Carbon Reallocation Research Articles

Multi-omics analyses reveal mechanism for high resistant starch formation in an indica rice SSIIIa mutant

Soluble starch synthase IIIa (SSIIIa) is a key enzyme involved in amylopectin biosynthesis in rice, and deficiency of SSIIIa results in high content of resistant starch, which is benefit to human health. However, little is known about metabolic differences and carbon re-allocation in the seeds of the indica rice ss3a mutant. We found that SSIIIa deficiency impaired the storage of starch, but increased the soluble sugars, free amino acids and lipids. By multi-omic analyses, we found inactivation of SSIIIa triggered carbon repartitioning by downregulating sucrose synthase, grain incomplete filling 1, fructokinase and hexokinase (HK), and promoted the accumulation of soluble sugars. Meanwhile, the downregulation of HK and upregulation of plastidic phosphoglucomutase reduced the carbon flow through glycolysis and promoted glycogenesis. The downregulation of OsbZIP58 and the deleterious effect on ribosome formation might result in the reduction of storage protein synthesis and increased free amino acids content in ss3a. The higher levels of amylose and lipids could form more amylose-lipid complexes (starch phospholipids), resulting in a higher resistant starch content. Taken together, our study unraveled a functional cross talk between starch, protein and lipids in rice endosperm during seed development of ss3a, providing new insights for formation of high resistant starch in rice.

Comparative proteomics analysis of root and nodule mitochondria of soybean.

Legumes perform symbiotic nitrogen fixation through rhizobial bacteroids housed in specialised root nodules. The biochemical process is energy-intensive and consumes a huge carbon source to generate sufficient reducing power. To maintain the symbiosis, malate is supplied by legume nodules to bacteroids as their major carbon and energy source in return for ammonium ions and nitrogenous compounds. To sustain the carbon supply to bacteroids, nodule cells undergo drastic reorganisation of carbon metabolism. Here, a comprehensive quantitative comparison of the mitochondrial proteomes between root nodules and uninoculated roots was performed using data-independent acquisition proteomics, revealing the modulations in nodule mitochondrial proteins and pathways in response to carbon reallocation. Corroborated our findings with that from the literature, we believe nodules preferably allocate cytosolic phosphoenolpyruvates towards malate synthesis in lieu of pyruvate synthesis, and nodule mitochondria prefer malate over pyruvate as the primary source of NADH for ATP production. Moreover, the differential regulation of respiratory chain-associated proteins suggests that nodule mitochondria could enhance the efficiencies of complexes I and IV for ATP synthesis. This study highlighted a quantitative proteomic view of the mitochondrial adaptation in soybean nodules.

Day–night discrepancy in soil respiration varies with seasons in a temperate forest

Abstract Soil respiration (Rs) during daytime (Rsday) and nighttime (Rsnight) remains poorly understood owing to the limited availability of high‐resolution temporal measurements of Rs. Using continuous automatic chamber measurements at a half‐hourly interval, we explored Rs and its temperature sensitivity (Q10) during the daytime and nighttime over 10 years and determined the best sampling timeslot in a temperate deciduous broadleaf forest. We demonstrate a higher Rsnight than Rsday in spring and summer, a lower Rsnight than Rsday in autumn, but an insignificant difference between them in winter, contrasting with the consensus of a higher Rsday than Rsnight. Such discrepancy may result from the effect of factors other than temperature (e.g. reallocation of photosynthesis carbon, precipitation and soil moisture). We also reveal significant differences in apparent Q10 between seasons, indicating the highest Q10 in spring and significantly higher Q10 at night than at day in autumn. The Rs measured around midday (9:00–11:00 for autumn and 12:00–15:00 for other seasons) and midnight (20:00–22:00 for autumn and 0:00–2:00 for other seasons) provides the lowest bias to the daily mean Rs, whereas the measurement timeslots around midday are preferred due to practical considerations. Our findings highlight the significant diel variation of Rs and its temperature sensitivity across seasons and the necessity to account for Rsnight for a more accurate estimate of soil carbon budget. Read the free Plain Language Summary for this article on the Journal blog.

Changing climate sensitivity of secondary growth following extreme drought events in forest ecosystems: a global analysis

Understanding tree-response to extreme drought events is imperative for maintaining forest ecosystem services under climate change. While tree-ring derived secondary growth measurements are often used to estimate direct and lagging drought impacts, so-called drought legacies, underlying physiological responses remain difficult to constrain across species and site conditions. As extreme droughts may alter the functioning of plants in terms of resource allocation being shifted towards repair and physiological adjustments, climate control on growth may consequently be altered until physiological recovery is completed. In this context, we here advance the concept of drought legacy effects by quantifying ‘functional legacies’ as climate sensitivity deviations (CSD) of secondary growth after droughts, i.e. temporary alterations of climate-growth relations. We quantified climate sensitivity deviations after extreme drought events by applying linear mixed-effects models to a global-scale, multi-species tree-ring dataset and differentiated responses by clades, site aridity and hydraulic safety margins (HSMs). We found that while direct secondary growth legacies were common across these groups, responses in post-drought climate sensitivity deviations were nuanced. Gymnosperms showed weaker coupling between secondary growth and the dominant climatic driver after droughts, a response that was narrowed down to gymnosperms with a small HSM, i.e. risky hydraulic strategy. In comparison, angiosperms instead showed stronger coupling between secondary growth and the dominant climatic driver following droughts, which was narrowed down to the angiosperms growing in arid sites. These results are consistent with current understanding of physiological impairment and carbon reallocation mechanisms, and the distinct functional responses suggest functional legacies quantified by climate sensitivity deviations is a promising avenue for detecting and thus studying physiological mechanisms underlying drought-responses in tree growth on large scales.

Drip irrigation improves spring wheat water productivity by reducing leaf area while increasing yield

To mitigate the climate change-induced water shortage and realize the sustainable development of agriculture, drip irrigation, a more efficient water-saving irrigation method, has been intensively implemented in most arid agricultural regions in the world. However, compared to traditional border irrigation, how drip irrigation affects the biophysical conditions in the cropland and how crops physiologically respond to changes in biophysical conditions in terms of water, heat and carbon exchange remain largely unknown. In view of the above situation, to reveal the mechanism of drip irrigation in improving spring wheat water productivity, paired field experiments based on drip irrigation and border irrigation were conducted to extensively monitor water and heat fluxes at a typical spring wheat field (Triticum aestivum L.) in Northwest China during 2017–2020. The results showed that drip irrigation improved yield by 10.3 % and crop water productivity (i.e., yield-to-evapotranspiration-ratio) by 15.6 %, but reduced LAI by 16.9 % in contrast with border irrigation. Under drip irrigation, the lateral development of spring wheat roots was promoted by higher soil temperature combined with frequent dry-wet alternation in the shallow soil layer (0–20 cm), which was the basis for efficient absorption of water and fertilizer, as well as efficient formation of photosynthate. Meanwhile, drip irrigation increased net radiation and decreased latent heat flux by inhibiting leaf growth, thereby increased sensible heat, causing a higher soil temperature (+1.10 ℃) and canopy temperature (+1.11 ℃). Further analysis proved that soil temperature was the key factor affecting yield formation. Based on the above conditions, the decrease in leaf distribution coefficient (−0.030) led to the decrease in evapotranspiration (−5.7 %) and the increase in ear distribution coefficient (+0.029). Therefore, drip irrigation emphasized the role of soil moisture in the soil-plant-atmosphere continuum, enhanced crop activity by increasing field temperature, especially soil temperature, and finally improved yield and water productivity via carbon reallocation. The study revealed the mechanism of drip irrigation for improving spring wheat yield, and would contribute to improving Earth system models in representing agricultural cropland ecosystems with drip irrigation and predicting the subsequent biophysical and biogeochemical feedbacks to climate change.

Species Richness Promotes Productivity through Tree Crown Spatial Complementarity in a Species-Rich Natural Forest

Ecological theory suggests that species with complementary architectural and physiological traits can optimize crown packing to improve resource efficiency and promote ecosystem productivity in forest communities. However, empirical evidence of this prediction is rare in species-rich natural forests, as little is known about how crown spatial complementarity regulates community species richness-productivity relationship (SRPR). In this study, we measured tree architectural traits (stem diameter, height, crown depth and width) for 11,337 trees, and quantified species richness, functional diversity, crown spatial complementarity, soil fertility and forest productivity for 44 quadrats (20 m × 20 m per quadrat) in the Badagongshan 25 ha forest plot, central China. We tested bivariate correlations between species richness, crown complementarity, functional diversity and forest productivity. We employed linear mixed effects models to predict crown complementarity and examined its relationship with functional diversity. Finally, we applied structural equation modeling to quantify the mediation effects of crown complementarity on SRPRs. Species richness promoted crown complementarity and forest productivity. Crown complementarity varied across quadrats, with increases driven primarily by changes in tree height. Crown complementarity was positively related to functional diversity and forest productivity. Species richness increased with soil total phosphorus, while functional diversity decreased with soil bulk density. Forest productivity increased with soil organic carbon and total nitrogen, but decreased with bulk density. Crown complementarity partially mediated the positive effect of species richness on forest productivity, and the mediation effect was mainly through functional diversity. Our results suggest that the crown complementarity index accurately reflects the niche complementarity through light utilization and carbon reallocation. Our study emphasizes that species richness can promote crown complementarity, leading to greater forest productivity, which provides greater insight into the mechanical understanding of the SRPRs.

Starch accumulation dynamics and transcriptome analysis of Chlorella sorokiniana during transition of sulfur nutritional status

Microalgae can effectively accumulate starch by using nutritional limitation methods in the context of bioalcohol fuel production. However, relatively few studies have focused on starch accumulation in microalgae and its molecular basis, especially under sulfur limitation conditions. In this study, the starch accumulation dynamics and physiological responses of Chlorella sorokiniana under sulfur starvation (SS) and sulfur replenishment (SR) conditions were investigated, and the genes involved in the transcriptional regulation were explored using RNA-seq. The starch content in C. sorokiniana cells significantly increased from 1.6% to 55.0% of dry weight within 24 h under SS conditions, and then, it decreased to 3.4% within 12 h after transition to SR conditions. However, cell growth was inhibited, and pigment content decreased under SS conditions. Using RNA-seq analysis, a total of 9720 differentially expressed genes (DEGs) induced by sulfur status were obtained. These genes were narrowed down to 454 starvation and replenishment cross-validated (SRV)-DEGs, among which 283 SRV-DEGs were significantly up-regulated and 171 SRV-DEGs were down-regulated under SS conditions, and returned to their previous state under SR conditions. The SRV-DEGs enriched in the sulfate metabolism pathway were all up-regulated under SS conditions after 6 h to speed up the sulfur metabolic cycle, and the transcriptional abundance of a sulfate transporter (SULTR4), cysteine synthase[O-acetylserine(thiol)-lyase] (OASTL), serine acetyltransferase (SAT), and methanethiol oxidase (SELENBP1) increased 8.6-fold, 12.6-fold, 8.7-fold, and 12.4-fold, respectively. Protein synthesis was correspondingly inhibited, which resulted in the reallocation of carbon and elevated the starch synthesis pathway, in which the expressions of glycogen branching enzyme (GBE) and starch synthase (SS) were up-regulated 12.0- and 3.0-fold, respectively. The fatty acid desaturase (FAD) and phosphatidic acid phosphatase (PAP) in the lipid synthesis pathway were strongly up-regulated 8.8- and 16.2-fold, respectively, indicating the competitive synthesis of lipids. The down-regulation of SRV-DEGs associated with carbon fixation, such as those in the Calvin cycle, possibly affected cell growth. The time-resolved transcriptional analysis identified the SRV-DEGs, revealing the underlying starch accumulation mechanism, as well as the relationship with cell growth and lipid synthesis.

Leveraging CO2 to directionally control the H2/CO ratio in continuous microwave pyrolysis/gasification of waste plastics: Quantitative analysis of CO2 and density functional theory calculations of regulation mechanism

To recover syngas from waste plastics (Low-density polyethylene, LDPE) and CO2 simultaneously, the advanced continuous microwave pyrolysis and in situ reforming of CO2 were used. The ability of CO2 to tune LDPE carbon reallocation was evaluated, as was that of CO2 to directionally control the H2/CO ratio. The CO2 utilization efficiency and energy balance were quantitatively analysed, and the mechanism through which CO2 controlled H2/CO ratio was explored via experimental results and density functional theory calculations. The results showed that increasing pyrolysis temperature from 450 °C to 650 °C and introducing CO2 changed the carbon reallocation ability, increased syngas content, and controlled H2/CO ratio. The pyrolysis gas yield and syngas content reached the maximum values of 96.44% and 66.61 vol%, respectively. However, introducing excessive CO2 led to the double waste of resources and energy due to side reactions and high energy consumption. The maximum value of CO2 utilization efficiency and energy recovery efficiency was 78.95% (75 vol% CO2) and 75.09% (50 vol% CO2), respectively. CO2 directionally controlled the production of syngas and H2/CO ratio (from 0.65 to 2.88) by stimulating the LDPE pyrolysis reaction and the reforming reactions of its pyrolysis intermediates to form oxidized carbon radicals (such as Rn-O-C-O*, Rn-CO*, and Rn-O*) to generate CO. Therefore, different pyrolysis systems could regulate the degree of CO2 reforming reaction by controlling CO2 concentration based on the goal of optimizing the efficiency of resource or energy. This work provides basic theory and technical support for realizing the efficient recycling of waste plastics and CO2.

Differential Response of Two Tomato Genotypes, Wild Type cv. Ailsa Craig and Its ABA-Deficient Mutant flacca to Short-Termed Drought Cycles.

Two tomato genotypes with constitutively different ABA level, flacca mutant and wild type of Ailsa Craig cv. (WT), were subjected to three repeated drought cycles, with the aim to reveal the role of the abscisic acid (ABA) threshold in developing drought tolerance. Differential responses to drought of two genotypes were obtained: more pronounced stomatal closure, ABA biosynthesis and proline accumulation in WT compared to the mutant were compensated by dry weight accumulation accompanied by transient redox disbalance in flacca. Fourier-transform infrared (FTIR) spectra analysis of isolated cell wall material and morphological parameter measurements on tomato leaves indicated changes in dry weight accumulation and carbon re-allocation to cell wall constituents in flacca, but not in WT. A higher proportion of cellulose, pectin and lignin in isolated cell walls from flacca leaves further increased with repeated drought cycles. Different ABA-dependent stomatal closure between drought cycles implies that acquisition of stomatal sensitivity may be a part of stress memory mechanism developed under given conditions. The regulatory role of ABA in the cell wall restructuring and growth regulation under low leaf potential was discussed with emphasis on the beneficial effects of drought priming in developing differential defense strategies against drought.

Wild emmer introgression alters root-to-shoot growth dynamics in durum wheat in response to water stress

Water deficit during the early vegetative growth stages of wheat (Triticum) can limit shoot growth and ultimately impact grain productivity. Introducing diversity in wheat cultivars to enhance the range of phenotypic responses to water limitations during vegetative growth can provide potential avenues for mitigating subsequent yield losses. We tested this hypothesis in an elite durum wheat background by introducing a series of introgressions from a wild emmer (Triticum turgidum ssp. dicoccoides) wheat. Wild emmer populations harbor rich phenotypic diversity for drought-adaptive traits. To determine the effect of these introgressions on vegetative growth under water-limited conditions, we used image-based phenotyping to catalog divergent growth responses to water stress ranging from high plasticity to high stability. One of the introgression lines exhibited a significant shift in root-to-shoot ratio in response to water stress. We characterized this shift by combining genetic analysis and root transcriptome profiling to identify candidate genes (including a root-specific kinase) that may be linked to the root-to-shoot carbon reallocation under water stress. Our results highlight the potential of introducing functional diversity into elite durum wheat for enhancing the range of water stress adaptation.

Systematic metabolome profiling and multi-omics analysis of the nitrogen-limited non-model oleaginous algae for biorefining

Oleaginous microalga Chlorella is a promising microbial cell factory for producing lipids, transesterifiable to biodiesel, and phytochemical, high-value molecules (HVMs). To better understand the stress-induced oleaginous mechanism of Chlorella sp. FC2 IITG that closely matches with Chlorella sorokiniana based on 18s rRNA gene sequence, we performed 'Algomics' by systematically integrating metabolomics and proteomics data in response to time-resolved nitrogen-limitation: 40 h (mild), 88 h (moderate), and 120 h (severe). Ten HVMs belonging to four biological classes: triacylglycerol (TAG), polyunsaturated fatty acids (PUFA), phytosterols, and terpenoids were annotated using untargeted metabolomics and MS/MS fragmentation pattern match to the spectral library. In particular, the study evidenced 4× and 6× increased accumulation of two different PUFA: 9(S)HpOTrE and dihomo-gamma-linolenic acid, respectively, in nitrogen-limitation conditions. Co-extraction of TAG and PUFA could lower the biodiesel production cost for feasible commercialization. The investigation found a maximum accumulation of TAG 59:10 at 40 h, while that for TAG 54:4 was recorded at 88 h, which suggests different TAG species could be induced by regulating nitrogen-limitation severity. Elevated ꞵ-oxidation, glycolysis, and tricarboxylic acid (TCA) cycle identified in proteomics analysis could provide the substrates, phosphoenolpyruvate, pyruvate, and acetyl CoA, for different phytochemical accumulation in response to nitrogen limitation. The multiomics data unraveled a metabolic tug-of-war ongoing between biomass and storage lipid (TAG) accumulation during nitrogen-limitation, which involved multiple processes including hindered CO2 fixation, the supply of energy, reductants, and carbon reallocation from proteins and membrane lipids. These findings provide distinct oleaginous mechanisms in non-model microalgae, Chlorella sp. FC2 IITG, and engineerable targets for microalgal trait improvements.

Transcriptomic analysis of Chlorella sp. HS2 suggests the overflow of acetyl‐CoA and NADPH cofactor induces high lipid accumulation and halotolerance

AbstractPreviously, we isolated Chlorella sp. HS2 (referred hereupon as HS2) from a local tidal rock pool and demonstrated its halotolerance and high biomass productivity under different salinity conditions. To further understand acclimation responses of this alga under high salinity stress, we performed transcriptome analysis of triplicated culture samples grown in freshwater and marine conditions at both exponential and stationary growth phases. The results indicated that the transcripts involved in photosynthesis, TCA, and Calvin cycles were downregulated, whereas the upregulation of DNA repair mechanisms and an ABCB subfamily of eukaryotic type ABC transporter was observed at high salinity condition. In addition, while key enzymes associated with glycolysis pathway and triacylglycerol (TAG) synthesis were determined to be upregulated from early growth phase, salinity stress seemed to reduce the carbohydrate content of harvested biomass from 45.6 dw% to 14.7 dw% and nearly triple the total lipid content from 26.0 dw% to 62.0 dw%. These results suggest that the reallocation of storage carbon toward lipids played a significant role in conferring the viability of this alga under high salinity stress by remediating high level of cellular stress partially resulted from ROS generated in oxygen‐evolving thylakoids as observed in a direct measure of photosystem activities.

Split-root investigation of the physiological response to heterogeneous elevated Zn exposure in poplar and willow

Essential and toxic ions are often heterogeneously distributed within a soil landscape. This fact may complicate phytoextraction efforts to remove toxic ions such as heavy metals from the soil as the roots of some plants instead may colonize more favorable microenvironments and avoid heavy metal accumulation. In this study a split-root hydroponic experiment was used to test whether root-level exposure to zinc (Zn) stress to none, half or all of the root systems of Populus deltoides Bart. ex Marshall x Populus nigra L. (poplar) and Salix matsudana L. (willow) plants alters root and shoot physiology. Cuttings of both species were split to create two root system halves that were exposed to either control (-Zn) or stress (+1 mM Zn) solutions for 42 days. Weekly measurements of gas exchange, photosystem fluorescence parameters and pigments showed that poplar was more sensitive to the half stress (-Zn/+Zn) treatment than willow, with lower gas exchange rates and total chlorophyll and carotenoid values relative to their respective controls (-Zn/-Zn). Half stress willow plants had increased root growth in the half without Zn, demonstrating a reallocation of carbon to compensate with no negative impact to shoot physiology as compared to poplar. Water consumption was also reduced in half stress willow but not in poplar, suggesting an increase in water-use efficiency in response to heterogeneous Zn exposure that was not derived from dramatic reductions in transpiration rate. These significant differences between these two species in response to patchy distribution of toxic Zn concentration may impact the efficiency of phytoremediation efforts and suggests additional criteria to consider in the pre-selection process.

Triple-localized WHIRLY2 Influences Leaf Senescence and Silique Development via Carbon Allocation.

Coordination of gene expression in mitochondria, plastids, and nucleus is critical for plant development and survival. Although WHIRLY2 (WHY2) is involved in mitochondrial genome repair and affects the DNA copy number of the mitochondrial genome, the detailed mechanism of action of the WHY2 protein is still elusive. In this study, we found that WHY2 was triple-localized among the mitochondria, plastids, and the nucleus during Arabidopsis (Arabidopsis thaliana) aging. Overexpressing WHY2 increased starch granule numbers in chloroplasts of pericarp cells, showing a partially dry, yellowing silique and early senescence leaves. Accordingly, WHY2 protein could directly activate the expression of jasmonic acid carboxyl methyltransferase and senescence associated gene 29 (SWEET15) gene expression and repress SWEET11 gene expression in the nucleus, leading to alteration of starch accumulation and transport in pericarp cells. In contrast, loss of WHY2 decreased starch and sugar content in pericarp cells but promoted starch accumulation in leaves and seeds. These phenotypes of WHY2-overexpressing plants were enhanced in response to methyl jasmonate. Our results suggest that WHY2 in plastids, mitochondria, and the nucleus plays a vital role in alteration of carbon reallocation from maternal tissue to filial tissue.

Sargassum stenophyllum (Fucales, Ochrophyta) responses to temperature short-term exposure: photosynthesis and chemical composition

Sargassum species form extensive benthic beds in tropical and subtropical low intertidal and subtidal zones, acting as important drivers for marine community structure. Temperature, as one of the most important abiotic factor, affects seaweed performance and triggers changes in metabolic responses; therefore, laboratory experiments involving temperature ranges are tools for understanding seaweed engineering. The aim of this study was to assess the physiological vulnerability and sensitivity of Sargassum stenophyllum C. Martius exposed to five different temperatures by analyzing photosynthetic performance and chemical composition related to carbon and nitrogen metabolism. There were no significant differences in energy quenching between treatments, except at 35 °C, which showed decreased photochemical quenching and increased non-regulated non-photochemical quenching. Chlorophyll a and chlorophyll c at 15 °C and 35 °C exhibited lower amounts at the end of experiment. Protein content showed progressive diminution in the treatments. Total soluble carbohydrates content showed higher concentration as temperature increased. After 7 days, total amino acid content showed increase from 15 °C to 30 °C. No generalization between the amino acid patterns, although glutamine and glutamate content at 15 °C and 35 °C were reduced; and the highest values of isoleucine and leucine were detected at 35 °C. We postulated that accumulation of certain chemical compounds in S. stenophyllum results from a reallocation of carbon and nitrogen, osmoregulation responses and protection against oxidative stress. Results suggest this species’ tolerance ranges between 15 °C and 30 °C and sensitivity at 35 °C.

Time\u2011resolved transcriptome analysis during transitions of sulfur nutritional status provides insight into triacylglycerol (TAG) and astaxanthin accumulation in the green alga Chromochloris zofingiensis

BackgroundChromochloris zofingiensis, an oleaginous microalga, is a promising feedstock for the co-production of triacylglycerol (TAG)-based biodiesel and the high-value product astaxanthin. To reveal the molecular mechanism of TAG and astaxanthin biosynthesis during transitions of sulfur nutritional status, namely sulfur-starvation (SS) and sulfur-replenishment (SR), the physiological responses and the transcriptomic dynamics of C. zofingiensis were examined.ResultsThe results revealed a reversible TAG and astaxanthin accumulation under SS, which is correlated with the reduction of cell growth and protein content, indicating the reallocation of carbon. By correlating the data on the physiological and transcriptional responses to different sulfur nutritional status, a model for the underlying mechanism of TAG and astaxanthin accumulation in C. zofingiensis was postulated, which involved up-regulation of key genes including diacylglycerol acyltransferase (DGTT5) and beta-carotene ketolase (BKT1), increased energy and NADPH supply by elevating the tricarboxylic acid (TCA) cycle and the oxidative pentose phosphate (OPP) pathway, and the increased carbon precursors (pyruvate and acetyl-CoA) through central carbon metabolism. In addition, the net enhancement of the de novo biosynthesis of fatty acids and the re-direction of the terpenoid precursors toward the branch catalyzed by lycopene beta cyclase (LCYb) and BKT1 escalated the substrate availability for the biosynthesis of TAG and astaxanthin, respectively.ConclusionsIn this study, the time-resolved transcriptional analysis of C. zofingiensis under SS and SR conditions was reported for the first time to elucidate the regulatory roles of key enzymes, including DGTT5, BKT1 and LCYb, in the underlying mechanisms of TAG and astaxanthin accumulation.

Time-resolved multi-omics analysis reveals the role of nutrient stress-induced resource reallocation for TAG accumulation in oleaginous fungus Mortierella alpina

BackgroundGlobal resource reallocation is an established critical strategy through which organisms deal with environmental stress. The regulation of intracellular lipid storage or utilization is one of the most important strategies for maintaining energy homeostasis and optimizing growth. Oleaginous microorganisms respond to nitrogen deprivation by inducing lipid hyper accumulation; however, the associations between resource allocation and lipid accumulation are poorly understood.ResultsHere, the time-resolved metabolomics, lipidomics, and proteomics data were generated in response to nutrient availability to examine how metabolic alternations induced by nitrogen deprivation drive the triacylglycerols (TAG) accumulation in M. alpina. The subsequent accumulation of TAG under nitrogen deprivation was a consequence of the reallocation of carbon, nitrogen sources, and lipids, rather than an up-regulation of TAG biosynthesis genes. On one hand, nitrogen deprivation induced the down-regulation of isocitrate dehydrogenase level in TCA cycle and redirected glycolytic flux of carbon from amino acid biosynthesis into fatty acids’ synthesis; on the other hand, nitrogen deprivation induced the up-regulation of cell autophagy and ubiquitin-mediated protein proteolysis which resulted in a recycling of preformed protein nitrogen and carbon. Combining with the up-regulation of glutamate decarboxylase and succinic semialdehyde dehydrogenase in GABA shunt, and the phosphoenolpyruvate carboxykinase in the central hub involving pyruvate/phosphoenolpyruvate/oxaloacetate, the products from nitrogen-containing compounds degradation were recycled to be intermediates of TCA cycle and be shunted toward de novo biosynthesis of fatty acids. We found that nitrogen deprivation increased the protein level of phospholipase C/D that contributes to degradation of phosphatidylcholine and phosphatidylethanolamine, and supplied acyl chains for TAG biosynthesis pathway. In addition, ATP from substrate phosphorylation was presumed to be a critical factor regulation of the global resource allocation and fatty acids’ synthesis rate.ConclusionsThe present findings offer a panoramic view of resource allocation by M. alpina in response to nutrient stress and revealed a set of intriguing associations between resource reallocation and TAG accumulation. This system-level insight provides a rich resource with which to explore in-depth functional characterization and gain information about the strategic combination of strain development and process integration to achieve optimal lipid productivity under nutrient stress.

Metabolic regulations in lettuce root under combined exposure to perfluorooctanoic acid and perfluorooctane sulfonate in hydroponic media

Per- and polyfluoroalkyl substances (PFASs) have been detected in many agricultural products in contaminated fields and in supply chains. Roots are the main organ in plants to uptake and bio-accumulate PFASs, but the changes of metabolic regulation in roots by PFASs are largely unexplored. Here, lettuce exposed to perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) at different concentrations (500, 1000, 2000 and 5000 ng/L) was investigated via metabolomics. Many key metabolites, such as antioxidants, lipids, amino acids, fatty acids, carbohydrates, linolenic acid derivatives, purine and nucleosides, were significantly altered. Tyrosine metabolism, purine metabolism, isoquinoline alkaloid biosynthesis and terpenoid backbone biosynthesis were altered in roots by PFOA and PFOS. Tricarboxylic acid cycle was perturbed by 5000 ng/L exposure. Activation of antioxidant defense pathways, reallocation of carbon and nitrogen metabolism, regulation of energy metabolism and purine metabolism were reprogrammed in roots. Lettuce employed multiple strategies to increase tolerance to PFOA and PFOS, which includes the adjustment of membrane composition, elevation of inorganic nitrogen fixation and respiration, accumulation of sucrose and regulation of signaling molecules. The results of this study offer insights into the molecular reprogramming of plant roots in response to PFAS exposure and provide important information for the risk assessment of PFASs in environment.

Use of steel slag as a catalyst in CO2-cofeeding pyrolysis of pine sawdust

To seek an innovative way for simultaneous waste management and energy recovery, two waste materials (pine sawdust: PSD and steel slag: SS) were used in the pyrolysis process. PSD was used as a carbonaceous material for pyrolysis, and SS was used as a catalyst. Also, to achieve a more sustainable conversion system, a viable use of carbon dioxide (CO2) as a raw material in the non-catalytic/catalytic pyrolysis process was evaluated. Hence, the present study laid great stress on the CO2 effects. The present study pointed the optimistic technical features in line with the use of CO2 in the pyrolysis process. Exploiting CO2 in pyrolysis of PSD offered a strategic way to control carbon reallocation from liquid to gaseous pyrolysates by the gas phase reactions (GPRs). The reactions of CO2 and volatile pyrolysates led to CO enhancement, which was only observed at ≥ 600 °C due to the slow reaction kinetics of the GPRs of volatile pyrolysates and CO2. Such the slow reaction kinetics was expedited remarkably when SS was acted as a catalyst. Moreover, CO2 expedited thermal cracking of volatile pyrolysates including dehydrogenation, which led to the enhanced formation of CH4 and H2.

Multiomics analysis reveals a distinct mechanism of oleaginousness in the emerging model alga Chromochloris zofingiensis.

Chromochloris zofingiensis, featured due to its capability to simultaneously synthesize triacylglycerol (TAG) and astaxanthin, is emerging as a leading candidate alga for production uses. To better understand the oleaginous mechanism of this alga, we conducted a multiomics analysis by systematically integrating time-resolved transcriptomes, lipidomes and metabolomes in response to nitrogen deprivation. The data analysis unraveled the distinct mechanism of TAG accumulation, which involved coordinated stimulation of multiple biological processes including supply of energy and reductants, carbon reallocation from protein and starch, and 'pushing' and 'pulling' carbon to TAG synthesis. Unlike the model alga Chlamydomonas, de novo fatty acid synthesis in C.zofingiensis was promoted, together with enhanced turnover of both glycolipids and phospholipids, supporting the drastic need of acyls for TAG assembly. Moreover, genomewide analysis identified many key functional enzymes and transcription factors that had engineering potential for TAG modulation. Two genes encoding glycerol-3-phosphate acyltransferase (GPAT), the first committed enzyme for TAG assembly, were found in the C.zofingiensis genome; invivo functional characterization revealed that extrachloroplastic GPAT instead of chloroplastic GPAT played a central role in TAG synthesis. These findings illuminate distinct oleaginousness mechanisms in C.zofingiensis and pave the way towards rational manipulation of this alga to becone an emerging model for trait improvements.