Regulation of sucrose metabolism in higher plants: localization and regulation of activity of key enzymes

Genome-wide identification and characterization of the sucrose invertase gene family in Hemerocallis citrina

Background

Sucrose invertase is an important catalytic enzyme that is widely distributed in plants and can irreversibly hydrolyze sucrose into fructose and glucose. Daylily is an important perennial flower worldwide and a traditional vegetable in East Asia. Previous studies have suggested that sucrose invertase is involved in the aging of daylily flowers. However, knowledge about the number, physicochemical properties, and expression patterns of daylily sucrose invertases is still lacking. Identifying the daylily sucrose invertase family genes in the genome is highly important for understanding phylogenetic evolution and determining the genetic function of sucrose invertase.

Methods

To obtain basic knowledge about the number, classification, sequence composition, and physicochemical properties of sucrose invertases in daylily, bioinformatics software was used to analyze the genome of Hemerocallis citrina (H. citrina), and the basic properties of sucrose invertase genes and proteins were obtained. Then, combined with transcriptome data from flower organs at different developmental stages, the expression patterns of each gene were clarified. Finally, the reliability of the transcriptome data was verified by quantitative real-time polymerase chain reaction (PCR).

Results

Through software analysis, 35 sucrose invertases were identified from the H. citrina genome and named HcINV1-HcINV35; these enzymes belong to three subfamilies: cell wall invertases, vacuolar invertases, and chloroplast invertases. The amino acid composition, motif types, promoter composition, gene structure, protein physicochemical properties, gene chromosomal localization, and evolutionary adaptability of daylily invertases were determined; these results provided a comprehensive understanding of daylily invertases. The transcriptome expression profile combined with fluorescence quantitative reverse transcription-polymerase chain reaction (RT‒PCR) analysis suggested that almost all daylily invertase genes were expressed in flower organs, but even genes belonging to the same subfamily did not exhibit the same expression pattern at different developmental stages, suggesting that there may be redundancy or dissimilation in the function of daylily sucrose invertases.

Combination of transcriptomic, biochemical, and physiological analyses reveals sugar metabolism in Camellia drupifera fruit at different developmental stages

Camellia drupifera, a significant woody oil crop in southern China, produces oil from its fruit seeds. Understanding sugar metabolism enzyme regulation is crucial for sugar accumulation and oil synthesis in fruit organs. This study examines the dynamic changes in sugar metabolism across four developmental stages of C. drupifera fruits, from rapid fruit enlargement to oil conversion. We analyzed sugar content, enzyme activity, and transcriptomic data to identify key periods and mechanisms involved in sugar metabolism. Our findings indicate that photosynthetic products are rapidly transported from leaves to fruit organs after synthesis, with transport efficiency decreasing significantly after 48 hours. September was identified as a critical period for oil conversion, during which the highest sucrose levels and SuSy-II enzyme activity were detected in the kernels. A positive correlation was found between high expression of ten genes related to sugar metabolism enzymes and sugar transport proteins and sucrose content. Notably, the expression levels of c158337.graph_c0 (SPS), c166323.graph_c0 (SuSy), c159295.graph_c0 (SUC2-like), and c156402.graph_c0 (SUC2-like) significantly increased during the oil conversion phase.These findings provide a crucial theoretical foundation for elucidating the molecular mechanisms of sugar metabolism in C. drupifera fruits, offering insights that could enhance its economic yield.

ALA Promotes Sucrose Accumulation in Early Peach Fruit by Regulating SPS Activity

5-Aminolevulinic acid (ALA), as a novel plant growth regulator, is a critical precursor for the biosynthesis of porphyrin compounds in all organisms. Many studies have reported that exogenous ALA treatment could improve fruit sweetness. However, the mechanism by which ALA promotes the increase in sugar content in fruit remains unclear. In this study, we found that ALA significantly promoted sucrose accumulation and SPS (sucrose phosphate synthase) activity in peach fruit. At 14, 28, 42, 50 and 60 days after ALA treatment, sucrose content of fruit was increased by 23%, 43%, 37%, 40% and 16%, respectively, compared with control treatment, and SPS enzyme activity was increased by 21%, 28%, 47%, 37% and 29%, respectively. Correlation analysis showed that the sucrose content of peach fruit under ALA treatment was significantly positively correlated with SPS activity. Subsequently, bioinformatics was used to identify SPS gene family members in peach fruit, and it was found that there were four members of the PpSPS gene family, distributed on chromosomes 1, 7 and 8, named PpSPS1, PpSPS2, PpSPS3 and PpSPS4, respectively. The results of qRT-PCR showed that PpSPS2 and PpSPS3 were highly expressed in response to ALA during fruit development, and the expression of PpSPS2 was positively correlated with SPS activity and sucrose accumulation in peach fruit. The results of tobacco subcellular localization showed that PpSPS2 was mainly distributed in the cytoplasm and nucleus, while PpSPS3 was mainly distributed in the nucleus. The results of this study will lay the foundation for further study on the functions of PpSPS and the regulation of sugar metabolism during the development and ripening of peach fruit by ALA.

Overexpressing GLUTAMINE SYNTHETASE 1;2 maintains carbon and nitrogen balance under high-ammonium conditions and results in increased tolerance to ammonium toxicity in hybrid poplar

The glutamine synthetase/glutamic acid synthetase (GS/GOGAT) cycle plays important roles in N metabolism, growth, development, and stress resistance in plants. Excess ammonium (NH4+) restricts growth, but GS can help to alleviate its toxicity. In this study, the 84K model clone of hybrid poplar (Populus alba × P. tremula var. glandulosa), which has reduced biomass accumulation and leaf chlorosis under high-NH4+ stress, showed less severe symptoms in transgenic lines overexpressing GLUTAMINE SYNTHETASE 1;2 (GS1;2-OE), and more severe symptoms in RNAi lines (GS1;2-RNAi). Compared with the wild type, the GS1;2-OE lines had increased GS and GOGAT activities and higher contents of free amino acids, soluble proteins, total N, and chlorophyll under high-NH4+ stress, whilst the antioxidant and NH4+ assimilation capacities of the GS1;2-RNAi lines were decreased. The total C content and C/N ratio in roots and leaves of the overexpression lines were higher under stress, and there were increased contents of various amino acids and sugar alcohols, and reduced contents of carbohydrates in the roots. Under high-NH4+ stress, genes related to amino acid biosynthesis, sucrose and starch degradation, galactose metabolism, and the antioxidant system were significantly up-regulated in the roots of the overexpression lines. Thus, overexpression of GS1;2 affected the carbon and amino acid metabolism pathways under high-NH4+ stress to help maintain the balance between C and N metabolism and alleviate the symptoms of toxicity. Modification of the GS/GOGAT cycle by genetic engineering is therefore a potential strategy for improving the NH4+ tolerance of cultivated trees.

Nitrogen inhibition of nitrogenase activity involves the modulation of cytosolic invertase in soybean nodule

Legume symbiotic nitrogen fixation (SNF) is suppressed by inorganic nitrogen (N) in the soil. High N inhibition of nitrogenase activity is associated with the deprivation of carbon allocation and metabolism in nodules. However, the underlying molecular mechanisms remain unclear. Here, we identify GmCIN1 which encodes a cytosolic invertase, as a gateway for the N-tuning of sucrose utilization in nodules. GmCIN1 is enriched in mature soybean nodules and its expression is regulated by nitrogen status. The knockout of GmCIN1 using genome editing partially mimics the inhibitory effects of N on nitrogenase activity and sugar content and the impact of high N on nodule transcriptomes. This indicates that GmCIN1 partially mediates the high N inhibition of nodule activity. Moreover, ChIP-qPCR and EMSA reveal that SNAP1/2 transcription factors directly bind to the GmCIN1 promoter. In addition, SNAP1/2 may be involved in the repression of GmCIN1 expression in mature nodules at high N concentrations. Our findings provide insights into the involvement of the transcriptional tuning of carbon (C) metabolism genes by N-signaling modulators in the N-induced inhibition of nitrogenase activity.

Short-term salt stress reduces photosynthetic oscillations under triose phosphate utilization limitation in tomato

Triose phosphate utilization (TPU) limitation is one of the three biochemical limitations of photosynthetic CO2 assimilation rate in C3 plants. Under TPU limitation, abrupt and large transitions in light intensity cause damped oscillations in photosynthesis. When plants are salt-stressed, photosynthesis is often down-regulated particularly under dynamic light intensity, but how salt stress affects TPU-related dynamic photosynthesis is still unknown. To elucidate this, tomato (Solanum lycopersicum) was grown with and without sodium chloride (NaCl, 100 mM) stress for 13 d. Under high CO2 partial pressure, rapid increases in light intensity caused profound photosynthetic oscillations. Salt stress reduced photosynthetic oscillations in leaves initially under both low- and high-light conditions and reduced the duration of oscillations by about 2 min. Besides, salt stress increased the threshold for CO2 partial pressure at which oscillations occurred. Salt stress increased TPU capacity without affecting Rubisco carboxylation and electron transport capacity, indicating the up-regulation of end-product synthesis capacity in photosynthesis. Thus salt stress may reduce photosynthetic oscillations by decreasing leaf internal CO2 partial pressure and/or increasing TPU capacity. Our results provide new insights into how salt stress modulates dynamic photosynthesis as controlled by CO2 availability and end-product synthesis.

Analysis of sugar components and identification of SPS genes in citrus fruit development

Sugar is a primary determinant of citrus fruit flavour, but undergoes varied accumulation processes across different citrus varieties owing to high genetic variability. Sucrose phosphate synthase (SPS), a key enzyme in glucose metabolism, plays a crucial role in this context. Despite its significance, there is limited research on sugar component quality and the expression and regulatory prediction of SPS genes during citrus fruit development. Therefore, we analysed the sugar quality formation process in 'Kiyomi' and 'Succosa', two citrus varieties, and performed a comprehensive genome-wide analysis of citrus CsSPSs. We observed that the accumulation of sugar components significantly differs between the two varieties, with the identification of four CsSPSs in citrus. CsSPS sequences were highly conserved, featuring typical SPS protein domains. Expression analysis revealed a positive correlation between CsSPS expression and sugar accumulation in citrus fruits. However, CsSPS expression displays specificity to different citrus tissues and varieties. Transcriptome co-expression network analysis suggests the involvement of multiple transcription factors in shaping citrus fruit sugar quality through the regulation of CsSPSs. Notably, the expression levels of four CsWRKYs (CsWRKY2, CsWRKY20, CsWRKY28, CsWRKY32), were significantly positively correlated with CsSPSs and CsWRKY20 might can activate sugar accumulation in citrus fruit through CsSPS2. Collectively, we further emphasize the potential importance of CsWRKYs in citrus sugar metabolism, our findings serve as a reference for understanding sugar component formation and predicting CsSPS expression and regulation during citrus fruit development.

Metabolic changes during wheat microspore embryogenesis induction using the highly responsive cultivar Svilena

Androgenetically-derived haploids can be obtained by inducing embryogenesis in microspores. Thus, full homozygosity is achieved in a single generation, oppositely to conventional plant breeding programs. Here, the metabolite profile of embryogenic microspores of Triticum aestivum was acquired and integrated with transcriptomic existing data from the same samples in an effort to identify the key metabolic processes occurring during the early stages of microspore embryogenesis. Primary metabolites and transcription profiles were identified at three time points: prior to and immediately following a low temperature pre-treatment given to uninuclear microspores, and after the first nuclear division. This is the first time an integrative -omics analysis is reported in microspore embryogenesis in T. aestivum. The key findings were that the energy produced during the pre-treatment was obtained from the tricarboxylic acid (TCA) cycle and from starch degradation, while starch storage resumed after the first nuclear division. Intermediates of the TCA cycle were highly demanded from a very active amino acid metabolism. The transcription profiles of genes encoding enzymes involved in amino acid synthesis differed from the metabolite profiles. The abundance of glutamine synthetase was correlated with that of glutamine. Cytosolic glutamine synthetase isoform 1 was found predominantly after the nuclear division. Overall, energy production was shown to represent a major component of the de-differentiation process induced by the pre-treatment, supporting a highly active amino acid metabolism.

Increased DNA methylation of the splicing regulator SR45 suppresses seed abortion in litchi

The gene regulatory networks that govern seed development are complex, yet very little is known about the genes and processes that are controlled by DNA methylation. Here, we performed single-base resolution DNA methylome analysis and found that CHH methylation increased significantly throughout seed development in litchi. Based on the association analysis of differentially methylated regions and weighted gene co-expression network analysis (WGCNA), 46 genes were identified as essential DNA methylation-regulated candidate genes involved in litchi seed development, including LcSR45, a homolog of the serine/arginine-rich (SR) splicing regulator SR45. LcSR45 is predominately expressed in the funicle, embryo, and seed integument, and displayed increased CHH methylation in the promoter during seed development. Notably, silencing of LcSR45 in a seed-aborted litchi cultivar significantly improved normal seed development, whereas the ectopic expression of LcSR45 in Arabidopsis caused seed abortion. Furthermore, LcSR45-dependent alternative splicing events were found to regulate genes involved in seed development. Together, our findings demonstrate that LcSR45 is hypermethylated, and plays a detrimental role in litchi seed development, indicating a global increase in DNA methylation at this stage.

Overexpression of ZmSUS1 increased drought resistance of maize (Zea mays L.) by regulating sucrose metabolism and soluble sugar content

MAIN CONCLUSION

ZmSUS1 improved drought tolerance of maize by regulating sucrose metabolism and increasing soluble sugar content, and endowing transgenic maize with higher relative water content and photosynthesis levels. Sucrose synthase (SUS), a key enzyme of sugar metabolism, plays an important role in the regulation of carbon partitioning in plant, and affects important agronomic traits and abiotic responses to adversity. However, the function of ZmSUS1 in plant drought tolerance is still unknown. In this study, the expression patterns of ZmSUS1 in different tissues and under drought stress were analyzed in maize (Zea mays L.). It was found that ZmSUS1 was highly expressed during kernel development but also in leaves and roots of maize, and ZmSUS1 was induced by drought stress. Homozygous transgenic maize lines overexpressing ZmSUS1 increased the content and activity of SUS under drought stress and exhibited higher relative water content, proline and abscisic acid content in leaves. Specifically, the net photosynthetic rate and the soluble sugar contents including sucrose, glucose, fructose and SUS decomposition products including UDP-glucose (UDP-G) and ADP-glucose (ADP-G) in transgenic plants were significantly improved after drought stress. RNA-seq analysis showed that overexpressing of ZmSUS1 mainly affected the expression level of carbon metabolism-related genes. Especially the expression level of sucrose metabolism-related genes including sucrose phosphatase gene (SPP), sucrose phosphate synthase gene (SPS) and invertase gene (INV) were significantly up-regulated in transgenic maize. Overall, these results suggested that ZmSUS1 improved drought tolerance by regulating sucrose metabolism and increasing the soluble sugar content, and endowing transgenic maize with higher relative water content and photosynthesis levels, which can serve as a new gene candidate for cultivating drought-resistant maize varieties.

H2 S works synergistically with rhizobia to modify photosynthetic carbon assimilation and metabolism in nitrogen-deficient soybeans

Hydrogen sulfide (H₂ S) performs a crucial role in plant development and abiotic stress responses by interacting with other signalling molecules. However, the synergistic involvement of H₂ S and rhizobia in photosynthetic carbon (C) metabolism in soybean (Glycine max) under nitrogen (N) deficiency has been largely overlooked. Therefore, we scrutinised how H₂ S drives photosynthetic C fixation, utilisation, and accumulation in soybean-rhizobia symbiotic systems. When soybeans encountered N deficiency, organ growth, grain output, and nodule N-fixation performance were considerably improved owing to H₂ S and rhizobia. Furthermore, H₂ S collaborated with rhizobia to actively govern assimilation product generation and transport, modulating C allocation, utilisation, and accumulation. Additionally, H₂ S and rhizobia profoundly affected critical enzyme activities and coding gene expressions implicated in C fixation, transport, and metabolism. Furthermore, we observed substantial effects of H₂ S and rhizobia on primary metabolism and C-N coupled metabolic networks in essential organs via C metabolic regulation. Consequently, H₂ S synergy with rhizobia inspired complex primary metabolism and C-N coupled metabolic pathways by directing the expression of key enzymes and related coding genes involved in C metabolism, stimulating effective C fixation, transport, and distribution, and ultimately improving N fixation, growth, and grain yield in soybeans.

Polar Metabolites Profiling of Wheat Shoots (Triticum aestivum L.) under Repeated Short-Term Soil Drought and Rewatering

The response of wheat (Triticum aestivum L.) plants to the soil drought at the metabolome level is still not fully explained. In addition, research focuses mainly on single periods of drought, and there is still a lack of data on the response of plants to short-term cyclical periods of drought. The key to this research was to find out whether wheat shoots are able to resume metabolism after the stress subsides and if the reaction to subsequent stress is the same. Gas chromatography coupled with mass spectrometry (GC-MS) is one of the most valuable and fast methods to discover changes in the primary metabolism of plants. The targeted GC-MS analyses of whole shoots of wheat plants exposed (at the juvenile stage of development) to short-term (five days) mild soil drought/rewatering cycles (until the start of shoot wilting) enabled us to identify 32 polar metabolites. The obtained results revealed an accumulation of sugars (sucrose, fructose, glucose, and 1-kestose), proline, and malic acid. During five days of recovery, shoots regained full turgor and continued to grow, and the levels of accumulated metabolites decreased. Similar changes in metabolic profiles were found during the second drought/rewatering cycle. However, the concentrations of glucose, proline, and malic acid were higher after the second drought than after the first one. Additionally, the concentration of total polar metabolites after each plant rewatering was elevated compared to control samples. Although our results confirm the participation of proline in wheat responses to drought, they also highlight the responsiveness of soluble carbohydrate metabolism to stress/recovery.

Arabidopsis thaliana Sucrose Phosphate Synthase A2 Affects Carbon Partitioning and Drought Response

Sucrose is essential for plants for several reasons: It is a source of energy, a signaling molecule, and a source of carbon skeletons. Sucrose phosphate synthase (SPS) catalyzes the conversion of uridine diphosphate glucose and fructose-6-phosphate to sucrose-6-phosphate, which is rapidly dephosphorylated by sucrose phosphatase. SPS is critical in the accumulation of sucrose because it catalyzes an irreversible reaction. In Arabidopsis thaliana, SPSs form a gene family of four members, whose specific functions are not clear yet. In the present work, the role of SPSA2 was investigated in Arabidopsis under both control and drought stress conditions. In seeds and seedlings, major phenotypic traits were not different in wild-type compared with spsa2 knockout plants. By contrast, 35-day-old plants showed some differences in metabolites and enzyme activities even under control conditions. In response to drought, SPSA2 was transcriptionally activated, and the divergences between the two genotypes were higher, with spsa2 showing reduced proline accumulation and increased lipid peroxidation. Total soluble sugars and fructose concentrations were about halved compared with wild-type plants, and the plastid component of the oxidative pentose phosphate pathway was activated. Unlike previous reports, our results support the involvement of SPSA2 in both carbon partitioning and drought response.

Overexpression of the ZmSUS1 gene alters the content and composition of endosperm starch in maize (Zea mays L.)

ZmSUS1 increases the amylose content of maize by regulating the expression of Shrunken2 (Sh2) and Brittle2 (Bt2) which encode the size subunits of endosperm ADP-glucose pyrophosphorylase, and Granule bound starchsynthase1 (GBSS1) and Starch synthase1 (SS1). Cereal crops accumulate starch in seeds as an energy reserve. Sucrose Synthase (SuSy) plays an important role in grain starch synthesis. In this study, ZmSUS1 was transformed into maize inbred line KN5585, and transgenic plants were obtained. Compared with the non-transgenic negative control, the content and activity of SuSy were significantly increased, the amylose content in mature seeds of transgenic maize increased by 41.1-69.2%, the total starch content increased by 5.0-13.5%, the 100-grain weight increased by 19.0-26.2% and the average diameter of starch granules increased by 10.8-17.2%. These results indicated that overexpression of ZmSUS1 can significantly improve the traits of maize seeds and obtain new lines with high amylose content. It was also found that the overexpression of ZmSUS1 may increase the amylose content by altering the expression of endosperm ADP-glucose pyrophosphorylase (AGPase) subunits Shrunken2 (Sh2) and Brittle2 (Bt2). Moreover, the ectopic expression of ZmSUS1 also affected the expression of Granule bound starch synthase1 (GBSS1) and Starch synthase1 (SS1) which encode starch synthase. This study proved the important role of ZmSUS1 in maize starch synthesis and provided a new technology strategy for improving maize starch content and yield.

Cyanobacteria as cell factories for the photosynthetic production of sucrose

Biofuels and other biologically manufactured sustainable goods are growing in popularity and demand. Carbohydrate feedstocks required for industrial fermentation processes have traditionally been supplied by plant biomass, but the large quantities required to produce replacement commodity products may prevent the long-term feasibility of this approach without alternative strategies to produce sugar feedstocks. Cyanobacteria are under consideration as potential candidates for sustainable production of carbohydrate feedstocks, with potentially lower land and water requirements relative to plants. Several cyanobacterial strains have been genetically engineered to export significant quantities of sugars, especially sucrose. Sucrose is not only naturally synthesized and accumulated by cyanobacteria as a compatible solute to tolerate high salt environments, but also an easily fermentable disaccharide used by many heterotrophic bacteria as a carbon source. In this review, we provide a comprehensive summary of the current knowledge of the endogenous cyanobacterial sucrose synthesis and degradation pathways. We also summarize genetic modifications that have been found to increase sucrose production and secretion. Finally, we consider the current state of synthetic microbial consortia that rely on sugar-secreting cyanobacterial strains, which are co-cultivated alongside heterotrophic microbes able to directly convert the sugars into higher-value compounds (e.g., polyhydroxybutyrates, 3-hydroxypropionic acid, or dyes) in a single-pot reaction. We summarize recent advances reported in such cyanobacteria/heterotroph co-cultivation strategies and provide a perspective on future developments that are likely required to realize their bioindustrial potential.

Comparative Physiological and Transcriptome Analysis Reveal the Molecular Mechanism of Melatonin in Regulating Salt Tolerance in Alfalfa (Medicago sativa L.)

As a high-quality legume forage, alfalfa is restricted by various abiotic stresses during its growth and development. Melatonin is a multifunctional signaling molecule that involves in plant defense against multiple stresses. However, little is known about its downstream signaling pathway and regulatory mechanisms in salt stress of alfalfa. In this study, we investigated the protective effects and key regulatory pathways of melatonin on alfalfa under salt tolerance. The results showed that melatonin promoted the growth of alfalfa seedlings under salt stress, as demonstrated by higher plant height, leaf area, and fresh weight. Melatonin treatment resulted in an increase in the photosynthetic capacity and starch content of alfalfa. Moreover, melatonin decreased cell membrane damage and reactive oxygen species (ROS) accumulation by enhancing antioxidant defense activity under salt stress conditions. Transcriptome sequencing (RNA-seq) analysis revealed that melatonin mainly induced the transcription of genes involved in Ca²⁺ signaling (cyclic nucleotide gated channel, CNGCs; cam modulin/calmodulin-like protein, CAM/CMLs and calcium-dependent protein kinase, CDPKs), starch and sucrose metabolism (α-amylase, AMYs; β-amylase, BAMs; starch synthase, SSs and sucrose synthase, SUSs), plant hormone signal transduction (auxin/indole acetic acid protein, AUX/IAAs; ABA receptor, PYL4; protein phosphatase 2C, PP2Cs; scarecrow-like protein, SCLs and ethylene-responsive transcription factor 1B, ERF1B), and key transcription factors (C3Hs, MYBs, ERFs, and WRKYs). Specifically, we focused on starch and sucrose metabolism and plant hormone signal transduction pathways. The interactions between melatonin and other phytohormones occurred via regulation of the expression of genes involved in hormone signaling pathways. In addition, melatonin increased the contents of endogenous melatonin, auxin, gibberellic acid (GA₃), salicylic acid, brassinosteroids, and ethylene, while decreasing the abscisic acid content under salt stress. In summary, this study established a regulatory network for melatonin-induced key signaling pathways and functional genes under salt stress and provided a theoretical basis for salt tolerance breeding in alfalfa.

The regulatory role of CARBON STARVED ANTHER-mediated photoperiod-dependent male fertility in rice

Environmental signals, especially daylength, play important roles in determining fertility in photoperiod-sensitive genic male sterile (PGMS) lines that are critical to sustain production of high-yielding hybrid rice (Oryza sativa) varieties. However, the mechanisms by which PGMS lines perceive changes in photoperiod and transmit those signals to elicit downstream effects are not well understood. In this study, we compared the transcriptomes from the leaves and anthers of carbon starved anther (csa), a PGMS line, to wild-type (WT) tissues under different photoperiods. Components of circadian clock in the leaves, including Circadian Clock-Associated 1 and Pseudo-Response Regulator (PRR95), played vital roles in sensing the photoperiod signals. Photoperiod signals were weakly transduced to anthers, where gene expression was mainly controlled by the CSA allele. CSA played a critical role in regulating sugar metabolism and cell wall synthesis in anthers under short-day conditions, and transcription of key genes inducing csa-directed sterility was upregulated under long-day (LD) conditions though not to WT levels, revealing a mechanism to explain the partial restoration of fertility in rice under LD conditions. Eight direct targets of CSA regulation were identified, all of which were genes involved in sugar metabolism and transport (cell wall invertases, SWEETs, and monosaccharide transporters) expressed only in reproductive tissues. Several hub genes coordinating the effects of CSA regulation were identified as critical elements determining WT male fertility and further analysis of these and related genes will reveal insights into how CSA coordinates sugar metabolism, cell wall biosynthesis, and photoperiod sensing in rice anther development.

UDP-glucose pyrophosphorylase: genome-wide identification, expression and functional analyses in Gossypium hirsutum

In this study, a total of 66 UDP-glucose pyrophosphorylase (UGP) (EC 2.7.7.9) genes were identified from the genomes of four cotton species, which are the members of Pfam glycosyltransferase family (PF01702) and catalyze the reaction between glucose-1-phosphate and UTP to produce UDPG. The analysis of evolutionary relationship, gene structure, and expression provides the basis for studies on function of UGP genes in cotton. The evolutionary tree and gene structure analysis revealed that the UGP gene family is evolutionarily conserved. Collinearity and Ka/Ks analysis indicated that amplification of UGP genes is due to repetitive crosstalk generating between new family genes, while being under strong selection pressure. The analysis of cis-acting elements exhibited that UGP genes play important role in cotton growth, development, abiotic and hormonal stresses. Six UGP genes that were highly expressed in cotton fiber at 15 DPA were screened by transcriptome data and qRT-PCR analysis. The addition of low concentrations of IAA and GA3 to ovule cultures revealed that energy efficiency promoted the development of ovules and fiber clusters, and qRT-PCR showed that expression of these six UGP genes was differentially increased. These results suggest that the UGP gene may play an important role in fiber development, and provides the opportunity to plant researchers to explore the mechanisms involve in fiber development in cotton.

Regulatory Networks of Flowering Genes in Angelica sinensis during Vernalization

Angelica sinensis is a low-temperature and long-day perennial herb that has been widely used for cardio-cerebrovascular diseases in recent years. In commercial cultivation, up to 40% of flowering decreases the officinal yield of roots and accumulation of bioactive compounds. Although the regulatory mechanism of flowering genes during the photoperiod has been revealed, the networks during vernalization have not been mapped. Here, transcriptomics profiles of A. sinensis with uncompleted (T1), completed (T2) and avoided vernalization (T3) were performed using RNA-seq, and genes expression was validated with qRT-PCR. A total of 61,241 isoforms were annotated on KEGG, KOG, Nr and Swiss-Prot databases; 4212 and 5301 differentially expressed genes (DEGs) were observed; and 151 and 155 genes involved in flowering were dug out at T2 vs. T1 and T3 vs. T1, respectively. According to functional annotation, 104 co-expressed genes were classified into six categories: FLC expression (22; e.g., VILs, FCA and FLK), sucrose metabolism (12; e.g., TPSs, SUS3 and SPSs), hormone response (18; e.g., GID1B, RAP2s and IAAs), circadian clock (2; i.e., ELF3 and COR27), downstream floral integrators and meristem identity (15; e.g., SOC1, AGL65 and SPLs) and cold response (35; e.g., PYLs, ERFs and CORs). The expression levels of candidate genes were almost consistent with FPKM values and changes in sugar and hormone contents. Based on their functions, four pathways that regulate flowering during vernalization were mapped, including the vernalization pathway, the autonomic pathway, the age pathway and the GA (hormone) pathway. This transcriptomic analysis provides new insights into the gene-regulatory networks of flowering in A. sinensis.

Starch Degradation and Sucrose Accumulation of Lily Bulbs after Cold Storage

Functional lilies are a group of edible lily cultivars with great potential for landscape application. Low-temperature storage can significantly improve their taste, but the knowledge of this process is largely unknown. In this study, we used the functional lilies 'Fly Shaohua' and 'Fly Tiancheng' as materials. Through physiological observation and transcriptome analysis during the bulbs' cold storage, it was found that the starch degradation and sucrose accumulation in bulbs contributed to taste improvement. After 60 d of cold storage, the sucrose accumulation was highest and the starch content was lower in the bulbs, suggesting this time-point was optimal for consumption. Accompanying the fluctuation of sucrose content during cold storage, the enzyme activities of sucrose phosphate synthase and sucrose synthase for sucrose synthesis were increased. Transcriptome analysis showed that many differentially expressed genes (DEGs) were involved in the starch and sucrose metabolism pathway, which might promote the conversion of starch to sucrose in bulbs. In addition, the DEGs involved in dormancy and stress response were also determined during cold storage, which might explain the decreased sucrose accumulation with extended storage time over 60 d due to the energy consumption for dormancy release. Taken together, our results indicated sucrose accumulation was a main factor in the taste improvement of lily bulbs after cold storage, which is attributable to the different gene expression of starch and sucrose metabolism pathways in this process.

An Updated Review on the Modulation of Carbon Partitioning and Allocation in Arbuscular Mycorrhizal Plants

Arbuscular mycorrhizal fungi (AMF) are obligate biotrophs that supply mineral nutrients to the host plant in exchange for carbon derived from photosynthesis. Sucrose is the end-product of photosynthesis and the main compound used by plants to translocate photosynthates to non-photosynthetic tissues. AMF alter carbon distribution in plants by modifying the expression and activity of key enzymes of sucrose biosynthesis, transport, and/or catabolism. Since sucrose is essential for the maintenance of all metabolic and physiological processes, the modifications addressed by AMF can significantly affect plant development and stress responses. AMF also modulate plant lipid biosynthesis to acquire storage reserves, generate biomass, and fulfill its life cycle. In this review we address the most relevant aspects of the influence of AMF on sucrose and lipid metabolism in plants, including its effects on sucrose biosynthesis both in photosynthetic and heterotrophic tissues, and the influence of sucrose on lipid biosynthesis in the context of the symbiosis. We present a hypothetical model of carbon partitioning between plants and AMF in which the coordinated action of sucrose biosynthesis, transport, and catabolism plays a role in the generation of hexose gradients to supply carbon to AMF, and to control the amount of carbon assigned to the fungus.

The impact of carbon source on cell growth and the production of bioactive compounds in cell suspensions of Hancornia speciosa Gomes

Belonging to the Brazilian flora, the species Hancornia speciosa (Gomes), known as mangabeira, has bioactive compounds of interest, such as flavonoids, xanthones, and proanthocyanidins. The objective of this study was to determine how the supplementation of sugars in culture medium affects the osmotic potential of the medium, as well as its influence on cell growth and on the concentration of phenolic compounds. For this purpose, after 90 days of subculture, 20 mL aliquots of the cultures were added to flasks containing 20 mL of medium with different sugars (glucose, fructose, sucrose, mannitol, and sorbitol) under a 16-h photoperiod with a spectral range between 400 and 700 nm of photosynthetically active radiation (45-55 μmol m-2 s-1) in a shaker at 110 rpm. After 30 days, the pH, electrical conductivity, osmotic potential, biomass accumulation, and concentrations of phenolic compounds were evaluated. Regardless of their concentration in the medium, the sugars sorbitol and mannitol provided more unfavorable conditions for water absorption at the cellular level, reducing the water potential of the medium. Sucrose favored greater water absorption and biomass accumulation. Among the various sugar concentrations, 3% (30 g/L) sucrose or glucose improved the accumulation of fresh and dry cell weight and the production of polyphenols such as chlorogenic acid, epicatechin, rosmarinic acid, hesperidin, rutin, and quercetin. In addition, they resulted in a higher osmotic potential of the medium and larger cells than other carbon sources. Despite the differences in cell size, no culture conditions compromised cell survival.

QTL Mapping and GWAS Reveal the Genetic Mechanism Controlling Soluble Solids Content in Brassica napus Shoots

Oilseed-vegetable-dual-purpose (OVDP) rapeseed can effectively alleviate the land contradiction between crops and it supplements vegetable supplies in winter or spring. The soluble solids content (SSC) is an important index that is used to evaluate the quality and sugar content of fruits and vegetables. However, the genetic architecture underlying the SSC in Brassica napus shoots is still unclear. Here, quantitative trait loci (QTLs) for the SSC in B. napus shoots were investigated by performing linkage mapping using a recombinant inbred line population containing 189 lines. A germplasm set comprising 302 accessions was also used to conduct a genome-wide association study (GWAS). The QTL mapping revealed six QTLs located on chromosomes A01, A04, A08, and A09 in two experiments. Among them, two major QTLs, qSSC/21GY.A04-1 and qSSC/21NJ.A08-1, accounted for 12.92% and 10.18% of the phenotypic variance, respectively. In addition, eight single-nucleotide polymorphisms with phenotypic variances between 5.62% and 10.18% were identified by the GWAS method. However, no locus was simultaneously identified by QTL mapping and GWAS. We identified AH174 (7.55 °Brix and 7.9 °Brix), L166 (8.9 °Brix and 8.38 °Brix), and L380 (8.9 °Brix and 7.74 °Brix) accessions can be used as superior parents. These results provide valuable information that increases our understanding of the genetic control of SSC and will facilitate the breeding of high-SSC B. napus shoots.

Finding the C4 sweet spot: cellular compartmentation of carbohydrate metabolism in C4 photosynthesis

The two-cell type C4 photosynthetic pathway requires both anatomical and biochemical specialization to achieve a functional CO2-concentrating mechanism. While a great deal of research has been done on Kranz anatomy and cell-specific expression and activity of enzymes in the C4 pathway, less attention has been paid to partitioning of carbohydrate synthesis between the cell types of C4 leaves. As early as the 1970s it became apparent that, in the small number of species examined at the time, sucrose was predominantly synthesized in the mesophyll cells and starch in the bundle sheath cells. Here we discuss how this partitioning is achieved in C4 plants and explore whether this is a consequence of C4 metabolism or indeed a requirement for its evolution and efficient operation.

The Natural Antisense Transcript DONE40 Derived from the lncRNA ENOD40 Locus Interacts with SET Domain Protein ASHR3 During Inception of Symbiosis in Arachis hypogaea

The long noncoding RNA ENOD40 is required for cortical cell division during root nodule symbiosis (RNS) of legumes, though it is not essential for actinorhizal RNS. Our objective was to understand whether ENOD40 was required for aeschynomenoid nodule formation in Arachis hypogaea. AhENOD40 express from chromosome 5 (chr5) (AhENOD40-1) and chr15 (AhENOD40-2) during symbiosis, and RNA interference of these transcripts drastically affected nodulation, indicating the importance of ENOD40 in A. hypogaea. Furthermore, we demonstrated several distinct characteristics of ENOD40. (i) Natural antisense transcript (NAT) of ENOD40 was detected from the AhENOD40-1 locus (designated as NAT-AhDONE40). (ii) Both AhENOD40-1 and AhENOD40-2 had two exons, whereas NAT-AhDONE40 was monoexonic. Reverse-transcription quantitative PCR analysis indicated both sense and antisense transcripts to be present in both cytoplasm and nucleus, and their expression increased with the progress of symbiosis. (iii) RNA pull-down from whole cell extracts of infected roots at 4 days postinfection indicated NAT-AhDONE40 to interact with the SET (Su(var)3-9, enhancer of Zeste and Trithorax) domain containing absent small homeotic disc (ASH) family protein AhASHR3 and this interaction was further validated using RNA immunoprecipitation and electrophoretic mobility shift assay. (iv) Chromatin immunoprecipitation assays indicate deposition of ASHR3-specific histone marks H3K36me3 and H3K4me3 in both of the ENOD40 loci during the progress of symbiosis. ASHR3 is known for its role in optimizing cell proliferation and reprogramming. Because both ASHR3 and ENOD40 from legumes cluster away from those in actinorhizal plants and other nonlegumes in phylogenetic distance trees, we hypothesize that the interaction of DONE40 with ASHR3 could have evolved for adapting the nodule organogenesis program for legumes.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Sucrose Metabolism and Transport in Grapevines, with Emphasis on Berries and Leaves, and Insights Gained from a Cross-Species Comparison

In grapevines, as in other plants, sucrose and its constituents glucose and fructose are fundamentally important and carry out a multitude of roles. The aims of this review are three-fold. First, to provide a summary of the metabolism and transport of sucrose in grapevines, together with new insights and interpretations. Second, to stress the importance of considering the compartmentation of metabolism. Third, to outline the key role of acid invertase in osmoregulation associated with sucrose metabolism and transport in plants.

Key Regulators of Sucrose Metabolism Identified through Comprehensive Comparative Transcriptome Analysis in Peanuts

Sucrose content is a crucial indicator of quality and flavor in peanut seed, and there is a lack of clarity on the molecular basis of sucrose metabolism in peanut seed. In this context, we performed a comprehensive comparative transcriptome study on the samples collected at seven seed development stages between a high-sucrose content variety (ICG 12625) and a low-sucrose content variety (Zhonghua 10). The transcriptome analysis identified a total of 8334 genes exhibiting significantly different abundances between the high- and low-sucrose varieties. We identified 28 differentially expressed genes (DEGs) involved in sucrose metabolism in peanut and 12 of these encoded sugars will eventually be exported transporters (SWEETs). The remaining 16 genes encoded enzymes, such as cell wall invertase (CWIN), vacuolar invertase (VIN), cytoplasmic invertase (CIN), cytosolic fructose-bisphosphate aldolase (FBA), cytosolic fructose-1,6-bisphosphate phosphatase (FBP), sucrose synthase (SUS), cytosolic phosphoglucose isomerase (PGI), hexokinase (HK), and sucrose-phosphate phosphatase (SPP). The weighted gene co-expression network analysis (WGCNA) identified seven genes encoding key enzymes (CIN, FBA, FBP, HK, and SPP), three SWEET genes, and 90 transcription factors (TFs) showing a high correlation with sucrose content. Furthermore, upon validation, six of these genes were successfully verified as exhibiting higher expression in high-sucrose recombinant inbred lines (RILs). Our study suggested the key roles of the high expression of SWEETs and enzymes in sucrose synthesis making the genotype ICG 12625 sucrose-rich. This study also provided insights into the molecular basis of sucrose metabolism during seed development and facilitated exploring key candidate genes and molecular breeding for sucrose content in peanuts.

Transcriptome analysis of Sonneratia caseolaris seedlings under chilling stress

Sonneratia caseolaris is a native mangrove species found in China. It is fast growing and highly adaptable for mangrove afforestation, but suffered great damage by chilling event once introduced to high latitude area. To understand the response mechanisms under chilling stress, physiological and transcriptomic analyses were conducted. The relative electrolyte conductivity, malondialdehyde (MDA) content, soluble sugar content and soluble protein content increased significantly under chilling stress. This indicated that S. caseolaris suffered great damage and increased the levels of osmoprotectants in response to the chilling stress. Gene expression comparison analysis of S. caseolaris leaves after 6 h of chilling stress was performed at the transcriptional scale using RNA-Seq. A total of 168,473 unigenes and 3,706 differentially expressed genes (DEGs) were identified. GO and KEGG enrichment analyses showed that the DEGs were mainly involved in carbohydrate metabolism, antioxidant enzyme, plant hormone signal transduction, and transcription factors (TFs). Sixteen genes associated with carbohydrate metabolism, antioxidant enzyme, phytohormones and TFs were selected for qRT-PCR verification, and they indicated that the transcriptome data were reliable. Our work provided a comprehensive review of the chilling response of S. caseolaris at both physiological and transcriptomic levels, which will prove useful for further studies on stress-responses in mangrove plants.

The Associated With Carbon Conversion Rate and Source-Sink Enzyme Activity in Tomato Fruit Subjected to Water Stress and Potassium Application

Carbon metabolism in higher plants is a basic physiological metabolism, and carbon allocation and conversion require the activity of various enzymes in metabolic processes that alter the content and overall composition of sugars in the sink organ. However, it is not known how various enzymes affect carbon metabolism when tomato plants are subjected to water stress or treated with potassium. Although the process of carbon metabolism is very complex, we used the carbon conversion rate to compare and analyze the enzyme activities related to sugar metabolism and find out which carbon conversion rate are the most important. Results showed that water stress and potassium increased carbon import flux in the fruit, which was beneficial to carbon accumulation. Water deficit increased the activity of sucrose synthase (SuSy) and starch phosphorylase (SP) and decreased the activity of sucrose phosphate synthase (SPS) and adenosine diphosphate glucose pyrophosphorylase (AGPase) in the source. Water stress increased the activity of acid invertase (AI), SuSy and SP but decreased the activity of AGPase in the sink. Potassium modified the balance of enzymes active in sugar and starch metabolism by increasing the activity of AI, SuSy, SPS and SP and significantly decreasing the activity of AGPase, resulting in increase of hexose. Canonical correlational analysis revealed that the carbon conversion rate was mainly affected by the relative rate of conversion of sucrose to fructose and glucose [p1(t)] and glucose to starch [p5m(t)]. SuSy and AGPase had the greatest effect on enzyme activity in the fruit; respectively regulated p 1(t) and p 5m(t).

Molecular and Hormonal Mechanisms Regulating Fleshy Fruit Ripening

This article focuses on the molecular and hormonal mechanisms underlying the control of fleshy fruit ripening and quality. Recent research on tomato shows that ethylene, acting through transcription factors, is responsible for the initiation of tomato ripening. Several other hormones, including abscisic acid (ABA), jasmonic acid (JA) and brassinosteroids (BR), promote ripening by upregulating ethylene biosynthesis genes in different fruits. Changes to histone marks and DNA methylation are associated with the activation of ripening genes and are necessary for ripening initiation. Light, detected by different photoreceptors and operating through ELONGATED HYPOCOTYL 5(HY5), also modulates ripening. Re-evaluation of the roles of 'master regulators' indicates that MADS-RIN, NAC-NOR, Nor-like1 and other MADS and NAC genes, together with ethylene, promote the full expression of genes required for further ethylene synthesis and change in colour, flavour, texture and progression of ripening. Several different types of non-coding RNAs are involved in regulating expression of ripening genes, but further clarification of their diverse mechanisms of action is required. We discuss a model that integrates the main hormonal and genetic regulatory interactions governing the ripening of tomato fruit and consider variations in ripening regulatory circuits that operate in other fruits.

Multi-Wall Carbon Nanotubes Promote the Growth of Maize (Zea mays) by Regulating Carbon and Nitrogen Metabolism in Leaves

Previous studies have suggested that multiwalled carbon nanotubes (MWCNTs) promote plant growth; however, the mechanism is yet to be fully understood. In this study, the effects of MWCNTs (20, 100, and 500 mg/L) on the carbon (C) and nitrogen (N) metabolism in maize were studied to explore the molecular mechanism of the action of MWCNTs on plants. The results showed that 100 mg/L MWCNTs increased the shoot fresh and dry weight, root fresh weight, and seedling length while other doses showed no significant effects. Further studies showed that 100 mg/L MWCNTs increased the chlorophyll content, transpiration rate, stomatal conductance, and intercellular CO₂ concentration, by 50.6%, 60.8%, 47.2%, and 32.1%, respectively. Activities of key enzymes including sucrose synthase (SS), sucrose phosphate synthase (SPS) and phosphoenolpyruvate carboxylase (PEPC) that are involved in the carbon metabolism, and nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthetase (GOGAT) that are involved in N metabolism, were all upregulated by 100 mg/L MWCNTs, which contributed to the increase of the accumulation of carbohydrates (sugar and starch), soluble protein, and N in plants. These findings suggest that MWCNTs can improve plant growth by regulating the key enzymes involved in C and N metabolism thereby enhancing the carbohydrate production and the use of N and improving plant growth. This study provides significant insights into the molecular mechanism of the positive effects of MWCNTs on plants and provide a basis for the agricultural application of MWCNTs.

A Palette of Minimally Tagged Sucrose Analogues for Real-Time Raman Imaging of Intracellular Plant Metabolism

Sucrose is the main saccharide used for long-distance transport in plants and plays an essential role in energy metabolism; however, there are no analogues for real-time imaging in live cells. We have optimised a synthetic approach to prepare sucrose analogues including very small (≈50 Da or less) Raman tags in the fructose moiety. Spectroscopic analysis identified the alkyne-tagged compound 6 as a sucrose analogue recognised by endogenous transporters in live cells and with higher Raman intensity than other sucrose derivatives. Herein, we demonstrate the application of compound 6 as the first optical probe to visualise real-time uptake and intracellular localisation of sucrose in live plant cells using Raman microscopy.

A Palette of Minimally Tagged Sucrose Analogues for Real-Time Raman Imaging of Intracellular Plant Metabolism

Sucrose is the main saccharide used for long-distance transport in plants and plays an essential role in energy metabolism; however, there are no analogues for real-time imaging in live cells. We have optimised a synthetic approach to prepare sucrose analogues including very small (≈50 Da or less) Raman tags in the fructose moiety. Spectroscopic analysis identified the alkyne-tagged compound 6 as a sucrose analogue recognised by endogenous transporters in live cells and with higher Raman intensity than other sucrose derivatives. Herein, we demonstrate the application of compound 6 as the first optical probe to visualise real-time uptake and intracellular localisation of sucrose in live plant cells using Raman microscopy.

Transcriptomic and metabolomic analyses of non-structural carbohydrates in red maple leaves

Plant sugars serve to balance nutrition, regulate development, and respond to biotic and abiotic stresses, whereas non-structural carbohydrates (NSCs) are essential energy sources that facilitate plant growth, metabolism, and environmental adaptation. To better elucidate the mechanisms of NSCs in red maple, ultrahigh-performance liquid chromatograph Q extractive mass spectrometry (UHPLC-QE-MS) and high-throughput RNA-sequencing were performed on green, red, and yellow leaves from a selected red maple mutant. In green leaves, the fructose phosphorylation process exhibited greater flux. In yellow leaves, sucrose and starch had a stronger capacity for synthesis and degradation, whereas in red leaves, there was a greater accumulation of trehalose and manninotriose. ArTPS5 positively regulated amylose, which was negatively regulated by ArFBP2, whereas ArFRK2 and ArFBP13 played a positive role in the biosynthesis of Sucrose-6P. Sucrose-6P also regulated anthocyanins and abscisic acid in red maple by affecting transcription factors. The results of this paper can assist with the control and optimization of the biosynthesis of NSCs in red maple, which may ultimately provide the foundation for influencing sugar production in Acer.

Reddy V, Song L, Gao H, Cao B. Cloning and Characterization of Three Sugar Metabolism Genes (LBGAE, LBGALA, and LBMS) Regulated in Response to Elevated CO2 in Goji Berry (Lycium barbarum L.)

The composition and content of sugar play a pivotal role in goji berry (Lycium barbarum L.) fruits, determining fruit quality. Long-term exposure of goji berry to elevated CO₂ (eCO₂) was frequently demonstrated to reduce sugar content and secondary metabolites. In order to understand the regulatory mechanisms and improve the quality of fruit in the changing climate, it is essential to characterize sugar metabolism genes that respond to eCO₂. The objectives of this study were to clone full-length cDNA of three sugar metabolism genes—LBGAE (Lycium barbarum UDP-glucuronate 4-epimerase), LBGALA (Lycium barbarum alpha-galactosidase), and LBMS (Lycium barbarum malate synthase)—that were previously identified responding to eCO₂, and to analyze sequence characteristics and expression regulation patterns. Sugar metabolism enzymes regulated by these genes were also estimated along with various carbohydrates from goji berry fruits grown under ambient (400 μmol mol⁻¹) and elevated (700 μmol mol⁻¹) CO₂ for 90 and 120 days. Homology-based sequence analysis revealed that the protein-contained functional domains are similar to sugar transport regulation and had a high sequence homology with other Solanaceae species. The sucrose metabolism-related enzyme’s activity varied significantly from ambient to eCO₂ in 90-day and 120-day samples along with sugars. This study provides fundamental information on sugar metabolism genes to eCO₂ in goji berry to enhance fruit quality to climate change.

Physiological and Transcripts Analyses Reveal the Mechanism by Which Melatonin Alleviates Heat Stress in Chrysanthemum Seedlings

Heat stress limits the growth and development of chrysanthemum seedlings. Although melatonin (MT) has been linked to the heat stress response in plants, research on the underlying molecular mechanisms is scarce. In this study, the regulatory networks of MT on heat stress in chrysanthemum seedlings were explored. Physiological measurements suggested that MT not only reduced malondialdehyde accumulation, hydrogen peroxide content, and superoxide anion free radical generation rate, but also significantly promoted osmotic regulation substance synthesis (proline and soluble protein), antioxidant accumulation (GSH and AsA), and the antioxidant enzyme activities (SOD, POD, CAT, and APX) in chrysanthemum leaves under heat stress. Furthermore, MT increased the fresh weight, dry weight, chlorophyll content, photosynthesis rate, and gas exchange indexes. Further, RNA-seq results revealed 33,497 and 36,740 differentially expressed genes in the S/Con and SMT/ConMT comparisons, respectively. The differences in the comparisons revealed that MT regulated heat shock transcription factors (HSFs) and heat shock proteins (HSPs), and the genes involved in Ca²⁺ signal transduction (CNGCs and CAM/CMLs), starch and sucrose metabolism (EDGL, BGLU, SuS, and SPS), hormone (PP2Cs, AUX/IAAs, EBFs, and MYC2), chlorophyll metabolism (HEMA and PORA), flavonoid biosynthesis (CHS, DFR, and FNS), and carotenoid biosynthesis (DXPS, GGDP, and PSY). MT effectively improved chrysanthemum seedling heat-resistance. Our study, thus, provides novel evidence of a gene network regulated by MT under heat stress.

Physiological Changes of Bamboo (Fargesia yunnanensis) Shoots During Storage and the Related Cold Storage Mechanisms

The mechanisms for physiological senescence in bamboo shoots after harvest remain unclear. This study investigated physiological changes in Fargesia yunnanensis shoots during storage at different temperatures. The relationship between morphological and physiological changes in bamboo shoots during storage was also analyzed. The results show that cold storage can reduce weight loss, browning, respiration rates, and sugar degradation in bamboo shoots; decrease related enzymatic activities; and inhibit the increase in lignin and cellulose content. The quality of bamboo shoots declines more during the first 3d after harvesting than it does during subsequent periods. The increase in the degree of lignification and fibrosis is the main reason for senescence and for the decline in quality of bamboo shoots after harvest. The bamboo shoots under RT conditions began browning during the third 3d of storage, with a browning rate of 688gkg^-1 even in the upper parts; the increase in shoot browning degrees significantly decreased the quality. Low temperatures had better inhibitory effects on browning than they did on lignification and fibrosis. Nonstructural carbohydrates in bamboo shoots are degraded and flow into sheath and shoot respiration, phenols, and shoot fibrosis and lignification at room temperature, but only flow into sheath respiration, shoot fibrosis, and lignification at cold temperature. Soluble protein and free amino acids are primarily distributed into shoot and sheath respiration and into phenols at room temperature, but that process is well inhibited at cold temperature. Bamboo shoots, once removed from cold storage, should be consumed rapidly because enzyme activity recovers quickly. This research provides new theoretical information on the preservation of bamboo shoots.

Physiological Profiling of Embryos and Dormant Seeds in Two Arabidopsis Accessions Reveals a Metabolic Switch in Carbon Reserve Accumulation

In flowering plants, sugars act as carbon sources providing energy for developing embryos and seeds. Although most studies focus on carbon metabolism in whole seeds, knowledge about how particular sugars contribute to the developmental transitions during embryogenesis is scarce. To develop a quantitative understanding of how carbon composition changes during embryo development, and to determine how sugar status contributes to final seed or embryo size, we performed metabolic profiling of hand-dissected embryos at late torpedo and mature stages, and dormant seeds, in two Arabidopsis thaliana accessions with medium [Columbia-0 (Col-0)] and large [Burren-0 (Bur-0)] seed sizes, respectively. Our results show that, in both accessions, metabolite profiles of embryos largely differ from those of dormant seeds. We found that developmental transitions from torpedo to mature embryos, and further to dormant seeds, are associated with major metabolic switches in carbon reserve accumulation. While glucose, sucrose, and starch predominantly accumulated during seed dormancy, fructose levels were strongly elevated in mature embryos. Interestingly, Bur-0 seeds contain larger mature embryos than Col-0 seeds. Fructose and starch were accumulated to significantly higher levels in mature Bur-0 than Col-0 embryos, suggesting that they contribute to the enlarged mature Bur-0 embryos. Furthermore, we found that Bur-0 embryos accumulated a higher level of sucrose compared to hexose sugars and that changes in sucrose metabolism are mediated by sucrose synthase (SUS), with SUS genes acting non-redundantly, and in a tissue-specific manner to utilize sucrose during late embryogenesis.

Molecular cloning and expression analysis of sucrose phosphate synthase genes in cassava (Manihot esculenta Crantz)

Sucrose phosphate synthase (SPS), a key rate-limiting enzyme in the sucrose biosynthesis pathway in plants, is encoded by a multi-gene family. Until recently, the identification and characterization of the SPS gene family have been performed for dozens of plant species; however, few studies have involved a comprehensive analysis of the SPS family members in tropical crops, such as cassava (Manihot esculenta Crantz). In the current study, five SPS genes (MeSPS1, MeSPS2, MeSPS3, MeSPS4, and MeSPS5) were isolated from cassava, and their sequence characteristics were comprehensively characterized. These MeSPS genes were found distributed on five chromosomes (Chr2, Chr14, Chr15, Chr16, and Chr18). Phylogenetic analysis showed that the MeSPS protein sequences were clustered into three families, together with other SPS sequences from both dicot and monocot species (families A, B, and C). The spatio-temporal expression pattern analysis of MeSPS genes showed a tissue-specific and partially overlapping expression pattern, with the genes mainly expressed in source tissues during cassava growth and development. Correlation analysis revealed that the expression of MeSPS genes correlated positively with root starch content, indicating that the expression of MeSPS genes might accelerate the rate of starch accumulation in the roots of cassava plants.

Multi-omics analysis of cellular pathways involved in different rapid growth stages of moso bamboo

Moso bamboo (Phyllostachys edulis (Carriere) J. Houzeau) is a rapidly growing grass of industrial and ecological importance. However, the molecular mechanisms of its remarkable growth are not well understood. In this study, we investigated the early-stage growth of moso bamboo shoots and defined three different growth stages based on histological and biochemical analyses, namely, starting of cell division (SD), rapid division (RD) and rapid elongation (RE). Further analyses on potentially relevant cellular pathways in these growth stages using multi-omics approaches such as transcriptomics and proteomics revealed the involvement of multiple cellular pathways, including DNA replication, repair and ribosome biogenesis. A total of 8045 differentially expressed genes (DEGs) and 1053 differentially expressed proteins (DEPs) were identified in our analyses. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses of detected DEGs identified several key biological pathways such as phytohormone metabolism, signal transduction, cell wall development and carbohydrate metabolism. The comparative analysis of proteins displayed that a total of 213 DEPs corresponded with DEGs and 3 significant expression profiles that could be promoting the fast growth of bamboo internodes. Moreover, protein-protein interaction network prediction analysis is suggestive of the involvement of five major proteins of signal transduction, DNA synthesis and RNA transcription, and may act as key elements responsible for the rapid shoot growth. Our work exploits multi-omics and bioinformatic approaches to unfurl the complexity of molecular networks involved in the rapid growth of moso bamboo and opens up questions related to the interactions between the functions played by individual molecular pathway.

Transcriptome Analyses and Antioxidant Activity Profiling Reveal the Role of a Lignin-Derived Biostimulant Seed Treatment in Enhancing Heat Stress Tolerance in Soybean

Soybean (Glycine max Merr.) is a worldwide important legume crop, whose growth and yield are negatively affected by heat stress at germination time. Here, we tested the role of a biostimulant based on lignin derivatives, plant-derived amino acids, and molybdenum in enhancing soybean heat stress tolerance when applied on seeds. After treatment with the biostimulant at 35 °C, the seed biometric parameters were positively influenced after 24 h, meanwhile, germination percentage was increased after 72 h (+10%). RNA-Seq analyses revealed a modulation of 879 genes (51 upregulated and 828 downregulated) in biostimulant-treated seeds as compared with the control, at 24 h after incubation at 35 °C. Surprisingly, more than 33% of upregulated genes encoded for ribosomal RNA (rRNA) methyltransferases and proteins involved in the ribosome assembly, acting in a specific protein network. Conversely, the downregulated genes were involved in stress response, hormone signaling, and primary metabolism. Finally, from a biochemical point of view, the dramatic H₂O₂ reduction 40%) correlated to a strong increase in non-protein thiols (+150%), suggested a lower oxidative stress level in biostimulant-treated seeds, at 24 h after incubation at 35 °C. Our results provide insights on the biostimulant mechanism of action and on its application for seed treatments to improve heat stress tolerance during germination.

Transactivation of Sus1 and Sus2 by Opaque2 is an essential supplement to sucrose synthase-mediated endosperm filling in maize

The endosperm-specific transcription factor Opaque2 (O2) acts as a central regulator for endosperm filling, but its functions have not been fully defined. Regular o2 mutants exhibit a non-vitreous phenotype, so we used its vitreous variety Quality Protein Maize to create EMS-mutagenesis mutants for screening o2 enhancers (oen). A mutant (oen1) restored non-vitreousness and produced a large cavity in the seed due to severely depleted endosperm filling. When oen1 was introgressed into inbred W64A with a normal O2 gene, the seeds appeared vitreous but had a shrunken crown. oen1 was determined to encode Shrunken1 (Sh1), a sucrose synthase (SUS, EC 2.4.1.13). Maize contains three SUS-encoding genes (Sh1, Sus1, and Sus2) with Sh1 contributing predominantly to the endosperm. We determined SUS activity and found a major and minor reduction in oen1 and o2, respectively. In o2;oen1-1, SUS activity was further decreased. We found all Sus gene promoters contain at least one O2 binding element that can be specifically recognized and be transactivated by O2. Sus1 and Sus2 promoters had a much stronger O2 transactivation than Sh1, consistent with their transcript reduction in o2 endosperm. Although sus1 and sus2 alone or in combination had no perceptible phenotype, either of them could dramatically enhance seed opacity and cavity in sh1, indicating that transactivation of Sus1 and Sus2 by O2 supplements SUS-mediated endosperm filling in maize. Our findings demonstrate that O2 transcriptionally regulates the metabolic source entry for protein and starch synthesis during endosperm filling.

Sucrose phosphate synthase (SPS), sucrose synthase (SUS) and their products in the leaves of Miscanthus × giganteus and Zea mays at low temperature

The changes in the expression of key sugar metabolism enzymes (SPS and SUS), sucrose content and arrangement of chloroplast starch may play a significant role in the cold response in M. giganteus and maize plants. To understand the mechanism of the chilling-response of two closely-related C₄ plants, we investigated the changes in the expression of sucrose phosphate synthase (SPS) and sucrose synthase (SUS) as well as changes in their potential products: sucrose, cellulose and starch in the leaves of Miscanthus × giganteus and Zea mays. Low temperature (12-14 °C) increased SPS content in Miscanthus (MG) and chilling-sensitive maize line (Zm-S), but not in chilling-tolerant one (Zm-T). In Zm-S line, chilling also caused the higher intensity of labelling of SPS in the cytoplasm of mesophyll cells, as demonstrated by electron microscopy. SUS labelling was also increased by cold stress only in MG plants what was observed in the secondary wall between mesophyll and bundle sheath cells, as well as in the vacuoles of companion cells. Cold led to a marked increase in total starch grain area in the chloroplasts of Zm-S line. In turn, Fourier transform infrared spectroscopy (FTIR) showed a slight shift in the cellulose band position, which may indicate the formation of more compact cellulose arrangement in Zm-T maize line. In conclusion, this work presents new findings supporting diversified cold-response, not only between two C₄ plant species but also within one species of maize.

SUGAR Model-Assisted Analysis of Carbon Allocation and Transformation in Tomato Fruit Under Different Water Along With Potassium Conditions

Carbohydrate concentrations in fruit are closely related to the availability of water and mineral nutrients. Water stress and minerals alter the assimilation, operation, and distribution of carbohydrates, thereby affecting the fruit quality. The SUGAR model was used to investigate the carbon balance in tomato fruit during different growth stages when available water was varied and potassium added. Further, we quantitatively studied the distribution of photoassimilates such as structural carbohydrates, soluble sugars, and starch in fruit and evaluated their response to water and potassium supply. The results revealed that the carbon allocation and transformation dynamically changed during the all growth stages; in fact, variation in carbon content showed similar trends for different water along with potassium treatments, carbon allocation during the early development stages was mainly to starch and structural carbon compounds. The relative rate of carbon conversion of soluble sugars to structural carbon compounds (k 3) and of soluble sugars to starch (k 5m ) peaked during the initial stage and then dropped during fruit growth and development stages. Carbon was primarily allocated as soluble sugars and starch was converted to soluble sugars at fruit maturation. k 3(t) and k 5m (t) approached zero at the end of the growth stage, mainly due to sugar accumulation. Potassium application can significantly raise carbon flows imported (C supply ) from the phloem into the fruit and thus increased carbon allocation to soluble sugars over the entire growth period. Potassium addition during the fruit maturation stage decreased the content of starch and other carbon compounds. Water deficit regulated carbon allocation and increased soluble sugar content but reduced structural carbon content, thereby improving fruit quality.

Mapping and characterization of major QTL for spike traits in common wheat

The spike traits of wheat can directly affect yield. F₂ and F_2:3 lines derived from the cross of the multi-spikelet female 10-A and the uni-spikelet male BE89 were used to detect QTLs for spike length (SL), total spikelet number per spike (TSS), kernel number per spike (KNS) and thousand-kernel weight (TKW) in four different environments. A total of 1098 SNP and 5 SSR were used to construct genetic map of 2398.1 cM with the average distance of 2.2 cM between markers. A total of 11 QTLs were identified for spike traits, including three QTLs for SL, five QTLs for TSS, two QTLs for KNS and one QTL for TKW. The QTLs mapped to chromosomes 2D, 4A, 6A, 7A and 7B explained 8.2-37.8% of the phenotypic variation in single environment. The major QTL confidence interval with distance of 0.5 cM was located on chromosome 4A and detected in multiple environments, which can explain more than 30% of the phenotypic variation for SL, TSS and KNS. Combining IWGSC RefSeq v1.0 and RNA-seq data for 10-A and BE89, we identified 16 genes expressed on spike or grain in four QTL regions. These findings provide insights into improving wheat yield through increasing spikletes in wheat, particularly through the use of the multi-spikelet female 10-A for breeding.

Co-crystal Structure of Thermosynechococcus elongatus Sucrose Phosphate Synthase With UDP and Sucrose-6-Phosphate Provides Insight Into Its Mechanism of Action Involving an Oxocarbenium Ion and the Glycosidic Bond

In green species, sucrose can help antagonize abiotic stress. Sucrose phosphate synthase (SPS) is a well-known rate-limiting enzyme in the synthesis of sucrose. To date, however, there is no known crystal structure of SPS from plant or cyanobacteria. In this study, we report the first co-crystal structure of SPS from Thermosynechococcus elongatus with UDP and sucrose-6-phosphate (S6P). Within the catalytic site, the side chains of His158 and Glu331, along with two phosphate groups from UDP, form hydrogen bonds with the four hydroxyl groups of the glucose moiety in S6P. This association causes these four hydroxyl groups to become partially negatively charged, thus promoting formation of the C1 oxocarbenium ion. Breakage of the hydrogen bond between His158 and one of the hydroxyl groups may trigger covalent bond formation between the C1 oxocarbenium ion and the C2 hydroxyl of fructose-6-phosphate. Consistent with our structural model, we observed that two SPS mutants, H158A and E331A, lost all catalytic activity. Moreover, electron density of residues from two loops (loop1 and loop2) in the SPS A-domain was not observed, suggest their dynamic nature. B-factor analysis and molecular dynamics stimulations of the full-length enzyme and A-domain indicate that both loops are crucial for binding and release of substrate and product. In addition, temperature gradient analysis shows that SPS exhibits its highest activity at 70°C, suggesting that this enzyme has the potential of being used in industrial production of S6P.

Comparative transcriptome analysis of two contrasting wolfberry genotypes during fruit development and ripening and characterization of the LrMYB1 transcription factor that regulates flavonoid biosynthesis

Background

Lycium barbarum and L. ruthenicum have been used as traditional medicinal plants in China and other Asian counties for centuries. However, the molecular mechanisms underlying fruit development and ripening, as well as the associated production of medicinal and nutritional components, have been little explored in these two species.

Results

A competitive transcriptome analysis was performed to identify the regulators and pathways involved in the fruit ripening of red wolfberry (L. barbarum) and black wolfberry (L. ruthenicum) using an Illumina sequencing platform. In total, 155,606 genes and 194,385 genes were detected in red wolfberry (RF) and black wolfberry (BF), respectively. Of them, 20,335, 24,469, and 21,056 genes were differentially expressed at three different developmental stages in BF and RF. Functional categorization of the differentially expressed genes revealed that phenylpropanoid biosynthesis, flavonoid biosynthesis, anthocyanin biosynthesis, and sugar metabolism were the most differentially regulated processes during fruit development and ripening in the RF and BF. Furthermore, we also identified 38 MYB transcription factor-encoding genes that were differentially expressed during black wolfberry fruit development. Overexpression of LrMYB1 resulted in the activation of structural genes for flavonoid biosynthesis and led to an increase in flavonoid content, suggesting that the candidate genes identified in this RNA-seq analysis are credible and might offer important utility.

Conclusion

This study provides novel insights into the molecular mechanism of Lycium fruit development and ripening and will be of value to novel gene discovery and functional genomic studies.

Magnesium Fertilization Improves Crop Yield in Most Production Systems: A Meta-Analysis

Magnesium deficiency is a frequently occurring limiting factor for crop production due to low levels of exchangeable Mg (ex-Mg) in acidic soil, which negatively affects sustainability of agriculture development. How Mg fertilization affects crop yield and subsequent physiological outcomes in different crop species, as well as agronomic efficiencies of Mg fertilizers, under varying soil conditions remain particular interesting questions to be addressed. A meta-analysis was performed with 570 paired observations retrieved from 99 field research articles to compare effects of Mg fertilization on crop production and corresponding agronomic efficiencies in different production systems under varying soil conditions. The mean value of yield increase and agronomic efficiency derived from Mg application was 8.5% and 34.4 kg kg-1 respectively, when combining all yield measurements together, regardless of the crop type, soil condition, and other factors. Under severe Mg deficiency (ex-Mg < 60 mg kg-1), yield increased up to 9.4%, nearly two folds of yield gain (4.9%) in the soil containing more than 120 mg kg-1 ex-Mg. The effects of Mg fertilization on yield was 11.3% when soil pH was lower than 6.5. The agronomic efficiency of Mg fertilizers was negatively correlated with application levels of Mg, with 38.3 kg kg-1 at lower MgO levels (0-50 kg ha-1) and 32.6 kg kg-1 at higher MgO levels (50-100 kg ha-1). Clear interactions existed between soil ex-Mg, pH, and types and amount of Mg fertilizers in terms of crop yield increase. With Mg supplementation, Mg accumulation in the leaf tissues increased by 34.3% on average; and concentrations of sugar in edible organs were 5.5% higher compared to non-Mg supplemented treatments. Our analysis corroborated that Mg fertilization enhances crop performance by improving yield or resulting in favorable physiological outcomes, providing great potentials for integrated Mg management for higher crop yield and quality.

The evolutionary history of the sucrose synthase gene family in higher plants

BACKGROUND

Sucrose synthase (SUS) is widely considered a key enzyme participating in sucrose metabolism in higher plants and regarded as a biochemical marker for sink strength in crops. However, despite significant progress in characterizing the physiological functions of the SUS gene family, knowledge of the trajectory of evolutionary processes and significance of the family in higher plants remains incomplete.

RESULTS

In this study, we identified over 100 SUS genes in 19 plant species and reconstructed their phylogenies, presenting a potential framework of SUS gene family evolution in higher plants. Three anciently diverged SUS gene subfamilies (SUS I, II and III) were distinguished based on their phylogenetic relationships and unique intron/exon structures in angiosperms, and they were found to have evolved independently in monocots and dicots. Each subfamily of SUS genes exhibited distinct expression patterns in a wide range of plants, implying that their functional differentiation occurred before the divergence of monocots and dicots. Furthermore, SUS III genes evolved under relaxed purifying selection in dicots and displayed narrowed expression profiles. In addition, for all three subfamilies of SUS genes, the GT-B domain was more conserved than the "regulatory" domain.

CONCLUSIONS

The present study reveals the evolution of the SUS gene family in higher plants and provides new insights into the evolutionary conservation and functional divergence of angiosperm SUS genes.

Effect of simulated warming on the functional traits of Leymus chinensis plant in Songnen grassland

Leymus chinensis grassland in Northeast China provides a natural laboratory for the investigation of climate change. The response of L. chinensis to experimental warming can provide insight into its regeneration behaviour and the likely composition of future communities under warmer climate. We used MSR-2420 infrared radiators to elevate temperature and examined soil organic carbon and nitrogen and soil total phosphorus and determined the growth and physiology of L. chinensis in response to manipulations of ambient condition and warming. Results showed that compared with the control, L. chinensis subjected to warming treatment showed increased soil organic carbon and soil total nitrogen, but no significant difference was observed in soil total phosphorus. Climate warming increased shoot biomass, ecosystem respiration, and ecosystem water-use efficiency and reduced net ecosystem CO2 exchange and evapotranspiration. This result implies that warming could rapidly alter carbon fluxes. The effect of warming treatment significantly increased the contents of glucose and fructose and significantly inhibited sucrose synthesis. However, the TCA cycle was enhanced when citric and malic acid contents further accumulated. The results implied that L. chinensis probably enhanced its warming adaption mechanism mainly through increasing glycolysis consumption when it was exposed to elevated temperature. These results provide an understanding of the fundamental evidence explaining the primary metabolism of L. chinensis in response to warming and suggest the future impact of the terrestrial carbon-cycle feedback on global climate change.