantly reduced under both types of stresses, which limit the metabolic processes and thus help prolong survival under extreme conditions. However, cell wall synthesis related genes were up-regulated under drought stress and down-regulated under flooding stress. Transcript profiles involved in the starch and sugar metabolism pathways were also affected under both stress conditions. The changes in expression of genes involved in regulating the flux of cell wall precursors and starch/sugar content can serve as an adaptive mechanism for soybean survival under stress conditions. This study has revealed the involvement of TFs, transporters, and photosynthetic genes, and has also given a glimpse of hormonal cross talk under the extreme water regimes, which will aid as an important resource for soybean crop improvement.

Physiological and molecular evidence of differential short-term heat tolerance in Mediterranean seagrasses.

The increase in extreme heat events associated to global warming threatens seagrass ecosystems, likely by affecting key plant physiological processes such as photosynthesis and respiration. Understanding species’ ability to acclimate to warming is crucial to better predict their future trends. Here, we study tolerance to warming in two key Mediterranean seagrasses, Posidonia oceanica and Cymodocea nodosa. Stress responses of shallow and deep plants were followed during and after short-term heat exposure in mesocosms by coupling photo-physiological measures with analysis of expression of photosynthesis and stress-related genes. Contrasting tolerance and capacity to heat acclimation were shown by shallow and deep P. oceanica ecotypes. While shallow plants acclimated through respiratory homeostasis and activation of photo-protective mechanisms, deep ones experienced photosynthetic injury and impaired carbon balance. This suggests that P. oceanica ecotypes are thermally adapted to local conditions and that Mediterranean warming will likely diversely affect deep and shallow meadow stands. On the other hand, contrasting mechanisms of heat-acclimation were adopted by the two species. P. oceanica regulates photosynthesis and respiration at the level of control plants while C. nodosa balances both processes at enhanced rates. These acclimation discrepancies are discussed in relation to inherent attributes of the two species.

Members of the PpaA/AerR Antirepressor Family Bind Cobalamin.

PpaA from Rhodobacter sphaeroides is a member of a family of proteins that are thought to function as antirepressors of PpsR, a widely disseminated repressor of photosystem genes in purple photosynthetic bacteria. PpaA family members exhibit sequence similarity to a previously defined SCHIC (sensor containing heme instead of cobalamin) domain; however, the tetrapyrrole-binding specificity of PpaA family members has been unclear, as R. sphaeroides PpaA has been reported to bind heme while the Rhodobacter capsulatus homolog has been reported to bind cobalamin. In this study, we reinvestigated tetrapyrrole binding of PpaA from R. sphaeroides and show that it is not a heme-binding protein but is instead a cobalamin-binding protein. We also use bacterial two-hybrid analysis to show that PpaA is able to interact with PpsR and activate the expression of photosynthesis genes in vivo. Mutations in PpaA that cause loss of cobalamin binding also disrupt PpaA antirepressor activity in vivo. We also tested a number of PpaA homologs from other purple bacterial species and found that cobalamin binding is a conserved feature among members of this family of proteins. Cobalamin (vitamin B12) has only recently been recognized as a cofactor that affects gene expression by interacting in a light-dependent manner with transcription factors. A group of related antirepressors known as the AppA/PpaA/AerR family are known to control the expression of photosynthesis genes in part by interacting with either heme or cobalamin. The specificity of which tetrapyrroles that members of this family interact with has, however, remained cloudy. In this study, we address the tetrapyrrole-binding specificity of the PpaA/AerR subgroup and establish that it preferentially binds cobalamin over heme.

Evidence that Altered Cis Element Spacing Affects PpsR Mediated Redox Control of Photosynthesis Gene Expression in Rubrivivax gelatinosus.

PpsR is a major regulator of photosynthesis gene expression among all characterized purple photosynthetic bacteria. This transcription regulator has been extensively characterized in Rhodobacter (Rba.) capsulatus and Rba. sphaeroides which are members of the α-proteobacteria lineage. In this study, we have investigated the biochemical properties and mutational effects of a ppsR deletion strain in the β-proteobacterium Rubrivivax (Rvi.) gelatinosus in order to reveal phylogenetically conserved mechanisms and species-specific characteristics. A deletion of the ppsR gene resulted in de-repression of photosystem synthesis showing that PpsR functions as a repressor of photosynthesis genes in this species. We also constructed a Rvi. gelatinosus PpsR mutant in which a conserved cysteine at position 436 was changed to an alanine to examine whether or not this residue is important for sensing redox, as reported in Rhodobacter species. Surprisingly, the Cys436 Ala mutant retained the ability to repress photosynthesis gene expression under aerobic conditions, suggesting that PpsR from Rvi. gelatinosus has different redox-responding characteristics. Furthermore, biochemical analyses demonstrated that Rvi. gelatinosus PpsR only shows redox-dependent binding to promoters with 9-bp spacing, but not 8-bp spacing, between two PpsR-recognition sequences. These results indicate that redox-dependent binding of PpsR requires appropriate cis configuration of PpsR target sequences in Rvi. gelatinosus. These results also indicate that PpsR homologs from different species regulate photosynthesis genes with altered biochemical properties.

Effects of exogenous 5-aminolevulinic acid on photosynthesis, stomatal conductance, transpiration rate, and PIP gene expression of tomato seedlings subject to salinity stress.

The effects of exogenous 5-aminolevulinic acid (ALA) on photosynthesis, plant growth, and the expression of two aquaporin genes in tomato seedlings under control and salinity conditions were investigated. Exogenous ALA application significantly improved net photosynthetic rate (Pn), total chlorophyll content, and plant biomass accumulation of tomato seedlings under salinity stress. As revealed by real-time PCR analyses, after treatment with ALA alone, expression of both LePIP1 and LePIP2 in the two tomato cultivars was up-regulated at 2 h and subsequently decreased to normal levels. Under salinity stress, transcript levels of LePIP1 in both leaves and roots of salt-sensitive cultivars (cv. Zhongza No.9) increased significantly and were considerably higher than in cultivars exposed to ALA alone. In contrast, the expression levels of LePIP1 and LePIP2 in cvs. Jinpeng No.1 cultivars were slightly lower under salinity stress than under ALA treatment. In addition, transcript levels of both LePIP1 and LePIP2 in the roots of Jinpeng No. 1 cultivars were considerably lower than those in the roots of Zhongza No. 9 cultivars under salinity stress, regardless of ALA supplementation, implying that Jinpeng No. 1 cultivars had a better capacity to maintain membrane intrinsic protein stability. Further, ALA application distinctly counteracted the up- or down-regulation of LePIP1 and LePIP2 in both cultivars under salinity stress, in accordance with the improvements instomatal conductance, transpiration rate, and Pn of tomato leaves. The results presented here indicate that ALA controls aquaporin expression, thus, presumably ALA regulates water homeostasis and enhances salt tolerance of tomato seedlings.

Expression analysis of photosynthesis genes in Dunaliella salina grown at different NaCl concentrations

The expression of five genes involved in photosynthesis was investigated under different salinity conditions in Dunaliella salina. These genes encodes ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) large and small subunits, major light-harvesting chlorophyll (chl) a/b protein of photosystem II, carbonic anhydrase and adenosine tri phosphate synthase alpha subunit. As D. salina grows in hypersaline conditions, it is important to study expression of these genes in relation to different salinity levels. Changes in the mRNA level under different NaCl conditions were determined using the comparative CT method. Cell number and chl a content were estimated to determine optimal growth at different NaCl concentrations. Real-time PCR results showed enhanced expression of photosynthesis genes upon exposure of D. salina cells from Sambhar Lake to 1.7 M NaCl containing medium. This salinity corresponds to only one-third of the salinity of the Sambhar Lake habitat. In another salt condition, the expression level of all genes was found to be down -regulated at 1.0 M (sub-optimal concentration for growth of D. salina), 2.5 M and 3.0 M NaCl (supra-optimal concentration for growth) when compared with 1.7 M NaCl containing medium as a control. The present study will help in understanding the salinity tolerance in D. salina as a model microalga.

The Growth Zone of Maize Leaves is an Ideal Model System for Systems Biology Approaches to Investigate the Effects of Drought Stress on Organ Growth Regulation

Drought is the most important yield-limiting factor under natural and agricultural conditions and therefore detailed knowledge of its impact on plant growth regulation is crucial. The maize leaf represents an attractive system for growth studies, because of its spatial gradient, allowing sampling of dividing, expanding and mature cells at the same time, and its big size, providing enough material for molecular analyses: a big advantage over the model plant Arabidopsis thaliana.By means of a kinematic analysis we showed that drought inhibits leaf growth by reducing cell division rates in the meristem and cell expansion rates in the elongation zone. A transcriptome analysis provided a molecular basis for the observed inhibition of cell division rates, but also pointed at distinct effects on the development of the photosynthetic machinery, and antioxidant and redox systems. The effects on these pathways were subsequently confirmed by detailed biochemical analysis of the activity of key enzymes and quantification of metabolites.We demonstrated the functional significance of the identified transcriptional and physiological changes, showing that 1. Increasing the antioxidant capacity in the growth zone, by overexpression of iron superoxide dismutase, increases leaf growth under control and drought conditions. 2. Increased expression of photosynthesis genes under stress facilitates faster growth upon re-watering compared to unstressed controls.

Dynamic composition, shaping and organization of plastid nucleoids.

In this article recent progress on the elucidation of the dynamic composition and structure of plastid nucleoids is reviewed from a structural perspective. Plastid nucleoids are compact structures of multiple copies of different forms of ptDNA, RNA, enzymes for replication and gene expression as well as DNA binding proteins. Although early electron microscopy suggested that plastid DNA is almost free of proteins, it is now well established that the DNA in nucleoids similarly as in the nuclear chromatin is associated with basic proteins playing key roles in organization of the DNA architecture and in regulation of DNA associated enzymatic activities involved in transcription, replication, and recombination. This group of DNA binding proteins has been named plastid nucleoid associated proteins (ptNAPs). Plastid nucleoids are unique with respect to their variable number, genome copy content and dynamic distribution within different types of plastids. The mechanisms underlying the shaping and reorganization of plastid nucleoids during chloroplast development and in response to environmental conditions involve posttranslational modifications of ptNAPs, similarly to those changes known for histones in the eukaryotic chromatin, as well as changes in the repertoire of ptNAPs, as known for nucleoids of bacteria. Attachment of plastid nucleoids to membranes is proposed to be important not only for regulation of DNA availability for replication and transcription, but also for the coordination of photosynthesis and plastid gene expression.

Plastid encoded RNA polymerase activity and expression of photosynthesis genes required for embryo and seed development in Arabidopsis.

Chloroplast biogenesis and function is essential for proper plant embryo and seed development but the molecular mechanisms underlying the role of plastids during embryogenesis are poorly understood. Expression of plastid encoded genes is dependent on two different transcription machineries; a plastid-encoded bacterial-type RNA polymerase (PEP) and a nuclear-encoded phage-type RNA polymerase (NEP), which recognize distinct types of promoters. However, the division of labor between PEP and NEP during plastid development and in mature chloroplasts is unclear. We show here that PLASTID REDOX INSENSITIVE 2 (PRIN2) and CHLOROPLAST STEM-LOOP BINDING PROTEIN 41 kDa (CSP41b), two proteins identified in plastid nucleoid preparations, are essential for proper plant embryo development. Using Co-IP assays and native PAGE we have shown a direct physical interaction between PRIN2 and CSP41b. Moreover, PRIN2 and CSP41b form a distinct protein complex in vitro that binds DNA. The prin2.2 and csp41b-2 single mutants displayed pale phenotypes, abnormal chloroplasts with reduced transcript levels of photosynthesis genes and defects in embryo development. The respective csp41b-2prin2.2 homo/heterozygote double mutants produced abnormal white colored ovules and shrunken seeds. Thus, the csp41b-2prin2.2 double mutant is embryo lethal. In silico analysis of available array data showed that a large number of genes traditionally classified as PEP dependent genes are transcribed during early embryo development from the pre-globular stage to the mature-green-stage. Taken together, our results suggest that PEP activity and consequently the switch from NEP to PEP activity, is essential during embryo development and that the PRIN2-CSP41b DNA binding protein complex possibly is important for full PEP activity during this process.

Analysis of Effects of Berberine on the Photosynthesis of Microcystis aeruginosa at Gene Transcriptional Level

AbstractMicrocystis aeruginosa has great competition advantages to survive, grow, and dominate phytoplankton communities for its high photosynthetic activity in unsuitable conditions. Berberine was the allelochemical capable of inhibiting M. aeruginosa growth. To better understand the allelopathic mechanism involved, RNA‐sequencing technology was used to investigate the berberine‐induced changes in photosynthesis gene expression of M. aeruginosa. Using the next‐generation sequencing platform Illumina/Solexa, a total of 13 099 868 and 13 870 448 90‐bp pair‐end reads for “no berberine” and “berberine” libraries were obtained, respectively. Among these genes, 10 324 794 (no berberine) and 8 944 254 (berberine) reads mapped multiply in the genome, while 9 988 318 (no berberine) and 8 316 668 (berberine) mapped to unique targets, respectively. It was indicated that berberine significantly repressed the expression of 869 genes and induced the expression of 1419 genes. Those berberine‐affected genes belonged to different functional categories, especially enriched in various photosynthesis‐relevant metabolic pathways based on the analysis of gene ontology, clusters of orthologous group terms, and Kyoto Encyclopedia of Genes and Genomes. The results suggested that berberine‐induced disturbance in the algal photosynthesis process via repressing the expression of key photosynthesis genes, such as psbD, psaA, psaB, might be one of the main mechanisms involved in inhibitory allelopathic activity of berberine.

Effects of high temperature on photosynthesis and related gene expression in poplar.

BackgroundHigh temperature, whether transitory or constant, causes physiological, biochemical and molecular changes that adversely affect tree growth and productivity by reducing photosynthesis. To elucidate the photosynthetic adaption response and examine the recovery capacity of trees under heat stress, we measured gas exchange, chlorophyll fluorescence, electron transport, water use efficiency, and reactive oxygen-producing enzyme activities in heat-stressed plants.ResultsWe found that photosynthesis could completely recover after less than six hours of high temperature treatment, which might be a turning point in the photosynthetic response to heat stress. Genome-wide gene expression analysis at six hours of heat stress identified 29,896 differentially expressed genes (15,670 up-regulated and 14,226 down-regulated), including multiple classes of transcription factors. These interact with each other and regulate the expression of photosynthesis-related genes in response to heat stress, controlling carbon fixation and changes in stomatal conductance. Heat stress of more than twelve hours caused reduced electron transport, damaged photosystems, activated the glycolate pathway and caused H2O2 production; as a result, photosynthetic capacity did not recover completely.ConclusionsThis study provides a systematic physiological and global gene expression profile of the poplar photosynthetic response to heat stress and identifies the main limitations and threshold of photosynthesis under heat stress. It will expand our understanding of plant thermostability and provides a robust dataset for future studies.

Differential soybean gene expression during early phase of infection with Mungbean yellow mosaic India virus.

Mungbean yellow mosaic India virus (MYMIV), a bipartite begomovirus, causes yellow mosaic disease to soybean. Studies related to host gene expression in response to begomovirus infection have mostly been performed with systemically infected tissues at a later period of infection. In this study, soybean gene expression analysis has been performed to understand local responses against MYMIV at an early stage of infection before appearance of detectable limit of late viral transcripts. 444 soybean transcripts belonging to eleven functional categories showed significant changes in expression level at two days after infection. MYMIV infection resulted in enhanced expression of genes associated with hypersensitive response, programmed cell death and resistance response pathways and reduced expression of genes for photosynthesis and sugar transport. Comparative expression analysis of selected transcripts in the susceptible and a resistant variety displayed differential expression of host genes involved in intercellular virus movement and long distance signaling of systemic acquired resistance.

Influence of tris(2,3-dibromopropyl) isocyanurate on the expression of photosynthesis genes of Nannochloropsis sp.

The proteins encoded by psaA and psaB form a heterodimer, an essential compound of photosystem; while the protein encoded by psbC binds with chlorophyll a in photosystem II, serving as antennae in photosystem. Here we report that a heterocyclic brominated flame retardant, tris(2,3-dibromopropyl) isocyanurate (TBC), inhibited the expression of psaA and psbC, then leads to the decrease of Nannochloropsis sp.'s growth biomass. TBC exposure inhibited the expression of psaA and psbC at 10, 100ng/mL slightly and 1000ng/mL significantly. In addition, TBC was found to slow down the growth of Nannochloropsis sp. at concentrations ranging from 10 to 1000ng/mL. These results indicated that TBC influenced both photosynthesis and growth performance of Nannochloropsis sp.

PHYTOCHROME INTERACTING FACTOR3 Associates with the Histone Deacetylase HDA15 in Repression of Chlorophyll Biosynthesis and Photosynthesis in EtiolatedArabidopsisSeedlings

PHYTOCHROME INTERACTING FACTOR3 (PIF3) is a key basic helix-loop-helix transcription factor of Arabidopsis thaliana that negatively regulates light responses, repressing chlorophyll biosynthesis, photosynthesis, and photomorphogenesis in the dark. However, the mechanism for the PIF3-mediated transcription regulation remains largely unknown. In this study, we found that the REDUCED POTASSIUM DEPENDENCY3/HISTONE DEACETYLASE1-type histone deacetylase HDA15 directly interacted with PIF3 in vivo and in vitro. Genome-wide transcriptome analysis revealed that HDA15 acts mainly as a transcriptional repressor and negatively regulates chlorophyll biosynthesis and photosynthesis gene expression in etiolated seedlings. HDA15 and PIF3 cotarget to the genes involved in chlorophyll biosynthesis and photosynthesis in the dark and repress gene expression by decreasing the acetylation levels and RNA Polymerase II-associated transcription. The binding of HDA15 to the target genes depends on the presence of PIF3. In addition, PIF3 and HDA15 are dissociated from the target genes upon exposure to red light. Taken together, our results indicate that PIF3 associates with HDA15 to repress chlorophyll biosynthetic and photosynthetic genes in etiolated seedlings.

Mixotrophic growth of bacteriochlorophyll a-containing members of the OM60/NOR5 clade of marine gammaproteobacteria is carbon-starvation independent and correlates with the type of carbon source and oxygen availability

BackgroundPopulations of aerobic anoxygenic photoheterotrophic bacteria in marine environments are dominated by members of the Roseobacter lineage within the Alphaproteobacteria and the OM60/NOR5 clade of gammaproteobacteria. A wealth of information exists about the regulation of pigment production and mixotrophic growth in various members of the Roseobacter clade, but a detailed knowledge about aerobic bacteriochlorophyll a-containing gammaproteobacteria is still limited to one strain of the species Congregibacter litoralis.ResultsThe production of photosynthetic pigments and light-dependent mixotrophic growth was analysed in Luminiphilus syltensis DSM 22749T, Chromatocurvus halotolerans DSM 23344T and Pseudohaliea rubra DSM 19751T, representing three taxonomically diverse strains of bacteriochlorophyll a-containing gammaproteobacteria affiliated to the OM60/NOR5 clade. In these strains the expression of a photosynthetic apparatus depended mainly on the type of carbon source and availability of oxygen. The effect of illumination on pigment expression varied significantly between strains. In contrast to Chromatocurvus halotolerans, pigment production in Luminiphilus syltensis and Pseudohaliea rubra was repressed by light of moderate intensities, probably indicating a higher sensitivity to light-induced oxidative stress. The efficiency of using light for mixotrophic growth did not correlate with the cellular level of photosynthetic pigments, but depended mainly on the type of metabolized substrate with malate being the optimal carbon source in most cases.ConclusionsOligotrophic growth conditions or carbon limitation were not required for light-dependent mixotrophic growth in members of the OM60/NOR5 clade. The ability of using light as energy source and the fine tuning of photosynthesis gene expression depended mainly on the type of carbon source and oxygen availability, which indicates that the regulation of pigment production is controlled by the cellular redox state. While light has the main impact on the regulation of photosynthetic pigments in photoheterotrophic representatives of the Roseobacter lineage this was not the case in strains of the OM60/NOR5 clade.

Regulation of bacterial photosynthesis genes by the small noncoding RNA PcrZ

The small RNA PcrZ (photosynthesis control RNA Z) of the facultative phototrophic bacterium Rhodobacter sphaeroides is induced upon a drop of oxygen tension with similar kinetics to those of genes for components of photosynthetic complexes. High expression of PcrZ depends on PrrA, the response regulator of the PrrB/PrrA two-component system with a central role in redox regulation in R. sphaeroides. In addition the FnrL protein, an activator of some photosynthesis genes at low oxygen tension, is involved in redox-dependent expression of this small (s)RNA. Overexpression of full-length PcrZ in R. sphaeroides affects expression of a small subset of genes, most of them with a function in photosynthesis. Some mRNAs from the photosynthetic gene cluster were predicted to be putative PcrZ targets and results from an in vivo reporter system support these predictions. Our data reveal a negative effect of PcrZ on expression of its target mRNAs. Thus, PcrZ counteracts the redox-dependent induction of photosynthesis genes, which is mediated by protein regulators. Because PrrA directly activates photosynthesis genes and at the same time PcrZ, which negatively affects photosynthesis gene expression, this is one of the rare cases of an incoherent feed-forward loop including an sRNA. Our data identified PcrZ as a trans acting sRNA with a direct regulatory function in formation of photosynthetic complexes and provide a model for the control of photosynthesis gene expression by a regulatory network consisting of proteins and a small noncoding RNA.

Effects of the Cryptochrome CryB from Rhodobacter sphaeroides on Global Gene Expression in the Dark or Blue Light or in the Presence of Singlet Oxygen

Several regulators are controlling the formation of the photosynthetic apparatus in the facultatively photosynthetic bacterium Rhodobacter sphaeroides. Among the proteins affecting photosynthesis gene expression is the blue light photoreceptor cryptochrome CryB. This study addresses the effect of CryB on global gene expression. The data reveal that CryB does not only influence photosynthesis gene expression but also genes for the non-photosynthetic energy metabolism like citric acid cycle and oxidative phosphorylation. In addition several genes involved in RNA processing and in transcriptional regulation are affected by a cryB deletion. Although CryB was shown to undergo a photocycle it does not only affect gene expression in response to blue light illumination but also in response to singlet oxygen stress conditions. While there is a large overlap in these responses, some CryB-dependent effects are specific for blue-light or photooxidative stress. In addition to protein-coding genes some genes for sRNAs show CryB-dependent expression. These findings give new insight into the function of bacterial cryptochromes and demonstrate for the first time a function in the oxidative stress response.

Interaction of two photoreceptors in the regulation of bacterial photosynthesis genes

The expression of photosynthesis genes in the facultatively photosynthetic bacterium Rhodobacter sphaeroides is controlled by the oxygen tension and by light quantity. Two photoreceptor proteins, AppA and CryB, have been identified in the past, which are involved in this regulation. AppA senses light by its N-terminal BLUF domain, its C-terminal part binds heme and is redox-responsive. Through its interaction to the transcriptional repressor PpsR the AppA photoreceptor controls expression of photosynthesis genes. The cryptochrome-like protein CryB was shown to affect regulation of photosynthesis genes, but the underlying signal chain remained unknown. Here we show that CryB interacts with the C-terminal domain of AppA and modulates the binding of AppA to the transcriptional repressor PpsR in a light-dependent manner. Consequently, binding of the transcription factor PpsR to its DNA target is affected by CryB. In agreement with this, all genes of the PpsR regulon showed altered expression levels in a CryB deletion strain after blue-light illumination. These results elucidate for the first time how a bacterial cryptochrome affects gene expression.