Regulation Of Photosynthesis Research Articles

Transcriptomic and Metabolomic Analyses Reveal the Importance of Lipid Metabolism and Photosynthesis Regulation in High Salinity Tolerance in Barley (Hordeum vulgare L.) Leaves Derived from Mutagenesis Combined with Microspore Culture

Barley is the most salt-tolerant cereal crop. However, little attention has been paid to the salt-tolerant doubled haploids of barley derived from mutagenesis combined with isolated microspore culture. In the present study, barley doubled haploid (DH) line 20, which was produced by mutagenesis combined with isolated microspore culture, showed stably and heritably better salt tolerance than the wild type H30 in terms of fresh shoot weight, dry shoot weight, K+/Na+ ratio and photosynthetic characteristics. Transcriptome and metabolome analyses were performed to compare the changes in gene expression and metabolites between DH20 and H30. A total of 462 differentially expressed genes (DEGs) and 152 differentially accumulated metabolites (DAMs) were identified in DH20 compared to H30 under salt stress. Among the DAMs, fatty acids were the most accumulated in DH20 under salt stress. The integration of transcriptome and metabolome analyses revealed that nine key biomarkers, including two metabolites and seven genes, could distinguish DH20 and H30 when exposed to high salt. The pathways of linoleic acid metabolism, alpha-linolenic acid metabolism, glycerolipid metabolism, photosynthesis, and alanine, aspartate and glutamate metabolism were significantly enriched in DH20 with DEGs and DAMs in response to salt stress. These results suggest that DH20 may enhance resilience by promoting lipid metabolism, maintaining energy metabolism and decreasing amino acids metabolism. The study provided novel insights for the rapid generation of homozygous mutant plants by mutagenesis combined with microspore culture technology and also identified candidate genes and metabolites that may enable the mutant plants to cope with salt stress.

Engineering photo-methylotrophic Methylobacterium for enhanced 3-hydroxypropionic acid production during non-growth stage fermentation

This study explored the potential of methanol as a sustainable feedstock for biomanufacturing, focusing on Methylobacterium extorquens, a well-established representative of methylotrophic cell factories. Despite this bacterium’s long history, its untapped photosynthetic capabilities for production enhancement have remained unreported. Using genome-scale flux balance analysis, it was hypothesized that introducing photon fluxes could boost the yield of 3-hydroxypropionic acid (3-HP), an energy- and reducing equivalent-consuming chemicals. To realize this, M. extorquens was genetically modified by eliminating the negative regulator of photosynthesis, leading to improved ATP levels and metabolic activity in non-growth cells during a two-stage fermentation process. This modification resulted in a remarkable 3.0-fold increase in 3-HP titer and a 2.1-fold increase in its yield during stage (II). Transcriptomics revealed that enhanced light-driven methanol oxidation, NADH transhydrogenation, ATP generation, and fatty acid degradation were key factors. This development of photo-methylotrophy as a platform technology introduced novel opportunities for future production enhancements.

Light quality regulates plant biomass and fruit quality through a photoreceptor-dependent HY5-LHC/CYCB module in tomato

Abstract Increasing photosynthesis and light capture offers possibilities for improving crop yield and provides a sustainable way to meet the increasing global demand for food. However, the poor light transmittance of transparent plastic films and shade avoidance at high planting density seriously reduce photosynthesis and alter fruit quality in vegetable crops, and therefore it is important to investigate the mechanisms of light signaling regulation of photosynthesis and metabolism in tomato (Solanum lycopersicum). Here, a combination of red, blue, and white (R1W1B0.5) light promoted the accumulation of chlorophyll, carotenoid, and anthocyanin, and enhanced photosynthesis and electron transport rates by increasing the density of active reaction centers and the expression of the genes LIGHT-HARVESTING COMPLEX B (SlLHCB) and A (SlLHCA), resulting in increased plant biomass. In addition, R1W1B0.5 light induced carotenoid accumulation and fruit ripening by decreasing the expression of LYCOPENE β-CYCLASE (SlCYCB). Disruption of SlCYCB largely induced fruit lycopene accumulation, and reduced chlorophyll content and photosynthesis in leaves under red, blue, and white light. Molecular studies showed that ELONGATED HYPOCOTYL 5 (SlHY5) directly activated SlCYCB, SlLHCB, and SlLHCA expression to enhance chlorophyll accumulation and photosynthesis. Furthermore, R1W1B0.5 light-induced chlorophyll accumulation, photosynthesis, and SlHY5 expression were largely decreased in the slphyb1cry1 mutant. Collectively, R1W1B0.5 light noticeably promoted photosynthesis, biomass, and fruit quality through the photoreceptor (SlPHYB1 and SlCRY1)-SlHY5-SlLHCA/B/SlCYCB module in tomato. Thus, the manipulation of light environments in protected agriculture is a crucial tool to regulate the two vital agronomic traits related to crop production efficiency and fruit nutritional quality in tomato.

Regulation of photosynthesis and water-use efficiency in pima and upland cotton species subjected to drought and recovery

Regulation of photosynthesis and water-use efficiency in pima and upland cotton species subjected to drought and recovery

COBL7 is required for stomatal formation via regulation of cellulose deposition in Arabidopsis.

As a key regulator of plant photosynthesis, water use efficiency and immunity, stomata are specialized cellular structures that adopt defined shapes. However, our knowledge about the genetic players of stomatal pore formation and stomatal morphogenesis remains limited. Forward genetic screening, positional cloning, confocal and electron microscopy, physiological and pharmacological assays were employed for isolation and characterization of mutants and genes. We identified a mutant, dsm1, with impaired cytokinesis and deformed stomata. DSM1 is highly expressed in guard mother cells and guard cells, and encodes COBRA-LIKE 7 (COBL7), a plant-specific glycosylphosphatidylinositol (GPI)-anchored protein. COBRA-LIKE 7 and its closest homologue, COBL8, are first enriched on the forming cell plates during cytokinesis, and then their subcellular distribution and abundance change are correlated with the progressive stages of stomatal pore formation. Both COBL7 and COBL8 possess an ability to bind cellulose. Perturbing the expression of COBL7 and COBL8 leads to a decrease in cellulose content and inhibition of stomatal pore development. Moreover, we found that COBL7, COBL8 and CSLD5 have synergistic effects on stomatal development and plant growth. Our findings reveal that COBL7 plays a predominant and functionally redundant role with COBL8 in stomatal formation through regulating cellulose deposition and ventral wall modification in Arabidopsis.

Photosynthesis regulation, cell membrane stabilization and methylglyoxal detoxification seems major altered pathways under cold stress as revealed by integrated multi-omics meta-analysis.

The online version contains supplementary material available at 10.1007/s12298-023-01367-9.

Ultra-Fast Mass Spectrometry in Plant Biochemistry: Response of Winter Wheat Proteomics to Pre-Sowing Treatment with Iron Compounds.

In recent years, ultrafast liquid chromatography/mass spectrometry methods have been extensively developed for the use in proteome profiling in biochemical studies. These methods are intended for express monitoring of cell response to biotic stimuli and elucidation of correlation of molecular changes with biological processes and phenotypical changes. New technologies, including the use of nanomaterials, are actively introduced to increase agricultural production. However, this requires complex approbation of new fertilizers and investigation of mechanisms underlying the biotic effects on the germination, growth, and development of plants. The aim of this work was to adapt the method of ultrafast chromatography/mass spectrometry for rapid quantitative profiling of molecular changes in 7-day-old wheat seedlings in response to pre-sowing seed treatment with iron compounds. The used method allows to analyze up to 200 samples per day; its practical value lies in the possibility of express proteomic diagnostics of the biotic action of new treatments, including those intended for agricultural needs. Changes in the regulation of photosynthesis, biosynthesis of chlorophyll and porphyrin- and tetrapyrrole-containing compounds, glycolysis (in shoot tissues), and polysaccharide metabolism (in root tissues) were shown after seed treatment with suspensions containing film-forming polymers (PEG 400, Na-CMC, Na2-EDTA), iron (II, III) nanoparticles, or iron (II) sulfate. Observations at the protein levels were consistent with the results of morphometry, superoxide dismutase activity assay, and microelement analysis of 3-day-old germinated seeds and shoots and roots of 7-day-old seedlings. A characteristic molecular signature involving proteins participating in the regulation of photosynthesis and glycolytic process was suggested as a potential marker of the biotic effects of seed treatment with iron compounds, which will be confirmed in further studies.

Regulation of photosynthesis by mitogen-activated protein kinase in rice: antagonistic adjustment by OsMPK3 and OsMPK6.

The online version contains supplementary material available at 10.1007/s12298-023-01383-9.

Effects of hydrogen sulfide on the growth and physiological characteristics of Miscanthus sacchariflorus seedlings under cadmium stress

As a gas signal molecule, hydrogen sulfide (H2S) can participate in many physiological and biochemical processes such as seed germination and photosynthesis regulation. In order to explore the regulatory effect of H2S on the growth of Miscanthus sacchariflorus under Cd stress and to provide sufficient theoretical basis for the complex action of H2S and energy plants to remediate soil pollution. In this experiment, the effects of different concentrations of H2S (10, 25, 50, 100, 300, 400, 500 μmol·L−1 (μM)) pretreatment on the growth index, lipid peroxidation degree, chlorophyll (Chl) content, osmoregulation substance content, antioxidant enzyme activity and non-enzymatic antioxidant content of M. sacchariflorus under Cd stress (50 μM) were studied. The results showed that under Cd stress, the reactive oxygen species (ROS) content in the body of M. sacchariflorus was unbalanced, and the growth were severely inhibited, the activities of antioxidant enzymes, such as catalase (CAT) and superoxide dismutase (SOD) significantly decreased, and the content of osmoregulation substance, ascorbic acid (AsA) and glutathione (GSH) significantly increased. With the increase of H2S concentration, its effect on resisting Cd stress can be shown as "low concentration promotes, high concentration inhibits". When the concentration of H2S ≤ 300 μM, although there was no significant difference in Cd content compared with Cd treatment alone, it can regulate the activities of peroxidase (POD), SOD, glutathione reductase (GR) and monodehydroascorbate reductase (MDHAR), increase the content of osmoregulation substances, oxidized glutathione (GSSG), and the transformation rate of AsA and dehydroascorbic acid (DHA) to reduce the oxidative damage and improve the growth and photosynthetic indicators of plants; when the concentration of H2S ≥ 400 μM, Cd content in the ground and root decreased significantly, but the transport factor increased significantly, the growth status of M. sacchariflorus were more severely inhibited by the combined stress of H2S and Cd. In this experiment, it was found that the concentration of H2S pretreatment ≤ 300 μM could regulate the growth of M. sacchariflorus under Cd stress to normal level, and when the treatment concentration was 50 μM, the effect was the best. It will provide a new idea for the treatment of contaminated soil by energy plants.

Glycolate oxidase gene family identification and functional analyses in cotton resistance to Verticillium wilt.

Glycolate oxidase (GOX) plays an important role in the regulation of photorespiration and photosynthesis in plants. However, as one of the main enzymes to produce the second messenger hydrogen peroxide (H2O2), its functions in response to pathogens are still poorly understood. In this study, we carried out genome-wide identification, and 14 GOX genes were identified in Gossypium hirsutum. These GOX genes are located on 10 chromosomes and divided into hydroxyacid-oxidases (HAOX) and GOX groups. After infection with Verticillium dahliae Kleb., six GOX gene expression levels were changed. Moreover, H2O2, salicylic acid (SA), and the content and activity of GOX increased in cotton. GhHAOX2-D-silenced plants showed more wilting than control plants after infection with V. dahliae. Additionally, H2O2 accumulation and SA content were reduced in GhHAOX2-D-silenced plants. The expression levels of GhPAL, GhPAD4, and GhPR1 and the lignin content of the silenced plants were significantly lower than those of the control plants. These results indicate that GhHAOX2-D is a positive regulator of Verticillium wilt tolerance in cotton and may promote H2O2 accumulation via the synergistic effects of GOX genes and SA. Collectively, GOX genes play an important role in cotton resistance to Verticillium wilt.

Genome-wide mapping of DNase I hypersensitive sites in pineapple leaves.

Pineapple [Ananas comosus (L.) Merr.] is the most economically important crop possessing crassulacean acid metabolism (CAM) photosynthesis which has a higher water use efficiency by control of nocturnal opening and diurnal closure of stomata. To provide novel insights into the diel regulatory landscape in pineapple leaves, we performed genome-wide mapping of DNase I hypersensitive sites (DHSs) in pineapple leaves at day (2a.m.) and night (10a.m.) using a simplified DNase-seq method. As a result, totally 33340 and 28753 DHSs were found in green-tip tissue, and 29597 and 40068 were identified in white-base tissue at 2a.m. and 10a.m., respectively. We observed that majority of the pineapple genes occupied less than two DHSs with length shorter than 1kb, and the promotor DHSs showed a proximal trend to the transcription start site (>77% promotor DHSs within 1kb). In addition, more intergenic DHSs were identified around transcription factors or transcription co-regulators (TFs/TCs) than other functional genes, indicating complex regulatory contexts around TFs/TCs. Through combined analysis of tissue preferential DHSs and genes, we respectively found 839 and 888 coordinately changed genes in green-tip at 2a.m. and 10a.m. (AcG2 and AcG10). Furthermore, AcG2-specific, AcG10-specific and common accessible DHSs were dissected from the total photosynthetic preferential DHSs, and the regulatory networks indicated dynamic regulations with multiple cis-regulatory elements occurred to genes preferentially expressed in photosynthetic tissues. Interestingly, binding motifs of several cycling TFs were identified in the DHSs of key CAM genes, revealing a circadian regulation to CAM coordinately diurnal expression. Our results provide a chromatin regulatory landscape in pineapple leaves during the day and night. This will provide important information to assist with deciphering the circadian regulation of CAM photosynthesis.

SlTDC1 Overexpression Promoted Photosynthesis in Tomato under Chilling Stress by Improving CO2 Assimilation and Alleviating Photoinhibition

Chilling causes a significant decline in photosynthesis in tomato plants. Tomato tryptophan decarboxylase gene 1 (SlTDC1) is the first rate-limiting gene for melatonin (MT) biosynthesis and is involved in the regulation of photosynthesis under various abiotic stresses. However, it is not clear whether SlTDC1 participates in the photosynthesis of tomato under chilling stress. Here, we obtained SlTDC1 overexpression transgenic tomato seedlings, which showed higher SlTDC1 mRNA abundance and MT content compared with the wild type (WT). The results showed that the overexpression of SlTDC1 obviously alleviated the chilling damage to seedlings in terms of the lower electrolyte leakage rate and hydrogen peroxide content, compared with the WT after 2 d of chilling stress. Moreover, the overexpression of SlTDC1 notably increased photosynthesis under chilling stress, which was related to the higher chlorophyll content, normal chloroplast structure, and higher mRNA abundance and protein level of Rubisco and RCA, as well as the higher carbon metabolic capacity, compared to the WT. In addition, we found that SlTDC1-overexpressing seedlings showed higher Wk (damage degree of OEC on the PSII donor side), φEo (quantum yield for electron transport in the PSII reaction center), and PIABS (photosynthetic performance index) than WT seedlings after low-temperature stress, implying that the overexpression of SlTDC1 decreased the damage to the reaction center and donor-side and receptor-side electron transport of PSII and promoted PSI activity, as well as energy absorption and distribution, to relieve the photoinhibition induced by chilling stress. Our results support the notion that SlTDC1 plays a vital role in the regulation of photosynthesis under chilling stress.

The cytochrome b6f complex: plastoquinol oxidation and regulation of electron transport in chloroplasts.

In oxygenic photosynthetic systems, the cytochrome b6f (Cytb6f) complex (plastoquinol:plastocyanin oxidoreductase) is a heart of the hub that provides connectivity between photosystems (PS) II and I. In this review, the structure and function of the Cytb6f complex are briefly outlined, being focused on the mechanisms of a bifurcated (two-electron) oxidation of plastoquinol (PQH2). In plant chloroplasts, under a wide range of experimental conditions (pH and temperature), a diffusion of PQH2 from PSII to the Cytb6f does not limit the intersystem electron transport. The overall rate of PQH2 turnover is determined mainly by the first step of the bifurcated oxidation of PQH2 at the catalytic site Qo, i.e., the reaction of electron transfer from PQH2 to the Fe2S2 cluster of the high-potential Rieske iron-sulfur protein (ISP). This point has been supported by the quantum chemical analysis of PQH2 oxidation within the framework of a model system including the Fe2S2 cluster of the ISP and surrounding amino acids, the low-potential heme b6L, Glu78 and 2,3,5-trimethylbenzoquinol (the tail-less analog of PQH2). Other structure-function relationships and mechanisms of electron transport regulation of oxygenic photosynthesis associated with the Cytb6f complex are briefly outlined: pH-dependent control of the intersystem electron transport and the regulatory balance between the operation of linear and cyclic electron transfer chains.

Studying the effect of light intensity on the photosynthetic mechanism of pepper leaf yellowing mutants by proteomics and phosphoproteomics

The leaf is an important plant organ and is closely related to agricultural yield. Photosynthesis plays a critical role in promoting plant growth and development. Understanding the mechanism of leaf photosynthesis regulation will help improve crop yield. In this study, the pepper yellowing mutant was used as the experimental material, and the photosynthetic changes of pepper leaves (yl1 and 6421) under different light intensities were analyzed by chlorophyll fluorimeter and photosynthesis meter. Changes in proteins and enrichment of phosphopeptides in pepper leaves were determined. The results showed that different light intensities had significant effects on the chlorophyll fluorescence and photosynthetic parameters of pepper leaves. The differentially expressed proteins (DEPs) and differentially expressed phosphorylated proteins (DEPPs) were mainly involved in photosynthesis, photosynthesis-antenna proteins, and carbon fixation in photosynthetic organisms. In yl1 leaves, the phosphorylation levels of photosynthesis and photosynthesis-antenna proteins LHCA2, LHCA3, PsbC, PsbO, and PsbP were lower under low light treatment, but significantly higher under high light intensity compared with wild-type leaves. In addition, many proteins involved in the carbon assimilation pathway, including TKT, Rubisco, and PGK, were phosphorylated, and this modification level was significantly higher in yl1 than in the wild type under high light intensity. These results provide a new perspective for studying the photosynthesis mechanism of pepper under different light intensities.

Modulation of xanthophyll cycle impacts biomass productivity in the marine microalga Nannochloropsis

Life on earth depends on photosynthetic primary producers that exploit sunlight to fix CO2 into biomass. Approximately half of global primary production is associated with microalgae living in aquatic environments. Microalgae also represent a promising source of biomass to complement crop cultivation, and they could contribute to the development of a more sustainable bioeconomy. Photosynthetic organisms evolved multiple mechanisms involved in the regulation of photosynthesis to respond to highly variable environmental conditions. While essential to avoid photodamage, regulation of photosynthesis results in dissipation of absorbed light energy, generating a complex trade-off between protection from stress and light-use efficiency. This work investigates the impact of the xanthophyll cycle, the light-induced reversible conversion of violaxanthin into zeaxanthin, on the protection from excess light and on biomass productivity in the marine microalgae of the genus Nannochloropsis. Zeaxanthin is shown to have an essential role in protection from excess light, contributing to the induction of nonphotochemical quenching and scavenging of reactive oxygen species. On the contrary, the overexpression of zeaxanthin epoxidase enables a faster reconversion of zeaxanthin to violaxanthin that is shown to be advantageous for biomass productivity in dense cultures in photobioreactors. These results demonstrate that zeaxanthin accumulation is critical to respond to strong illumination, but it may lead to unnecessary energy losses in light-limiting conditions and accelerating its reconversion to violaxanthin provides an advantage for biomass productivity in microalgae.

Plant NADPH-dependent thioredoxin reductases are crucial for the metabolism of sink leaves and plant acclimation to elevated CO2.

Plants contain three NADPH-thioredoxin reductases (NTR) located in the cytosol/mitochondria (NTRA/B) and the plastid (NTRC) with important metabolic functions. However, mutants deficient in all NTRs remained to be investigated. Here, we generated and characterised the triple Arabidopsis ntrabc mutant alongside with ntrc single and ntrab double mutants under different environmental conditions. Both ntrc and ntrabc mutants showed reduced growth and substantial metabolic alterations, especially in sink leaves and under high CO2 (HC), as compared to the wild type. However, ntrabc showed higher effective quantum yield of PSII under both constant and fluctuating light conditions, altered redox states of NADH/NAD+ and glutathione (GSH/GSSG) and lower potential quantum yield of PSII in sink leaves in ambient but not high CO2 concentrations, as compared to ntrc, suggesting a functional interaction between chloroplastic and extra-chloroplastic NTRs in photosynthesis regulation depending on leaf development and environmental conditions. Our results unveil a previously unknown role of the NTR system in regulating sink leaf metabolism and plant acclimation to HC, while it is not affecting full plant development, indicating that the lack of the NTR system can be compensated, at least to some extent, by other redox mechanisms.

Long-term light adaptation of light-harvesting and energy-transfer processes in the glaucophyte Cyanophora paradoxa under different light conditions.

In response to fluctuation in light intensity and quality, oxygenic photosynthetic organisms modify their light-harvesting and excitation energy-transfer processes to maintain optimal photosynthetic activity. Glaucophytes, which are a group of primary symbiotic algae, possess light-harvesting antennas called phycobilisomes (PBSs) consistent with cyanobacteria and red algae. However, compared with cyanobacteria and red algae, glaucophytes are poorly studied and there are few reports on the regulation of photosynthesis in the group. In this study, we examined the long-term light adaptation of light-harvesting functions in a glaucophyte, Cyanophora paradoxa, grown under different light conditions. Compared with cells grown under white light, the relative number of PBSs to photosystems (PSs) increased in blue-light-grown cells and decreased in green-, yellow-, and red-light-grown cells. Moreover, the PBS number increased with increment in the monochromatic light intensity. More energy was transferred from PBSs to PSII than to PSI under blue light, whereas energy transfer from PBSs to PSII was reduced under green and yellow lights, and energy transfer from the PBSs to both PSs decreased under red light. Decoupling of PBSs was induced by intense green, yellow, and red lights. Energy transfer from PSII to PSI (spillover) was observed, but the contribution of the spillover did not distinctly change depending on the culture light intensity and quality. These results suggest that the glaucophyte C. paradoxa modifies the light-harvesting abilities of both PSs and excitation energy-transfer processes between the light-harvesting antennas and both PSs during long-term light adaption.

Erodium oxyrhinchum sustains severe drought stress by maintaining stable photosynthetic electron transport under progressive drought conditions

Drought is a key environmental factor limiting the growth and development of desert plants. In this experiment, we investigated the response of photosynthesis in the ephemeral plant E. oxyrhinchum to progressive drought conditions in its natural habitat. In response to drought stress, the mechanism for photosynthesis regulation in E. oxyrhinchum is switched from stomatal to non-stomatal limitations. One notable characteristic of E. oxyrhinchum is its ability to sustain photosynthesis under severe drought conditions. This is because the transition from stomatal to non-stomatal limitation occurred at a much lower leaf water content (56.51% ± 8.53%), compared to that in other plant species. With the drought treatment, the net photosynthetic rate was maintained or even increased to a much higher value to that of the control (33.65 ± 1.72 vs. 17.65 ± 2.35 μmol CO2 m-2s-1), which coincided with the increased stomatal conductance. During the entire stomatal limitation to the photosynthesis stage, the maximum photochemical efficiency of photosystem II (Fv/Fm) remained unchanged. Additionally, the prompt Chl a fluorescence induction was stable, which indicated an intact photosystem II structure and a balanced redox state of the plastoquinone pool. The variation partition analysis revealed that the substantial increase in antioxidant activities and sensitive response to nonphotochemical quenching during this stage contributed significantly to maintaining a stable Fv/Fm value. To conclude, we have not only provided novel information regarding the drought-escape E. oxyrhinchum species but also concluded that PSII activity modulates the switch from stomatal to non-stomatal photosynthesis limitation under progressive drought conditions.

CsXDH1 gene promotes caffeine catabolism induced by continuous strong light in tea plant.

Tea plant (Camellia sinensis) is an important cash crop with extensive adaptability in the world. However, complex environmental factors force a large variation of tea quality-related components. Caffeine is essential for the formation of bitter and fresh flavors in tea, and is the main compound of tea that improves human alertness. Continuous strong light stimulation was observed to cause caffeine reduction in tea leaves, but the mechanism is not clear. In this study, the response of tea plant to light intensity was analysed mainly by multi-omics association, antisense oligodeoxynucleotide (asODN) silencing technique, and in vitro enzyme activity assay. The results revealed multiple strategies for light intensity adaptation in tea plant, among which the regulation of chloroplasts, photosynthesis, porphyrin metabolism, and resistance to oxidative stress were prominent. Caffeine catabolism was enhanced in continuous strong light, which may be a light-adapted strategy due to strict regulation by xanthine dehydrogenase (XDH). asODN silencing and enzymatic activity assays confirmed that CsXDH1 is a protein induced by light intensity to catalyze the substrate xanthine. CsXDH1 asODN silencing resulted in significant up-regulation of both caffeine and theobromine in in vitro enzyme activity assay, but not in vivo. CsXDH1 may act as a coordinator in light intensity adaptation, thus disrupting this balance of caffeine catabolism.

Low light intensity elongates period and defers peak time of photosynthesis: a computational approach to circadian-clock-controlled photosynthesis in tomato.

Photosynthesis is involved in the essential process of transforming light energy into chemical energy. Although the interaction between photosynthesis and the circadian clock has been confirmed, the mechanism of how light intensity affects photosynthesis through the circadian clock remains unclear. Here, we propose a first computational model for circadian-clock-controlled photosynthesis, which consists of the light-sensitive protein P, the core oscillator, photosynthetic genes, and parameters involved in the process of photosynthesis. The model parameters were determined by minimizing the cost function ( [Formula: see text]), which is defined by the errors of expression levels, periods, and phases of the clock genes (CCA1, PRR9, TOC1, ELF4, GI, and RVE8). The model recapitulates the expression pattern of the core oscillator under moderate light intensity (100μmolm -2s-1). Further simulation validated the dynamic behaviors of the circadian clock and photosynthetic outputs under low (62.5μmolm-2s-1) and normal (187.5μmolm-2s-1) intensities. When exposed to low light intensity, the peak times of clock and photosynthetic genes were shifted backward by 1-2hours, the period was elongated by approximately the same length, and the photosynthetic parameters attained low values and showed delayed peak times, which confirmed our model predictions. Our study reveals a potential mechanism underlying the circadian regulation of photosynthesis by the clock under different light intensities in tomato.