Regulation Of Photosynthetic Gene Expression Research Articles

Papain-like cysteine proteases are required for the regulation of photosynthetic gene expression and acclimation to high light stress.

Chloroplasts are considered to be devoid of cysteine proteases. Using transgenic Arabidopsis lines expressing the rice cystatin, oryzacystatin I (OC-I), in the chloroplasts (PC lines) or cytosol (CYS lines), we explored the hypothesis that cysteine proteases regulate photosynthesis. The CYS and PC lines flowered later than the wild type (WT) and accumulated more biomass after flowering. In contrast to the PC rosettes, which accumulated more leaf chlorophyll and carotenoid pigments than the WT, the CYS lines had lower amounts of leaf pigments. High-light-dependent decreases in photosynthetic carbon assimilation and the abundance of the Rubisco large subunit protein, the D1 protein, and the phosphorylated form of D1 proteins were attenuated in the CYS lines and reversed in the PC lines relative to the WT. However, the transgenic lines had higher amounts of LHC, rbcs, pasbA, and pasbD transcripts than the WT, and also showed modified chloroplast to nucleus signalling. We conclude that cysteine proteases accelerate the reconfiguration of the chloroplast proteome after flowering and in response to high-light stress. Inhibition of cysteine proteases, such as AtCEP1, slows chloroplast protein degradation and stimulates photosynthetic gene expression and chloroplast to nucleus signalling, enhancing stress tolerance traits.

PTAC10, a Key Subunit of Plastid-Encoded RNA Polymerase, Promotes Chloroplast Development.

Regulation of photosynthetic gene expression by plastid-encoded RNA polymerase (PEP) is essential for chloroplast development. The activity of PEP largely relies on at least 12 PEP-associated proteins (PAPs) encoded in the nuclear genome of plant cells. A recent model proposed that these PAPs regulate the establishment of the PEP complex through broad PAP-PEP or PAP-PAP interactions. In this study, we identified the Arabidopsis (Arabidopsis thaliana) seedling-lethal mutant ptac10-1, which has defects in chloroplast development, and found that the mutant phenotype is caused by the suppression of PLASTID S1 RNA-BINDING DOMAIN PROTEIN (pTAC10/PAP3). Analysis of the heterozygous mutant and pTAC10-overexpressing transgenic plants indicated that the expression level of pTAC10 is tightly linked to chloroplast development. Characterization of the interaction of pTAC10 with PAPs revealed that pTAC10 interacts with other PAPs, such as FSD2, FSD3, TrxZ, pTAC7, and pTAC14, but it does not interact with PEP core enzymes, such as rpoA and rpoB. Analysis of pTAC10 interactions using truncated pTAC10 proteins showed that the pTAC10 carboxyl-terminal region downstream of the S1 domain is involved in the pTAC10-PAP interaction. Furthermore, overexpression of truncated pTAC10s lacking the C-terminal regions downstream of the S1 domain could not rescue the ptac10-1 mutant phenotype and induced an abnormal whitening phenotype in Columbia-0 plants. Our observations suggested that these pTAC10-PAP interactions are essential for the formation of the PEP complex and chloroplast development.

Unique role for translation initiation factor 3 in the light color regulation of photosynthetic gene expression

Light-harvesting antennae are critical for collecting energy from sunlight and providing it to photosynthetic reaction centers. Their abundance and composition are tightly regulated to maintain efficient photosynthesis in changing light conditions. Many cyanobacteria alter their light-harvesting antennae in response to changes in ambient light-color conditions through the process of chromatic acclimation. The control of green light induction (Cgi) pathway is a light-color-sensing system that controls the expression of photosynthetic genes during chromatic acclimation, and while some evidence suggests that it operates via transcription attenuation, the components of this pathway have not been identified. We provide evidence that translation initiation factor 3 (IF3), an essential component of the prokaryotic translation initiation machinery that binds the 30S subunit and blocks premature association with the 50S subunit, is part of the control of green light induction pathway. Light regulation of gene expression has not been previously described for any translation initiation factor. Surprisingly, deletion of the IF3-encoding gene infCa was not lethal in the filamentous cyanobacterium Fremyella diplosiphon, and its genome was found to contain a second, redundant, highly divergent infC gene which, when deleted, had no effect on photosynthetic gene expression. Either gene could complement an Escherichia coli infC mutant and thus both encode bona fide IF3s. Analysis of prokaryotic and eukaryotic genome databases established that multiple infC genes are present in the genomes of diverse groups of bacteria and land plants, most of which do not undergo chromatic acclimation. This suggests that IF3 may have repeatedly evolved important roles in the regulation of gene expression in both prokaryotes and eukaryotes.

Redox regulation of photosynthetic gene expression

Redox chemistry and redox regulation are central to the operation of photosynthesis and respiration. However, the roles of different oxidants and antioxidants in the regulation of photosynthetic or respiratory gene expression remain poorly understood. Leaf transcriptome profiles of a range of Arabidopsis thaliana genotypes that are deficient in either hydrogen peroxide processing enzymes or in low molecular weight antioxidant were therefore compared to determine how different antioxidant systems that process hydrogen peroxide influence transcripts encoding proteins targeted to the chloroplasts or mitochondria. Less than 10 per cent overlap was observed in the transcriptome patterns of leaves that are deficient in either photorespiratory (catalase (cat)2) or chloroplastic (thylakoid ascorbate peroxidase (tapx)) hydrogen peroxide processing. Transcripts encoding photosystem II (PSII) repair cycle components were lower in glutathione-deficient leaves, as were the thylakoid NAD(P)H (nicotinamide adenine dinucleotide (phosphate)) dehydrogenases (NDH) mRNAs. Some thylakoid NDH mRNAs were also less abundant in tAPX-deficient and ascorbate-deficient leaves. Transcripts encoding the external and internal respiratory NDHs were increased by low glutathione and low ascorbate. Regulation of transcripts encoding specific components of the photosynthetic and respiratory electron transport chains by hydrogen peroxide, ascorbate and glutathione may serve to balance non-cyclic and cyclic electron flow pathways in relation to oxidant production and reductant availability.

LIGHT-REGULATED PHOTOSYNTHETIC GENE EXPRESSION AND PHOSPHORIBULOKINASE ENZYME ACTIVITY IN THE HETEROKONT ALGA VAUCHERIA LITOREA (XANTHOPHYCEAE) AND ITS SYMBIOTIC MOLLUSKAN PARTNER ELYSIA CHLOROTICA (GASTROPODA)(1).

Photosynthesis is composed of tightly coupled reactions requiring finely tuned nucleocytosolic-plastid interaction. Herein, we examined the influence of light on select photosynthetic gene expression and enzyme activity in the plastid-containing mollusk (sea slug) Elysia chlorotica and its heterokont algal prey Vaucheria litorea C. Agardh. Transcript levels of nuclear photosynthetic genes (psbO and prk) were significantly lower in E. chlorotica compared with V. litorea, whereas plastid photosynthesis genes (psaA and rbcL) were more comparable, although still lower in the animal. None of the genes responded similarly to changes in light conditions over a 24 h period in the sea slug compared with the alga. Activity of the nuclear-encoded photosynthetic enzyme phosphoribulokinase (PRK) exhibited redox regulation in vitro in crude extracts of both organisms sequentially treated with oxidizing and reducing agents. However, PRK was differentially affected in vivo by redox and light versus dark treatment in V. litorea, but not in E. chlorotica. Overall, these results support the active transcription of algal nuclear and plastid genes in E. chlorotica, as well as sustained activity of a nuclear-encoded plastid enzyme, even after several months of starvation (absence of algal prey). The apparent absence of tight transcriptional regulation and redox control suggests that essential nuclear-encoded regulatory factors in V. litorea are probably not present in the sea slug. These findings are discussed relative to light regulation of photosynthetic gene expression in the green and red algal lineages and in the context of the sea slug/algal plastid kleptoplastic association.

Role of a short light, oxygen, voltage (LOV) domain protein in blue light- and singlet oxygen-dependent gene regulation in Rhodobacter sphaeroides

The facultatively photosynthetic bacterium Rhodobacter sphaeroides harbours an unusual light, oxygen, voltage (LOV) domain protein, RsLOV. While showing a characteristic photocycle, the protein lacks a C-terminal output domain, similar to PpSB2 in Pseudomonas putida. Oxygen tension and light quantity are the two factors mainly responsible for controlling the expression of photosynthesis genes in R. sphaeroides. Two photoreceptor proteins are known to be involved in this regulation: the intensively studied AppA protein and the more recently identified cryptochrome-like protein CryB. Here we show by transcriptome and physiological studies that RsLOV is also involved in the regulation of photosynthetic gene expression. Our data further hint at a connection between RsLOV, carbohydrate metabolism and chemotaxis, as well as with the cellular response to photooxidative stress. RsLOV affects not only blue light-dependent gene expression but also redox-dependent regulation.

Blue Light-responsive Regulation of Photosynthetic Gene Expression

Blue Light-responsive Regulation of Photosynthetic Gene Expression

Regulation of photosynthetic gene expression in purple bacteria.

Purple phototrophic bacteria have the ability to capture and use sunlight efficiently as an energy source. In these organisms, photosynthesis is carried out under anaerobic conditions. The introduction of oxygen into a culture growing phototrophically results in a rapid decrease in the synthesis of components of the photosynthetic apparatus and a change to an alternative source of energy, usually derived from the degradation of organic compounds under aerobic conditions (chemoheterotrophy). Switching back and forth between anaerobic (photosynthetic) and aerobic growth requires tight regulation of photosynthetic gene expression at the molecular level. Initial experiments by Cohen-Bazire et al. (1957) showed quite clearly that the regulation of photosynthetic gene expression was in response to two environmental stimuli. The most potent stimulus was oxygen; its presence shut down production of photosynthetic pigments very rapidly. To a lesser extent photosynthetic gene expression responded to light intensity. Low light intensity produced high levels of photosynthetic pigments; high light intensities caused a decrease, but the effect was less dramatic than that observed for oxygen. Since these initial observations were made in Rhodobacter sphaeroides some forty years ago, a great deal has been revealed as to the nature of the genes that encode the various components of the photosynthetic apparatus. Recent progress in the understanding of the regulation of expression of these genes in R. sphaeroides and Rhodobacter capsulatus is the subject of this review.

Nitrogen-dependent regulation of photosynthetic gene expression

Nitrogen-limited Chlamydomonas reinhardtii is chlorotic and very deficient in chlorophyll a/b light-harvesting complexes (LHC). Rates of synthesis of photosynthetic proteins, but especially the LHC apoproteins, are reduced 10- to 40-fold. Moderately high levels of chloroplast transcripts accumulate in nitrogen-limited cells, and there is a correlation between chloroplast DNA levels and chloroplast mRNA abundance. In contrast, nuclear transcripts encoding LHCII and ribulose 1,5-bisphosphate carboxylase small subunits are markedly reduced. Thus, nitrogen availability affects chloroplast protein synthesis by inhibition of translation and, to a lesser extent, chloroplast DNA amplification. Regulation of nuclear-encoded photosynthetic proteins by nitrogen is achieved through mechanisms affecting transcription and/or mRNA stability.