Trehalose 6-phosphate

Starch and sucrose metabolism plays an important role in the stem development in Medicago sativa

The forage quality of alfalfa (Medicago sativa ) stems is greater than the leaves. Sucrose hydrolysis provides energy for stem development, with starch being enzymatically converted into sucrose to maintain energy homeostasis. To understand the physiological and molecular networks controlling stem development, morphological characteristics and transcriptome profiles in the stems of two alfalfa cultivars (Zhungeer and WL168) were investigated. Based on transcriptome data, we analysed starch and sugar contents, and enzyme activity related to starch-sugar interconversion. Zhungeer stems were shorter and sturdier than WL168, resulting in significantly higher mechanical strength. Transcriptome analysis showed that starch and sucrose metabolism were significant enriched in the differentially expressed genes of stems development in both cultivars. Genes encoding INV , bglX , HK , TPS and glgC downregulated with the development of stems, while the gene encoding was AMY upregulated. Weighted gene co-expression network analysis revealed that the gene encoding glgC was pivotal in determining the variations in starch and sucrose contents between the two cultivars. Soluble carbohydrate, sucrose, and starch content of WL168 were higher than Zhungeer. Enzyme activities related to sucrose synthesis and hydrolysis (INV, bglX, HK, TPS) showed a downward trend. The change trend of enzyme activity was consistent with gene expression. WL168 stems had higher carbohydrate content than Zhungeer, which accounted for more rapid growth and taller plants. WL168 formed hollow stems were formed during rapid growth, which may be related to the redistribution of carbohydrates in the pith tissue. These results indicated that starch and sucrose metabolism play important roles in the stem development in alfalfa.

Comparative physiological and transcriptome analysis between potassium-deficiency tolerant and sensitive sweetpotato genotypes in response to potassium-deficiency stress

BACKGROUND

Sweetpotato is a typical ''potassium (K+) favoring'' food crop, which root differentiation process needs a large supply of potassium fertilizer and determine the final root yield. To further understand the regulatory network of the response to low potassium stress, here we analyze physiological and biochemical characteristics, and investigated root transcriptional changes in two sweetpotato genotypes, namely, - K tolerant "Xu32" and - K susceptible"NZ1".

RESULT

We found Xu32 had the higher capability of K+ absorption than NZ1 with better growth performance, higher net photosynthetic rate and higher chlorophyll contents under low potassium stress, and identified 889 differentially expressed genes (DEGs) in Xu32, 634 DEGs in NZ1, 256 common DEGs in both Xu32 and NZ1. The Gene Ontology (GO) term in molecular function enrichment analysis revealed that the DEGs under low K+ stress are predominately involved in catalytic activity, binding, transporter activity and antioxidant activity. Moreover, the more numbers of identified DEGs in Xu32 than that in NZ1 responded to K+-deficiency belong to the process of photosynthesis, carbohydrate metabolism, ion transport, hormone signaling, stress-related and antioxidant system may result in different ability to K+-deficiency tolerance. The unique genes in Xu32 may make a great contribution to enhance low K+ tolerance, and provide useful information for the molecular regulation mechanism of K+-deficiency tolerance in sweetpotato.

CONCLUSIONS

The common and distinct expression pattern between the two sweetpotato genotypes illuminate a complex mechanism response to low potassium exist in sweetpotato. The study provides some candidate genes, which can be used in sweetpotato breeding program for improving low potassium stress tolerance.

Time-resolved systems analysis of the induction of high photosynthetic capacity in Arabidopsis during acclimation to high light

Induction of high photosynthetic capacity is a key acclimation response to high light (HL) for many herbaceous dicot plants; however, the signaling pathways that control this response remain largely unknown. Here, a systems biology approach was utilized to characterize the induction of high photosynthetic capacity in strongly and weakly acclimating Arabidopsis thaliana accessions. Plants were grown for 5 wk in a low light (LL) regime, and time-resolved photosynthetic physiological, metabolomic, and transcriptomic responses were measured during subsequent exposure to HL. The induction of high nitrogen (N) assimilation rates early in the HL shift was strongly predictive of the induction of photosynthetic capacity later in the HL shift. Accelerated N assimilation rates depended on the mobilization of existing organic acid (OA) reserves and increased de novo OA synthesis during the induction of high photosynthetic capacity. Enhanced sucrose biosynthesis capacity increased in tandem with the induction of high photosynthetic capacity, and increased starch biosynthetic capacity was balanced by increased starch catabolism. This systems analysis supports a model in which the efficient induction of N assimilation early in the HL shift begins the cascade of events necessary for the induction of high photosynthetic capacity acclimation in HL.

Leaf senescence attributes: the novel and emerging role of sugars as signaling molecules and the overlap of sugars and hormones signaling nodes

Sugars are the primary products of photosynthesis and play multiple roles in plants. Although sugars are usually considered to be the building blocks of energy storage and carbon transport molecules, they have also gradually come to be acknowledged as signaling molecules that can initiate senescence. Senescence is an active and essential process that occurs at the last developmental stage and corresponds to programmed degradation of: cells, tissues, organs, and entire organisms. It is a complex process involving: numerous biochemical changes, transporters, genes, and transcription factors. The process is controlled by multiple developmental signals, among which sugar signals are considered to play a vital role; however, the regulatory pathways involved are not fully understood. The dynamic mechanistic framework of sugar accumulation has an inconsistent effect on senescence through the sugar signaling pathway. Key metabolizing enzymes produce different sugar signals in response to the onset of senescence. Diverse sugar signal transduction pathways and a variety of sugar sensors are involved in controlling leaf senescence. This review highlights the processes underlying initiation of sugar signaling and crosstalk between sugars and hormones signal transduction pathways affecting leaf senescence. This summary of the state of current knowledge across different plants aids in filling knowledge gaps and raises key questions that remain to be answered with respect to regulation of leaf senescence by sugar signaling pathways.

The trehalose 6-phosphate phosphatase family in plants

Trehalose 6-phosphate (Tre6P), the intermediate of trehalose biosynthesis, is an essential signalling metabolite linking plant growth and development to carbon metabolism. While recent work has focused predominantly on the enzymes that produce Tre6P, little is known about the proteins that catalyse its degradation, the trehalose 6-phosphate phosphatases (TPPs). Often occurring in large protein families, TPPs exhibit cell-, tissue- and developmental stage-specific expression patterns, suggesting important regulatory functions in controlling local levels of Tre6P and trehalose as well as Tre6P signalling. Furthermore, growing evidence through gene expression studies and transgenic approaches shows that TPPs play an important role in integrating environmental signals with plant metabolism. This review highlights the large diversity of TPP isoforms in model and crop plants and identifies how modulating Tre6P metabolism in certain cell types, tissues, and at different developmental stages may promote stress tolerance, resilience and increased crop yield.

De novo transcriptome sequencing of drought tolerance-associated genes in little millet (Panicum sumatrense L.)

The genome size of the little millet Panicum sumatrense is unknown, although its genome is fairly diploid (2n = 4x = 36). Despite tremendous nutritional value and adaptability to adverse climatic conditions, P. sumatrense use was limited by their low palatability, coarse grain, and lack of variety of culinary preparations. Hence, understanding how to vary their usage to offer food and nutritional security in the continuously changing modern world, the proposed study was aimed to determine potential genes and metabolites implicated in drought resistance. The drought-resistant genotype of tiny millet OLM-203/Tarini was offered in pots under both relaxed and demanding circumstances. The experimental seedlings were 32 days old and had been under water stress for 23 days. A total of 7606 genes were compared between 23 and 32 days for roots and 7264 total genes were compared between 23 and 32 days for leaves, according to a research on differential expression genes (DEGs). Twenty essential genes for drought tolerance were up-or down-regulated in the control and treated roots of the OLM-203 genotype. For instance, the genes RS193 and XB34 were up-regulated in leaves while, WLIM1 was found to be down-regulated. Gene SKI35 was up-regulated in roots, whereas MPK6 and TCMOp1 were down-regulated in root samples. The roots and leaves of the tiny millet OLM-203 genotype expressed 36 up-regulated and 21 down-regulated serine transcripts, respectively. Gene annotations for leaf samples were classified as having "molecular function" (46%), "cellular component" (19%), and "biological process" (35%), while root sample gene annotations were categorized as having "biological process" (573 contigs), "molecular function" (401 contigs), and "cellular components" (166 contigs). Noteworthy, polyamines play a crucial role in drought stress tolerance in the genotype, and it was found that top ten DEGs encoding for polyamines were common in two tissues (leaf and root). Collectively, transcriptomics profiling (RNA-seq) unveiled transcriptional stability drought stress provide a new insight in underlying modus of operandi in little millet genotype "OLM-203/Tarini" in response to heat stress.

Non-structural carbohydrates contributed to cold tolerance and regeneration of Medicago sativa L

MAIN CONCLUSION

Soil water content only affected regeneration time, whereas the NSC content was related to the success of alfalfa regeneration. Non-structural carbohydrates (NSCs) are important factors influencing the overwintering and regeneration of alfalfa. In this study, we analyzed eight in-situ samplings at three depths of coarse roots (crown, 20 and 40 cm depths) during the overwintering period and assessed the dynamic change and allocation of root NSCs under three irrigation frequencies (irrigation once every second day/4 days/8 days). Primary results showed that: (i) before cold acclimation, irrigation once every second day was beneficial to the accumulation of soluble sugars and starch in crown tissues, which would be maintained until the following spring and accelerate the regeneration time of alfalfa; (ii) during the overwintering process, the soluble sugars and starch contents in the crown were significantly higher than those in deeper roots, and there was an asynchronous effect caused by the change in soluble sugars and starch among roots at three depths; and (iii) the change trend of soluble sugar and starch contents was consistent with that of semi-lethal temperature, and there was a significant negative correlation between the content of soluble sugar (R² = 0.8046) and starch (R² = 0.6332) and the semi-lethal temperature. This study demonstrated that NSCs are the key driver of cold tolerance and regeneration under the three irrigation frequencies evaluated. Our results provide further insight into the allocation of NSCs in winter. This improved understanding of the mechanism of overwintering will allow for improved water management of alfalfa in high latitude areas.

Sugars and sucrose transporters in pollinia of Phalaenopsis aphrodite (Orchidaceae)

The pollen grains of Phalaenopsis orchids are clumped tightly together, packed in pollen dispersal units called pollinia. In this study, the morphology, cytology, biochemistry, and sucrose transporters in pollinia of Phalaenopsis orchids were investigated. Histochemical detection was used to characterize the distribution of sugars and callose at the different development stages of pollinia. Ultra-performance liquid chromatography-high resolution-tandem mass spectrometry data indicated that P. aphrodite accumulated abundant saccharides such as sucrose, galactinol, myo-inositol, and glucose, and trace amounts of raffinose and trehalose in mature pollinia. We found that galactinol synthase (PAXXG304680) and trehalose-6-phosphate phosphatase (PAXXG016120) genes were preferentially expressed in mature pollinia. The P. aphrodite genome was identified as having 11 sucrose transporters (SUTs). Our qRT-PCR confirmed that two SUTs (PAXXG030250 and PAXXG195390) were preferentially expressed in the pollinia. Pollinia germinated in pollen germination media (PGM) supplemented with 10% sucrose showed increased callose production and enhanced pollinia germination, but there was no callose or germination in PGM without sucrose. We show that P. aphrodite accumulates high levels of sugars in mature pollinia, providing nutrients and enhanced SUT gene expression for pollinia germination and tube growth.

Genome-Wide Identification and Analysis of Stress Response of Trehalose-6-Phosphate Synthase and Trehalose-6-Phosphate Phosphatase Genes in Quinoa

Saline-alkali stress seriously affects the yield and quality of crops, threatening food security and ecological security. Improving saline-alkali land and increasing effective cultivated land are conducive to sustainable agricultural development. Trehalose, a nonreducing disaccharide, is closely related to plant growth and development and stress response. Trehalose 6-phosphate synthase (TPS) and trehalose-6-phosphate phosphatase (TPP) are key enzymes catalyzing trehalose biosynthesis. To elucidate the effects of long-term saline-alkali stress on trehalose synthesis and metabolism, we conducted an integrated transcriptome and metabolome analysis. As a result, 13 TPS and 11 TPP genes were identified in quinoa (Chenopodium quinoa Willd.) and were named CqTPS1-13 and CqTPP1-11 according to the order of their Gene IDs. Through phylogenetic analysis, the CqTPS family is divided into two classes, and the CqTPP family is divided into three classes. Analyses of physicochemical properties, gene structures, conservative domains and motifs in the proteins, and cis-regulatory elements, as well as evolutionary relationships, indicate that the TPS and TPP family characteristics are highly conserved in quinoa. Transcriptome and metabolome analyses of the sucrose and starch metabolism pathway in leaves undergoing saline-alkali stress indicate that CqTPP and Class II CqTPS genes are involved in the stress response. Moreover, the accumulation of some metabolites and the expression of many regulatory genes in the trehalose biosynthesis pathway changed significantly, suggesting the metabolic process is important for the saline-alkali stress response in quinoa.

Combined metabolomic and transcriptomic analysis reveals key components of OsCIPK17 overexpression improves drought tolerance in rice

Oryza Sativa is one of the most important food crops in China, which is easily affected by drought during its growth and development. As a member of the calcium signaling pathway, CBL-interacting protein kinase (CIPK) plays an important role in plant growth and development as well as environmental stress. However, there is no report on the function and mechanism of OsCIPK17 in rice drought resistance. We combined transcriptional and metabonomic analysis to clarify the specific mechanism of OsCIPK17 in response to rice drought tolerance. The results showed that OsCIPK17 improved drought resistance of rice by regulating deep roots under drought stress; Response to drought by regulating the energy metabolism pathway and controlling the accumulation of citric acid in the tricarboxylic acid (TCA) cycle; Our exogenous experiments also proved that OsCIPK17 responds to citric acid, and this process involves the auxin metabolism pathway; Exogenous citric acid can improve the drought resistance of overexpression plants. Our research reveals that OsCIPK17 positively regulates rice drought resistance and participates in the accumulation of citric acid in the TCA cycle, providing new insights for rice drought resistance.

A comparative proteomic analysis provides insight into the molecular mechanism of bud break in longan

BACKGROUND

The timing of bud break is very important for the flowering and fruiting of longan. To obtain new insights into the underlying regulatory mechanism of bud break in longan, a comparative analysis was conducted in three flower induction stages of two longan varieties with opposite flowering phenotypes by using isobaric tags for relative and absolute quantification (iTRAQ).

RESULTS

In total, 3180 unique proteins were identified in 18 samples, and 1101 differentially abundant proteins (DAPs) were identified. "SX" ("Shixia"), a common longan cultivated variety that needs an appropriate period of low temperatures to accumulate energy and nutrients for flower induction, had a strong primary inflorescence, had a strong axillary inflorescence, and contained high contents of sugars, and most DAPs during the bud break process were enriched in assimilates and energy metabolism. Combined with our previous transcriptome data, it was observed that sucrose synthase 6 (SS6) and granule-bound starch synthase 1 (GBSSI) might be the key DAPs for "SX" bud break. Compared to those of "SX", the primary inflorescence, axillary inflorescence, floral primordium, bract, and prophyll of "SJ" ("Sijimi") were weaker. In addition, light, rather than a high sugar content or chilling duration, might act as the key signal for triggering bud break. In addition, catalase isozyme 1, an important enzyme in the redox cycle, and RuBisCO, a key enzyme in the Calvin cycle of photosynthetic carbon assimilation, might be the key DAPs for SJ bud break.

CONCLUSION

Our results present a dynamic picture of the bud break of longan, not only revealing the temporal specific expression of key candidate genes and proteins but also providing a scientific basis for the genetic improvement of this fruit tree species.

Study protocol for a pilot randomised controlled trial evaluating the effectiveness of oral trehalose on inflammatory factors, oxidative stress, nutritional and clinical status in traumatic head injury patients receiving enteral nutrition

INTRODUCTION

In traumatic brain injury (TBI) patients, inflammatory processes and oxidative stress have been linked to the development of neurodegenerative diseases, disability, increased rate of muscle catabolism, malnutrition, hospital stay and mortality. Previous in vitro and in vivo studies have shown that trehalose can decrease inflammatory and oxidative factors. Therefore, the present study was designed to evaluate the effect of oral trehalose consumption on this marker in critically ill TBI patients at intensive care unit (ICU).

METHODS AND ANALYSIS

This study is a pilot randomised, prospective and double-blind clinical trial. The study sample size is of 20 (10 patients in each group) TBI patients aged 18-65 years at ICU. Randomisation is performed by permuted block randomisation method. The allocation ratio is 1:1. An intervention group will receive 30 g of trehalose instead, as a part of the carbohydrate of daily bolus enteral feeding and the control group will receive standard isocaloric hospital bolus enteral feeding for 12 days. The inflammatory factors (C reactive protein, interleukin 6) and oxidative stress markers (glutathione, malondialdehyde, superoxide dismutase, pro-oxidant-antioxidant balance, total antioxidant capacity) will be measured at the baseline, at the 6th day, and at the end of the study (12th day). Sequential Organ Failure Assessment, Acute Physiology and Chronic Health Evaluation II, Nutrition Risk in the Critically ill scores, 28-day mortality, anthropometric assessments and the clinical and nutritional status will be measured. Each patient's nutritional needs will be calculated individually. The statistical analysis would be based on the intention to treat.

ETHICS AND DISSEMINATION

The vice-chancellor of the research centre of Mashhad University of Medical Sciences is sponsoring this study. IR.MUMS.MEDICAL.REC.1400.113.

TRIAL REGISTRATION NUMBER

Iranian Registry of Clinical Trials (IRCT) Id: IRCT20210508051223N1, Registration date: 26 July 2021.

Comparative Study of Trehalose and Trehalose 6-Phosphate to Improve Antioxidant Defense Mechanisms in Wheat and Mustard Seedlings under Salt and Water Deficit Stresses

Trehalose 6-phosphate (T6P) regulates sugar levels and starch metabolism in a plant cell and thus interacts with various signaling pathways, and after converting T6P into trehalose (Tre), it acts as a vital osmoprotectant under stress conditions. This study was conducted using wheat (Triticum aestivum L. cv. Norin 61) and mustard (Brassica juncea L. cv. BARI sharisha 13) seedlings to investigate the role of Tre and T6P in improving salt and water deficit stress tolerance. The seedlings were grown hydroponically using Hyponex solution and exposed to salt (300 and 200 mM NaCl for wheat and mustard, respectively) and water deficit (20 and 12% PEG 6000 for wheat and mustard, respectively) stresses with or without Tre and T6P. The study demonstrated that salt and water deficit stress negatively influenced plant growth by destroying photosynthetic pigments and increasing oxidative damage. In response to salt and water deficit stresses, the generation of H2O2 increased by 114 and 67%, respectively, in wheat seedlings, while in mustard, it increased by 86 and 50%, respectively. Antioxidant defense systems were also altered by salt and water deficit stresses due to higher oxidative damage. The AsA content was reduced by 65 and 38% in wheat and 61 and 45% in mustard under salt and water deficit stresses, respectively. The subsequent negative results of salinity and water deficit can be overcome by exogenous application of Tre and T6P; these agents reduced the oxidative stress by decreasing H2O2 and TBARS levels and increasing enzymatic and non-enzymatic antioxidants. Moreover, the application of Tre and T6P decreased the accumulation of Na in the shoots and roots of wheat and mustard seedlings. Therefore, the results suggest that the use of Tre and T6P is apromising strategy to alleviate osmotic and ionic toxicity in plants under salt and water deficit stresses.

Investigation of sugar signaling behaviors involved in sucrose-induced senescence initiation and progression in N. tabacum

Sugar is involved in initiating leaf senescence. However, its regulatory role, especially as a signal in the senescence process, is unclear. Therefore, this study was designed to illustrate how sugar stimulates the onset of leaf senescence and controls sugar homeostasis through the T6P-SnRK (sucrose non-fermenting (SNF)-related kinase) and HXK (hexokinase) signaling pathways. We used a leaf disc system detached from fully expanded leaves of Nicotiana tabacum cv. K326 and designed a time-course study (days 3, 5, 7, and 9) with exogenously gradient concentrations (0, 30, 60, 90, 120, and 150 mM) of sucrose (Suc) treatment to identify how Suc application affects sugar metabolism and induces senescence. Our results revealed that early decreases of Fv/Fm and increases in electrolyte leakage responded to Suc on day 3. Furthermore, a substantial increase in lipid peroxidation and up-regulated expression of senescence marker genes (NtSAG12) (except 60 mM on day 3) responded sequentially by day 5. The glucose, G6P, and HXK contents were first induced by Suc on day 3 and then repressed from day 5 to day 7. However, exogenous Suc treatment significantly improved the TPS content and the subsequent precursor T6P from day 3 to day 7. Following exogenous Suc treatments, the transcript level of NtSnRK1 was markedly down-regulated from day 3 to day 7. On the other hand, a linear regression analysis demonstrated that the T6P-NtSnRK1 signaling pathway was strongly associated with senescence initiation, and was accompanied by membrane degradation and NtCP1/NtSAG12 up-regulation by day 3. The T6P-NtSnRK1 signaling pathway experienced membrane and chloroplast degradation by day 5. HXK functioned as a metabolic enzyme promoting Glc-G6P and as a Glc sensor, accelerating the initiation of senescence through the HXK-dependent pathway by repressing PSII by day 3 and the senescence process through the Glycolytic pathway by day 7. These physiological, biochemical, and molecular analyses demonstrate that exogenous Suc regulates T6P accumulation, inducing senescence through the NtSnRK signaling pathway. These results illustrate the role of Suc and the transition of the sugar signaling pathway during the progression of senescence initiation.

Trehalose Outperforms Chitosan, Humic Acid and Gamma-Aminobutyric Acid in Promoting the Growth of Field Maize

Despite the fact that there are many distinct types of plant growth regulators (PGRs), the diverse ways in which they regulate plant development are rarely compared. In this study, four PGRs (trehalose, chitosan, humic acid and gamma-aminobutyric acid) were selected and sprayed folially, and plant samples were collected while maize was at vegetative leaf stages 6, 10, and 14 (V6, V10, and V14, respectively) to reveal the effects of different PGRs on photosynthesis, dry matter accumulation, oxidative stress, carbon and nitrogen metabolism, hormone levels, and gene expression of maize. Results showed that 100 mg/L PGRs did not induce oxidative damage or repair activities in maize. Trehalose significantly increased chlorophyll content at V6 and promoted dry matter (roots and shoots) accumulation at V6 and V10. The activities of carbon and nitrogen metabolizing enzymes were significantly enhanced by trehalose treatment, which promoted the accumulation of sucrose and soluble sugar, but did not affect the biosynthesis of auxin and gibberellin at V6. Changes in carbon and nitrogen metabolism enzymes are regulated by transcription of related synthetic genes. Lower starch content and higher sucrose content in trehalose-treated maize leaves are important biological characteristics. Further analysis revealed that the effect of trehalose on the metabolic activity of maize was a short-term promoting effect (0-12 days), while the effect on maize growth was a long-term cumulative effect (13-28 days). Overall, exogenous trehalose induced stronger carbon and nitrogen metabolic activity, higher photosynthetic capacity and more dry matter accumulation than chitosan, humic acid and gamma-aminobutyric acid.

Trehalose increases tomato drought tolerance, induces defenses, and increases resistance to bacterial wilt disease

Ralstonia solanacearum causes bacterial wilt disease, leading to severe crop losses. Xylem sap from R. solanacearum-infected tomato is enriched in the disaccharide trehalose. Water-stressed plants also accumulate trehalose, which increases drought tolerance via abscisic acid (ABA) signaling. Because R. solanacearum-infected plants suffer reduced water flow, we hypothesized that bacterial wilt physiologically mimics drought stress, which trehalose could mitigate. We found that R. solanacearum-infected plants differentially expressed drought-associated genes, including those involved in ABA and trehalose metabolism, and had more ABA in xylem sap. Consistent with this, treating tomato roots with ABA reduced both stomatal conductance and stem colonization by R. solanacearum. Treating roots with trehalose increased xylem sap ABA and reduced plant water use by lowering stomatal conductance and temporarily improving water use efficiency. Trehalose treatment also upregulated expression of salicylic acid (SA)-dependent tomato defense genes; increased xylem sap levels of SA and other antimicrobial compounds; and increased bacterial wilt resistance of SA-insensitive NahG tomato plants. Additionally, trehalose treatment increased xylem concentrations of jasmonic acid and related oxylipins. Finally, trehalose-treated plants were substantially more resistant to bacterial wilt disease. Together, these data show that exogenous trehalose reduced both water stress and bacterial wilt disease and triggered systemic disease resistance, possibly through a Damage Associated Molecular Pattern (DAMP) response pathway. This suite of responses revealed unexpected linkages between plant responses to biotic and abiotic stress and suggested that R. solanacearum-infected plants increase trehalose to improve water use efficiency and increase wilt disease resistance. The pathogen may degrade trehalose to counter these efforts. Together, these results suggest that treating tomatoes with exogenous trehalose could be a practical strategy for bacterial wilt management.

Microbial trehalose boosts the ecological fitness of biocontrol agents, the viability of probiotics during long-term storage and plants tolerance to environmental-driven abiotic stress

Despite the impressive gain in agricultural production and greater availability of food, a large portion of the world population is affected by food shortages and nutritional imbalance. This is due to abiotic stresses encountered by plants as a result of environmental-driven perturbations, loss of viability of starter cultures (probiotics) for functional foods during storage as well as the vulnerability of farm produce to postharvest pathogens. The use of compatible solutes (e.g., trehalose, proline, etc.) has been widely supported as a solution to these concerns. Trehalose is one of the widely reported microbial- or plant-derived metabolites that help microorganisms (e.g., biocontrol agents, probiotics and plant growth-promoting bacteria) and plants to tolerate harsh environmental conditions. Due to its recent categorization as generally regarded as safe (GRAS), trehalose is an essential tool for promoting nutrition-sensitive agriculture by replacing the overuse of chemical agents (e.g., pesticides, herbicides). Therefore, the current review evaluated the progress currently made in the application of trehalose in sustainable agriculture. The challenges, opportunities, and future of this biometabolite in food security were highlighted.

Integrated Metabolomics and Transcriptome Analyses Unveil Pathways Involved in Sugar Content and Rind Color of Two Sugarcane Varieties

Metabolic composition can have potential impact on several vital agronomic traits, and metabolomics, which represents the bioactive compounds in plant tissues, is widely considered as a powerful approach for linking phenotype-genotype interactions. However, metabolites related to cane traits such as sugar content, rind color, and texture differences in different sugarcane cultivars using metabolome integrated with transcriptome remain largely inconclusive. In this study, metabolome integrated with transcriptome analyses were performed to identify and quantify metabolites composition, and have better insight into the molecular mechanisms underpinning the different cane traits, namely, brix, rind color, and textures in the stems (S) and leaves (L) of sugarcane varieties FN41 and 165402. We also identified metabolites and associated genes in the phenylpropanoid and flavonoid biosynthesis pathways, starch and sucrose metabolism. A total of 512 metabolites from 11 classes, with the vast majority (122) belonging to flavonoids were identified. Moreover, the relatively high amount of D-fructose 6-p, D-glucose6-p and glucose1-p detected in FN41L may have been transported and distributed by source and sink of the cane, and a majority of them reached the stem of sugarcane FN41L, thereby promoting the high accumulation of sugar in FN41S. Observations also revealed that genes such as C4H, CHS, F3H, F3'H, DFR, and FG2 in phenylpropanoid and flavonoid biosynthesis pathways were the major factors impacting the rind color and contrasting texture of FN41 and 165204. Further analysis revealed that weighted gene co-expression network analysis (WGCNA) hub genes and six transcription factors, namely, Tify and NAC, MYB-related, C2C2-Dof, WRKY, and bHLH play a key role in phenylpropanoid biosynthesis, flavone and flavonol biosynthesis, starch and sucrose metabolism. Additionally, metabolites such as L-phenylalanine, tyrosine, sinapaldehyde, pinobanksin, kaempferin, and nictoflorin were the potential drivers of phenotypic differences. Our finding also demonstrated that genes and metabolites in the starch and sucrose metabolism had a significant effect on cane sugar content. Overall, this study provided valuable insight into the molecular mechanisms underpinning high sugar accumulation and rind color in sugarcane, which we believe is important for future sugarcane breeding programs and the selection of high biomass varieties.

Genome-Wide Identification and Characterization of the Trehalose-6-phosphate Synthetase (TPS) Gene Family in Watermelon (Citrullus lanatus) and Their Transcriptional Responses to Salt Stress

With the increase in watermelon cultivation area, there is an urgent need to explore enzymatic and genetic resources for the sustainable development of watermelon, especially under salt stress. Among the various compounds known, trehalose plays an important role in regulating abiotic stress tolerances in diverse organisms, including plants. Therefore, the present study comprehensively analyzed the trehalose-6-phosphate synthase (TPS) gene family in watermelon. The study analyzed the functional classification, evolutionary characteristics, and expression patterns of the watermelon TPS genes family. Seven ClTPSs were identified and classified into two distinct classes according to gene structure and phylogeny. Evolutionary analysis suggested the role of purifying selection in the evolution of the TPS family members. Further, cis-acting elements related to plant hormones and abiotic stress were identified in the promoter region of the TPS genes. The tissue-specific expression analysis showed that ClTPS genes were widely expressed in roots, stems, leaves, flowers, and fruits, while ClTPS3 was significantly induced under salt stress. The overexpression of ClTPS3 in Arabidopsis thaliana significantly improved salt tolerance. Finally, the STRING functional protein association networks suggested that the transcription factor ClMYB and ClbHLH regulate ClTPS3. Thus, the study indicates the critical role of ClTPS3 in watermelon response to salt stress.

Trehalose treatment alters carbon partitioning and reduces the accumulation of individual metabolites but does not affect salt tolerance in the green microalga Dunaliella bardawil

The effects of trehalose (Tre), a non-reducing disaccharide, on metabolic changes, antioxidant status, and salt tolerance in Dunaliella bardawil cells were investigated. Algal suspensions containing 1, 2, and 3 M NaCl were treated with 5 mM Tre. While the content of pigments, reducing sugars, proteins, glycerol, and ascorbate pool accumulated with increasing salinity, the content of non-reducing sugars, starch, amino acids, proline, hydrogen peroxide, and lipid peroxidation level decreased significantly. Tre-treated cells showed a decrease in pigments content, reducing sugars, starch, proteins, amino acids, proline, glycerol, and the activity of non-specific peroxidase and polyphenol oxidase, but an increase in non-reducing sugars, oxidized ascorbate, and ascorbate peroxidase activity occurred unchanged in the ascorbate pool. However, the density and fresh weight of the cells remained statistically unchanged in all Tre-treated and untreated cultures. These results suggest that D. bardawil cells potentially tolerate different salt levels by accumulating metabolites, whereas Tre treatment changes carbon partitioning and significantly reduces beneficial metabolites without altering salt tolerance. Therefore, the regulation of carbon partitioning rather than the amount of assimilated carbon may play an important role in inducing salinity tolerance of D. bardawil. However, Tre is not able to enhance the salt tolerance of halotolerants and is even economically damaging due to the reduction of unique metabolites such as glycerol and β-carotene.

External and Internal Reshaping of Plant Thermomorphogenesis

Plants dynamically adapt to changing temperatures to ensure propagation and reproductive success, among which morphogenic responses to warm temperatures have been extensively studied in recent years. As readily inferred from the cyclic co-oscillations of environmental cues in nature, plant thermomorphogenesis is coordinately reshaped by various external conditions. Accumulating evidence supports that internal and developmental cues also contribute to harmonizing thermomorphogenic responses. The external and internal reshaping of thermomorphogenesis is facilitated by versatile temperature sensing and interorgan communication processes, circadian and photoperiodic gating of thermomorphogenic behaviors, and their metabolic coordination. Here, we discuss recent advances in plant thermal responses with focus on the diel and seasonal reshaping of thermomorphogenesis and briefly explore its application to developing climate-smart crops.

Parallel evolution of trehalose production machinery in anhydrobiotic animals via recurrent gene loss and horizontal transfer

Trehalose is a versatile non-reducing sugar. In some animal groups possessing its intrinsic production machinery, it is used as a potent protectant against environmental stresses, as well as blood sugar. However, the trehalose biosynthesis genes remain unidentified in the large majority of metazoan phyla, including vertebrates. To uncover the evolutionary history of trehalose production machinery in metazoans, we scrutinized the available genome resources and identified bifunctional trehalose-6-phosphate synthase-trehalose-6-phosphate phosphatase (TPS–TPP) genes in various taxa. The scan included our newly sequenced genome assembly of a desiccation-tolerant tardigrade Paramacrobiotus sp. TYO, revealing that this species retains TPS–TPP genes activated upon desiccation. Phylogenetic analyses identified a monophyletic group of the many of the metazoan TPS–TPP genes, namely ‘pan-metazoan’ genes, that were acquired in the early ancestors of metazoans. Furthermore, coordination of our results with the previous horizontal gene transfer studies illuminated that the two tardigrade lineages, nematodes and bdelloid rotifers, all of which include desiccation-tolerant species, independently acquired the TPS–TPP homologues via horizontal transfer accompanied with loss of the ‘pan-metazoan’ genes. Our results indicate that the parallel evolution of trehalose synthesis via recurrent loss and horizontal transfer of the biosynthesis genes resulted in the acquisition and/or augmentation of anhydrobiotic lives in animals.

Integrated transcriptome and metabolome analysis reveals molecular responses of the clams to acute hypoxia

Mudflat shellfish have evolved well-adapted strategies for coping with dynamic environmental fluxes and stressful conditions, including oxygen availability. The Manila clams Ruditapes philippinarum are worldwide cultured shellfish in marine intertidal zone, which usually encounter great risk of acute hypoxia exposure in coastal habitats. To reveal the effects of acute hypoxia on metabolic changes of the clams, we performed the integrated analysis of transcriptomics and metabolomics to investigate the global changes of genes and metabolites during acute hypoxia stress at the whole-organism level. The comparative transcriptome analysis reveals that the clams show the remarkable depression in a variety of biological performance, such as metabolic rates, neuronal activity, biomineralization activity, and cell proliferation and differentiation at the hypoxic condition. The metabolomic analysis reveals that amino acid metabolism plays a critical role in the metabolic changes of the clams in response to acute hypoxia. A variety of free amino acids may not only be served as the potential osmolytes for osmotic regulation, but also may contribute to energy production during the acute hypoxia exposure. The metabolite analysis also reveals several important biomarkers for metabolic changes, and provides new insights into how clams deal with acute hypoxia. These findings suggest that clams may get through acute hypoxia stress by the adaptive metabolic strategy to survive short-period of acute hypoxia which is likely to occur in their typical habitat. The present findings will not only shed lights on the molecular and metabolic mechanisms of adaptive strategies under stressful conditions, but also provide the signaling metabolites to assess the physiological states of clams in aquaculture.

Central Metabolism in Mammals and Plants as a Hub for Controlling Cell Fate

Significance: The importance of oxidoreductases in energy metabolism together with the occurrence of enzymes of central metabolism in the nucleus gave rise to the active research field aiming to understand moonlighting enzymes that undergo post-translational modifications (PTMs) before carrying out new tasks. Recent Advances: Cytosolic enzymes were shown to induce gene transcription after PTM and concomitant translocation to the nucleus. Changed properties of the oxidized forms of cytosolic glyceraldehyde 3-phosphate dehydrogenase, and also malate dehydrogenases and others, are the basis for a hypothesis suggesting moonlighting functions that directly link energy metabolism to adaptive responses required for maintenance of redox-homeostasis in all eukaryotes. Critical Issues: Small molecules, such as metabolic intermediates, coenzymes, or reduced glutathione, were shown to fine-tune the redox switches, interlinking redox state, metabolism, and induction of new functions via nuclear gene expression. The cytosol with its metabolic enzymes connecting energy fluxes between the various cell compartments can be seen as a hub for redox signaling, integrating the different signals for graded and directed responses in stressful situations. Future Directions: Enzymes of central metabolism were shown to interact with p53 or the assumed plant homologue suppressor of gamma response 1 (SOG1), an NAM, ATAF, and CUC transcription factor involved in the stress response upon ultraviolet exposure. Metabolic enzymes serve as sensors for imbalances, their inhibition leading to changed energy metabolism, and the adoption of transcriptional coactivator activities. Depending on the intensity of the impact, rerouting of energy metabolism, proliferation, DNA repair, cell cycle arrest, immune responses, or cell death will be induced. Antioxid. Redox Signal. 34, 1025-1047.

An L-type lectin receptor-like kinase promotes starch accumulation during rice pollen maturation

Starch accumulation is key for the maturity of rice pollen grains; however, the regulatory mechanism underlying this process remains unknown. Here, we have isolated a male-sterile rice mutant, abnormal pollen 1 (ap1), which produces nonviable pollen grains with defective starch accumulation. Functional analysis revealed that AP1 encodes an active L-type lectin receptor-like kinase (L-LecRLK). AP1 is localized to the plasma membrane and its transcript is highly accumulated in pollen during the starch synthesis phase. RNA-seq and phosphoproteomic analysis revealed that the expression/phosphorylation levels of numerous genes/proteins involved in starch and sucrose metabolism pathway were significantly altered in the mutant pollen, including a known rice UDP-glucose pyrophosphorylase (OsUGP2). We further found that AP1 physically interacts with OsUGP2 to elevate its enzymatic activity, likely through targeted phosphorylation. These findings revealed a novel role of L-LecRLK in controlling pollen maturity via modulating sucrose and starch metabolism.

MYB61 is regulated by GRF4 and promotes nitrogen utilization and biomass production in rice

Nitrogen (N) is a macronutrient that boosts carbon (C) metabolism and plant growth leading to biomass accumulation. The molecular connection between nitrogen utilization efficiency (NUE) and biomass production remains unclear. Here, via quantitative trait loci analysis and map-based cloning, we reveal that natural variation at the MYB61 locus leads to differences in N use and cellulose biogenesis between indica and japonica subspecies of rice. MYB61, a transcriptional factor that regulates cellulose synthesis, is directly regulated by a known NUE regulator GROWTH-REGULATING FACTOR4 (GRF4), which coordinates cellulosic biomass production and N utilization. The variation at MYB61 has been selected during indica and japonica domestication. The indica allele of MYB61 displays robust transcription resulting in higher NUE and increased grain yield at reduced N supply than that of japonica. Our study hence unravels how C metabolism is linked to N uptake and may provide an opportunity to reduce N use for sustainable agriculture.

The molecular connection between nitrogen utilization efficiency (NUE) and biomass production is unclear. Here, the authors show that differences in NUE and cellulose biogenesis between rice indica and japonica subspecies can be explained by variation at the MYB61 locus, which is regulated by the NUE regulator GRF4.

Sensitive analysis of trehalose-6-phosphate and related sugar phosphates in plant tissues by chemical derivatization combined with hydrophilic interaction liquid chromatography-tandem mass spectrometry

Trehalose-6-phosphate (T6P) is an important signaling metabolite that is involved in many physiological processes. However, the mechanism of the biological functions of T6P is not fully understood. Quantification of T6P in plants will be beneficial to elucidate the mechanism. However, it is still a challenge to chromatographically separate and sensitively detect T6P and related sugar phosphates. In the current study, we developed a method for effective separation and sensitive detection of glucose-1-phosphate (G1P), glucose-6-phosphate (G6P), sucrose-6-phosphate (S6P) and T6P in plant tissues by chemical derivatization combined with hydrophilic interaction liquid chromatography-tandem mass spectrometry (ChD-HILIC-MS/MS). With this method, two pairs of isomers (G1P/G6P and S6P/T6P) could be well separated on a HILIC column and sensitively detected by MS with limits of detection (LODs) ranging from 0.1 to 0.6 ng mL^-1. The developed method was successfully applied to the detection of endogenous G1P, G6P, S6P and T6P in small amounts of plant tissues, such as 1 mg fresh weight of Oryza sativa shoot.

Transcription profiles reveal the regulatory mechanisms of spur bud changes and flower induction in response to shoot bending in apple (Malus domestica Borkh.)

Shoot bending, as an effective agronomic measure, has been widely used to promote flowering in 'Fuji' apple trees. Here, we examined the transcriptional responses of genes in 'Fuji' apple buds at different flowering stages under a shoot-bending treatment using RNA sequencing. A complex genetic crosstalk-regulated network, involving abscisic acid-related genes, starch metabolism and circadian rhythm-related genes, as well as stress response-related genes, was up-regulated by shoot bending, in which were contrbuted to apple flower bud formation in response to shoot-bending conditions. Flower induction plays an important role in the apple tree life cycle, but young trees produce fewer and inferior flower buds. Shoot bending, as an effective agronomic measure, has been widely used to promote flowering in 'Fuji' apple trees. However, little is known about the gene expression network patterns and molecular regulatory mechanisms caused by shoot bending during the induced flowering. Here, we examined the transcriptional responses of genes in 'Fuji' apple buds at different flowering stages under a shoot-bending treatment using RNA sequencing. A steady up-regulation of carbon metabolism-related genes led to relatively high levels of sucrose in early induced flowering stages and starch accumulation during shoot bending. Additionally, global gene expression profiling determined that cytokinin, indole-3-acetic acid, gibberellin synthesis and signalling-related genes were significantly regulated by shoot bending, contributing to cell division and differentiation, bud growth and flower induction. A complex genetic crosstalk-regulated network, involving abscisic acid-related genes, starch metabolism- and circadian rhythm-related genes, as well as stress response-related genes, was up-regulated by shoot bending. Additionally, some transcription factor family genes that were involved in sugar, abscisic acid and stress response signalling were significantly induced by shoot bending. These important flowering genes, which were mainly involved in photoperiod, age and autonomous pathways, were up-regulated by shoot bending. Thus, a complex genetic network of regulatory mechanisms involved in sugar, hormone and stress response signalling pathways may mediate the induction of apple tree flowering in response to shoot-bending conditions.

Unigene-based RNA-seq provides insights on drought stress responses in Marsdenia tenacissima

Marsdenia tenacissima is a well-known anti-cancer medicinal plant used in traditional Chinese medicine, which often grows on the karst landform and the water conservation capacity of land is very poorly and drought occurrences frequently. We found M. tenacissima has strong drought resistance because of continuousdrought16 d, the leaves of M. tenacissima were fully curly and dying. But the leaves were fully almost recovering after re-watering 24h. The activity of SOD and POD were almost doubled under drought stress. The content of osmotic regulating substance proline and soluble sugar were three times than control group. But after re-watering, these indexes were declined rapidly. Three cDNA libraries of control, drought stress, and re-watering treatments were constructed. There were 43,129,228, 47,116,844, and 42,815,454 clean reads with Q20 values of 98.06, 98.04, and 97.88respectively.SRA accession number of raw data was PRJNA498187 on NCBI. A total of 8672, 6043, and 6537 differentially expressed genes (DEGs) were identified in control vs drought stress, control vs re-watering, and drought stress vs re-watering, respectively. In addition, 1039, 1016, and 980 transcription factors (TFs) were identified, respectively. Among them, 363, 267, and 299 TFs were identified as DEGs in drought stress, re-watering, and drought stress and re-watering, respectively. These differentially expressed TFs mainly belonged to the bHLH, bZIP, C2H2, ERF, MYB, MYB-related, and NAC families. A comparative analysis found that 1174 genes were up-regulated and 2344 were down-regulated under drought stress and this pattern was the opposite to that found after re-watering. Among the up-regulated genes, 64 genes were homologous to known functional genes that directly protect plants against drought stress. Furthermore, 44 protein kinases and 38 TFs with opposite expression patterns under drought stress and re-watering were identified, which are possibly candidate regulators for drought stress resistance in M. tenacissima. Our study is the first to characterize the M. tenacissima transcriptome in response to drought stress, and will serve as a useful resource for future studies on the functions of candidate protein kinases and TFs involved in M. tenacissima drought stress resistance.

New insights into the cellular mechanisms of plant growth at elevated atmospheric carbon dioxide concentrations

Rising atmospheric carbon dioxide concentration ([CO₂ ]) significantly influences plant growth, development, and biomass. Increased photosynthesis rate, together with lower stomatal conductance, has been identified as the key factors that stimulate plant growth at elevated [CO₂ ] (e[CO₂ ]). However, variations in photosynthesis and stomatal conductance alone cannot fully explain the dynamic changes in plant growth. Stimulation of photosynthesis at e[CO₂ ] is always associated with post-photosynthetic secondary metabolic processes that include carbon and nitrogen metabolism, cell cycle functions, and hormonal regulation. Most studies have focused on photosynthesis and stomatal conductance in response to e[CO₂ ], despite the emerging evidence of e[CO₂ ]'s role in moderating secondary metabolism in plants. In this review, we briefly discuss the effects of e[CO₂ ] on photosynthesis and stomatal conductance and then focus on the changes in other cellular mechanisms and growth processes at e[CO₂ ] in relation to plant growth and development. Finally, knowledge gaps in understanding plant growth responses to e[CO₂ ] have been identified with the aim of improving crop productivity under a CO₂ rich atmosphere.

Rice SUB1A constrains remodelling of the transcriptome and metabolome during submergence to facilitate post-submergence recovery

The rice (Oryza sativa L.) ethylene-responsive transcription factor gene SUB1A-1 confers tolerance to prolonged, complete submergence by limiting underwater elongation growth. Upon desubmergence, SUB1A-1 genotypes rapidly recover photosynthetic function and recommence development towards flowering. The underpinnings of the transition from stress amelioration to the return to homeostasis are not well known. Here, transcriptomic and metabolomic analyses were conducted to identify mechanisms by which SUB1A improves physiological function over the 24 hr following a sublethal submergence event. Evaluation of near-isogenic genotypes after submergence and over a day of reaeration demonstrated that SUB1A transiently constrains the remodelling of cellular activities associated with growth. SUB1A influenced the abundance of ca. 1,400 transcripts and had a continued impact on metabolite content, particularly free amino acids, glucose, and sucrose, throughout the recovery period. SUB1A promoted recovery of metabolic homeostasis but had limited influence on mRNAs associated with growth processes and photosynthesis. The involvement of low energy sensing during submergence and recovery was supported by dynamics in trehalose-6-phosphate and mRNAs encoding key enzymes and signalling proteins, which were modulated by SUB1A. This study provides new evidence of convergent signalling pathways critical to the rapidly reversible management of carbon and nitrogen metabolism in submergence resilient rice.

Characterization of the Symbiotic Nitrogen-Fixing Common Bean Low Phytic Acid (lpa1) Mutant Response to Water Stress

The common bean (Phaseolus vulgaris L.) low phytic acid (lpa1) biofortified genotype produces seeds with improved nutritional characteristics and does not display negative pleiotropic effects. Here we demonstrated that lpa1 plants establish an efficient nitrogen-fixing symbiosis with Rhizobium etli CE3. The lpa1 nodules showed a higher expression of nodule-function related genes than the nodules of the parental wild type genotype (BAT 93). We analyzed the response to water stress of lpa1 vs. BAT 93 plants grown under fertilized or under symbiotic N₂-fixation conditions. Water stress was induced by water withholding (up to 14% soil moisture) to fertilized or R. etli nodulated plants previously grown with normal irrigation. The fertilized lpa1 plants showed milder water stress symptoms during the water deployment period and after the rehydration recovery period when lpa1 plants showed less biomass reduction. The symbiotic water-stressed lpa1 plants showed decreased nitrogenase activity that coincides with decreased sucrose synthase gene expression in nodules; lower turgor weight to dry weight (DW) ratio, which has been associated with higher drought resistance index; downregulation of carbon/nitrogen (C/N)-related and upregulation of stress-related genes. Higher expression of stress-related genes was also observed in bacteroids of stressed lpa1 plants that also displayed very high expression of the symbiotic cbb₃ oxidase (fixNd).

Root lodging is a physical stress that changes gene expression from sucrose accumulation to degradation in sorghum

BACKGROUND

Sorghum (Sorghum bicolor L.) is used as a raw material for biofuels because it accumulates sugars at high levels in the stem. Lodging of sorghum occurs when the soil is wet and very high winds blow across the field. In root lodging, the roots are pulled loose from the soil, causing the plant to fall over. Lodging reduces the yield of nonstructural carbohydrates. It is not yet clear which genes show changes in expression when sorghum falls over. We compared whole-gene expression in the mature stems of intact and lodged sorghum plants, with a focus on comparisons from the perspective of differences in sugar accumulation or degradation.

RESULTS

Lodging decreased sucrose content, starch content, and ratio of sucrose to total sugars in the stems of the sorghum cultivar SIL-05. Particular paralogs of SWEET and TMT family genes, which encode sucrose or hexose transporters, or both, were significantly highly expressed in intact or lodged sorghum stems. In intact stems, genes encoding the glucose-6-phosphate translocator, aquaporins, and enzymes involved in photosynthesis and starch synthesis were highly expressed. In lodged sorghum stems, expression of genes associated with sucrose or starch degradation or energy production was increased. Notably, expression of genes encoding enzymes catalyzing irreversible reactions and associated with the first steps of these metabolic pathways (e.g. INV, SUS, and hexokinase- and fructokinase-encoding genes) was significantly increased by lodging. Expression of SUT, SPS, and SPP was almost the same in intact and lodged sorghum.

CONCLUSIONS

Specific paralogs of sucrose-associated genes involved in metabolic pathways and in membrane transport were expressed in the stems of sorghum SIL-05 at the full-ripe stage. Root lodging drastically changed the expression of these genes from sucrose accumulation to degradation. The changes in gene expression resulted in decreases in sugar content and in the proportion of sucrose to hexoses in the stems of lodged plants.

A Dual-Promoter Gene Orchestrates the Sucrose-Coordinated Synthesis of Starch and Fructan in Barley

Sequential carbohydrate synthesis is important for plant survival because it guarantees energy supplies for growth and development during plant ontogeny and reproduction. Starch and fructan are two important carbohydrates in many flowering plants and in human diets. Understanding this coordinated starch and fructan synthesis and unraveling how plants allocate photosynthates and prioritize different carbohydrate synthesis for survival could lead to improvements to cereals in agriculture for the purposes of greater food security and production quality. Here, we report a system from a single gene in barley employing two alternative promoters, one intronic/exonic, to generate two sequence-overlapping but functionally opposing transcription factors, in sensing sucrose, potentially via sucrose/glucose/fructose/trehalose 6-phosphate signaling. The system employs an autoregulatory mechanism in perceiving a sucrose-controlled trans activity on one promoter and orchestrating the coordinated starch and fructan synthesis by competitive transcription factor binding on the other promoter. As a case in point for the physiological roles of the system, we have demonstrated that this multitasking system can be exploited in breeding barley with tailored amounts of fructan to produce healthy food ingredients. The identification of an intron/exon-spanning promoter in a hosting gene, resulting in proteins with distinct functions, adds to the complexity of plant genomes.

Cloning and expression analysis of tps, and cryopreservation research of trehalose from Antarctic strain Pseudozyma sp

Trehalose is a non-reducing disaccharide sugar that widely exists in a variety of organisms, such as bacteria and eukaryotes except the vertebrates. It plays an important role in a number of critical metabolic functions especially in response to stressful environmental conditions. However, the biosynthetic pathways of trehalose in cold-adapted yeast and its responses to temperature and salinity changes remain little understood. In this study, the genome of Antarctic-isolated Pseudozyma sp. NJ7 was generated from which we identified the gene coding for trehalose phosphate synthase (TPS1) and trehalose phosphate phosphatase (TPS2), the two enzymes most critical for trehalose production. The whole draft genome length of Pseudozyma sp. NJ7 was 18,021,233 bp, and encoded at least 34 rRNA operons and 72 tRNAs. The open reading frame of tps1 contained 1827 nucleotide encoding 608 amino acids with a molecular weight of 67.64 kDa, and an isoelectric point of 5.54, while tps2 contained 3948 nucleotide encoding 1315 amino acids with a molecular weight of 144.47 kDa and an isoelectric point of 6.36. The TPS1 and TPS2 protein sequences were highly homologous to Moesziomyces antarcticus T-34, but TPS2 had obvious specificity and differently with others which suggest species specificity and different evolutionary history. Expression level of tps1 gene was strongly influenced by temperature and high salinity. In addition, addition of 0.5% trehalose preserved yeast cells in the short term but was not effective for cryopreservation for more than 5 days, but still suggesting that exogenous trehalose could indeed significantly improve the survival of yeast cells under freezing conditions. Our results provided new insights on the molecular basis of cold adaptations of Antarctic Pseudozyma sp., and also generated new information on the roles trehalose play in yeast tolerance to extreme conditions in the extreme Antarctic environments.

Metabolomic differential analysis of interspecific interactions among white rot fungi Trametes versicolor, Dichomitus squalens and Pleurotus ostreatus

Interspecific fungal antagonism occurred commonly in the interaction zone of different white rot fungi. This competitive interaction could markedly influence the metabolic pathway of intracellular metabolites, which was associated with the fungal morphology change and growth restriction. So far, it remains unknown on intracellular metabolite regulation during fungal competitive interaction. Herein, we performed the metabolomic analysis of the in vivo metabolite changes during competitive interaction between each two of the three white rot fungi Trametes versicolor, Pleurotus ostreatus and Dichomitus squalens and identified differential metabolites in the interaction zone compared to each two isolates. Many metabolites in the carnitine, lipid, ethylene and trehalose metabolic pathways were significantly up-regulated. These metabolic pathways are all involved in defensive response to abiotic and/or biotic stressful condition.

The role of Tre6P and SnRK1 in maize early kernel development and events leading to stress-induced kernel abortion

BACKGROUND

Drought stress during flowering is a major contributor to yield loss in maize. Genetic and biotechnological improvement in yield sustainability requires an understanding of the mechanisms underpinning yield loss. Sucrose starvation has been proposed as the cause for kernel abortion; however, potential targets for genetic improvement have not been identified. Field and greenhouse drought studies with maize are expensive and it can be difficult to reproduce results; therefore, an in vitro kernel culture method is presented as a proxy for drought stress occurring at the time of flowering in maize (3 days after pollination). This method is used to focus on the effects of drought on kernel metabolism, and the role of trehalose 6-phosphate (Tre6P) and the sucrose non-fermenting-1-related kinase (SnRK1) as potential regulators of this response.

RESULTS

A precipitous drop in Tre6P is observed during the first two hours after removing the kernels from the plant, and the resulting changes in transcript abundance are indicative of an activation of SnRK1, and an immediate shift from anabolism to catabolism. Once Tre6P levels are depleted to below 1 nmol∙g-1 FW in the kernel, SnRK1 remained active throughout the 96 h experiment, regardless of the presence or absence of sucrose in the medium. Recovery on sucrose enriched medium results in the restoration of sucrose synthesis and glycolysis. Biosynthetic processes including the citric acid cycle and protein and starch synthesis are inhibited by excision, and do not recover even after the re-addition of sucrose. It is also observed that excision induces the transcription of the sugar transporters SUT1 and SWEET1, the sucrose hydrolyzing enzymes CELL WALL INVERTASE 2 (INCW2) and SUCROSE SYNTHASE 1 (SUSY1), the class II TREHALOSE PHOSPHATE SYNTHASES (TPS), TREHALASE (TRE), and TREHALOSE PHOSPHATE PHOSPHATASE (ZmTPPA.3), previously shown to enhance drought tolerance (Nuccio et al., Nat Biotechnol (October 2014):1-13, 2015).

CONCLUSIONS

The impact of kernel excision from the ear triggers a cascade of events starting with the precipitous drop in Tre6P levels. It is proposed that the removal of Tre6P suppression of SnRK1 activity results in transcription of putative SnRK1 target genes, and the metabolic transition from biosynthesis to catabolism. This highlights the importance of Tre6P in the metabolic response to starvation. We also present evidence that sugars can mediate the activation of SnRK1. The precipitous drop in Tre6P corresponds to a large increase in transcription of ZmTPPA.3, indicating that this specific enzyme may be responsible for the de-phosphorylation of Tre6P. The high levels of Tre6P in the immature embryo are likely important for preventing kernel abortion.

New Insights on Drought Stress Response by Global Investigation of Gene Expression Changes in Sheepgrass (Leymus chinensis)

Water is a critical environmental factor that restricts the geographic distribution of plants. Sheepgrass [Leymus chinensis, (Trin.) Tzvel] is an important forage grass in the Eurasia Steppe and a close germplasm for wheat and barley. This native grass adapts well to adverse environments such as cold, salinity, alkalinity and drought, and it can survive when the soil moisture may be less than 6% in dry seasons. However, little is known about how sheepgrass tolerates water stress at the molecular level. Here, drought stress experiment and RNA-sequencing (RNA-seq) was performed in three pools of RNA samples (control, drought stress, and rewatering). We found that sheepgrass seedlings could still survive when the soil water content (SWC) was reduced to 14.09%. Differentially expressed genes (DEGs) analysis showed that 7320 genes exhibited significant responses to drought stress. Of these DEGs, 2671 presented opposite expression trends before and after rewatering. Furthermore, ~680 putative sheepgrass-specific water responsive genes were revealed that can be studied deeply. Gene ontology (GO) annotation revealed that stress-associated genes were activated extensively by drought treatment. Interestingly, cold stress-related genes were up-regulated greatly after drought stress. The DEGs of MAPK and calcium signal pathways, plant hormone ABA, jasmonate, ethylene, brassinosteroid signal pathways, cold response CBF pathway participated coordinatively in sheepgrass drought stress response. In addition, we identified 288 putative transcription factors (TFs) involved in drought response, among them, the WRKY, NAC, AP2/ERF, bHLH, bZIP, and MYB families were enriched, and might play crucial and significant roles in drought stress response of sheepgrass. Our research provided new and valuable information for understanding the mechanism of drought tolerance in sheepgrass. Moreover, the identification of genes involved in drought response can facilitate the genetic improvement of crops by molecular breeding.

Transcription Profiles Reveal Sugar and Hormone Signaling Pathways Mediating Flower Induction in Apple (Malus domestica Borkh.)

Flower induction in apple (Malus domestica Borkh.) is regulated by complex gene networks that involve multiple signal pathways to ensure flower bud formation in the next year, but the molecular determinants of apple flower induction are still unknown. In this research, transcriptomic profiles from differentiating buds allowed us to identify genes potentially involved in signaling pathways that mediate the regulatory mechanisms of flower induction. A hypothetical model for this regulatory mechanism was obtained by analysis of the available transcriptomic data, suggesting that sugar-, hormone- and flowering-related genes, as well as those involved in cell-cycle induction, participated in the apple flower induction process. Sugar levels and metabolism-related gene expression profiles revealed that sucrose is the initiation signal in flower induction. Complex hormone regulatory networks involved in cytokinin (CK), abscisic acid (ABA) and gibberellic acid pathways also induce apple flower formation. CK plays a key role in the regulation of cell formation and differentiation, and in affecting flowering-related gene expression levels during these processes. Meanwhile, ABA levels and ABA-related gene expression levels gradually increased, as did those of sugar metabolism-related genes, in developing buds, indicating that ABA signals regulate apple flower induction by participating in the sugar-mediated flowering pathway. Furthermore, changes in sugar and starch deposition levels in buds can be affected by ABA content and the expression of the genes involved in the ABA signaling pathway. Thus, multiple pathways, which are mainly mediated by crosstalk between sugar and hormone signals, regulate the molecular network involved in bud growth and flower induction in apple trees.

Impact of concurrent overexpression of cytosolic glutamine synthetase (GS1) and sucrose phosphate synthase (SPS) on growth and development in transgenic tobacco

MAIN CONCLUSION

The outcome of simultaneously increasing SPS and GS activities in transgenic tobacco, suggests that sucrose is the major determinant of growth and development, and is not affected by changes in N assimilation. Carbon (C) and nitrogen (N) are the major components required for plant growth and the metabolic pathways for C and N assimilation are very closely interlinked. Maintaining an appropriate balance or ratio of sugar to nitrogen metabolites in the cell, is important for the regulation of plant growth and development. To understand how C and N metabolism interact, we manipulated the expression of key genes in C and N metabolism individually and concurrently and checked for the repercussions. Transgenic tobacco plants with a cytosolic soybean glutamine synthetase (GS1) gene and a sucrose phosphate synthase (SPS) gene from maize, both driven by the CaMV 35S promoter were produced. Co-transformants, with both the transgenes were produced by sexual crosses. While GS is the key enzyme in N assimilation, involved in the synthesis of glutamine, SPS plays a key role in C metabolism by catalyzing the synthesis of sucrose. Moreover, to check if nitrate has any role in this interaction, the plants were grown under both low and high nitrogen. The SPS enzyme activity in the SPS and SPS/GS1 co-transformants were the same under both nitrogen regimens. However, the GS activity was lower in the co-transformants compared to the GS1 transformants, specifically under low nitrogen conditions. The GS1/SPS transformants showed a phenotype similar to the SPS transformants, suggesting that sucrose is the major determinant of growth and development in tobacco, and its effect is only marginally affected by increased N assimilation. Sucrose may be functioning in a metabolic capacity or as a signaling molecule.

The trehalose pathway in maize: conservation and gene regulation in response to the diurnal cycle and extended darkness

Energy resources in plants are managed in continuously changing environments, such as changes occurring during the day/night cycle. Shading is an environmental disruption that decreases photosynthesis, compromises energy status, and impacts on crop productivity. The trehalose pathway plays a central but not well-defined role in maintaining energy balance. Here, we characterized the maize trehalose pathway genes and deciphered the impacts of the diurnal cycle and disruption of the day/night cycle on trehalose pathway gene expression and sugar metabolism. The maize genome encodes 14 trehalose-6-phosphate synthase (TPS) genes, 11 trehalose-6-phosphate phosphatase (TPP) genes, and one trehalase gene. Transcript abundance of most of these genes was impacted by the day/night cycle and extended dark stress, as were sucrose, hexose sugars, starch, and trehalose-6-phosphate (T6P) levels. After extended darkness, T6P levels inversely followed class II TPS and sucrose non-fermenting-related protein kinase 1 (SnRK1) target gene expression. Most significantly, T6P no longer tracked sucrose levels after extended darkness. These results showed: (i) conservation of the trehalose pathway in maize; (ii) that sucrose, hexose, starch, T6P, and TPS/TPP transcripts respond to the diurnal cycle; and(iii) that extended darkness disrupts the correlation between T6P and sucrose/hexose pools and affects SnRK1 target gene expression. A model for the role of the trehalose pathway in sensing of sucrose and energy status in maize seedlings is proposed.

Comprehensive transcriptome analysis unravels the existence of crucial genes regulating primary metabolism during adventitious root formation in Petunia hybrida

To identify specific genes determining the initiation and formation of adventitious roots (AR), a microarray-based transcriptome analysis in the stem base of the cuttings of Petunia hybrida (line W115) was conducted. A microarray carrying 24,816 unique, non-redundant annotated sequences was hybridized to probes derived from different stages of AR formation. After exclusion of wound-responsive and root-regulated genes, 1,354 of them were identified which were significantly and specifically induced during various phases of AR formation. Based on a recent physiological model distinguishing three metabolic phases in AR formation, the present paper focuses on the response of genes related to particular metabolic pathways. Key genes involved in primary carbohydrate metabolism such as those mediating apoplastic sucrose unloading were induced at the early sink establishment phase of AR formation. Transcriptome changes also pointed to a possible role of trehalose metabolism and SnRK1 (sucrose non-fermenting 1- related protein kinase) in sugar sensing during this early step of AR formation. Symplastic sucrose unloading and nucleotide biosynthesis were the major processes induced during the later recovery and maintenance phases. Moreover, transcripts involved in peroxisomal beta-oxidation were up-regulated during different phases of AR formation. In addition to metabolic pathways, the analysis revealed the activation of cell division at the two later phases and in particular the induction of G1-specific genes in the maintenance phase. Furthermore, results point towards a specific demand for certain mineral nutrients starting in the recovery phase.

The improved resistance to high salinity induced by trehalose is associated with ionic regulation and osmotic adjustment in Catharanthus roseus

The effects of exogenous trehalose (Tre) on salt tolerance of pharmaceutical plant Catharanthus roseus and the physiological mechanisms were both investigated in this study. The results showed that the supplement of Tre in saline condition (250 mM NaCl) largely alleviated the inhibitory effects of salinity on plant growth, namely biomass accumulation and total leaf area per plant. In this saline condition, the decreased level of relative water content (RWC) and photosynthetic rate were also greatly rescued by exogenous Tre. This improved performance of plants under high salinity induced by Tre could be partly ascribed to its ability to decrease accumulation of sodium, and increase potassium in leaves. The exogenous Tre led to high levels of fructose, glucose, sucrose and Tre inside the salt-stressed plants during whole the three-week treatment. The major free amino acids such as proline, arginine, threonine and glutamate were also largely elevated in the first two-week course of treatment with Tre in saline solution. It was proposed here that Tre might act as signal to make the salt-stressed plants actively increase internal compatible solutes, including soluble sugars and free amino acids, to control water loss, leaf gas exchange and ionic flow at the onset of salt stress. The application of Tre in saline condition also promoted the accumulation of alkaloids. The regulatory role of Tre in improving salt tolerance was optimal with an exogenous concentration of 10 mM Tre. Larger concentrations of Tre were supra-optimum and adversely affected plant growth.

Substantial roles of hexokinase and fructokinase in the effects of sugars on plant physiology and development

The basic requirements for plant growth are light, CO2, water, and minerals. However, the absorption and utilization of each of these requires investment on the part of the plant. The primary products of plants are sugars, and the hexose sugars glucose and fructose are the raw material for most of the metabolic pathways and organic matter in plants. To be metabolized, hexose sugars must first be phosphorylated. Only two families of enzymes capable of catalysing the essential irreversible phosphorylation of glucose and fructose have been identified in plants, hexokinases (HXKs) and fructokinases (FRKs). These hexose-phosphorylating enzymes appear to coordinate sugar production with the abilities to absorb light, CO2, water, and minerals. This review describes the long- and short-term effects mediated by HXK and FRK in various tissues, as well as the role of these enzymes in the coordination of sugar production with the absorption of light, CO2, water, and minerals.

Systematic screening for novel lipids by shotgun lipidomics

A commonly accepted LIPID MAPS classification recognizes eight major lipid categories and over 550 classes, while new lipid classes are still being discovered by targeted biochemical approaches. Despite their compositional diversity, complex lipids such as glycerolipids, glycerophospholipids, saccharolipids, etc. are constructed from unique structural moieties, e.g., glycerol, fatty acids, choline, phosphate, and trehalose, that are linked by amide, ether, ester, or glycosidic bonds. This modular organization is also reflected in their MS/MS fragmentation pathways, such that common building blocks in different lipid classes tend to generate common fragments. We take advantage of this stereotyped fragmentation to systematically screen for new lipids sharing distant structural similarity to known lipid classes and have developed a discovery approach based on the computational querying of shotgun mass spectra by LipidXplorer software. We applied this concept for screening lipid extracts of C. elegans larvae at the dauer and L3 stages that represent alternative developmental programs executed in response to environmental challenges. The search, covering more than 1.5 million putative chemical compositions, identified a novel class of lyso-maradolipids specifically enriched in dauer larvae.

Regulation of potato tuber sprouting

Following tuber induction, potato tubers undergo a period of dormancy during which visible bud growth is inhibited. The length of the dormancy period is under environmental, physiological and hormonal control. Sucrose availability is one prerequisite for bud break. In the absence of sucrose, no bud break occurs. Thus, sucrose is likely to serve as nutrient and signal molecule at the same time. The mode of sucrose sensing is only vaguely understood, but most likely involves trehalose-6-phosphate and SnRK1 signalling networks. This conclusion is supported by the observation that ectopically manipulation of trehalose-6-phosphate levels influences the length of the dormancy period. Once physiological competence is achieved, sprouting is controlled by the level of phytohormones. Two phytohormones, ABA and ethylene, are supposed to suppress tuber sprouting; however, the exact role of ethylene remains to be elucidated. Cytokinins and gibberellins are required for bud break and sprout growth, respectively. The fifth classical phytohormone, auxin, seems to play a role in vascular development. During the dormancy period, buds are symplastically isolated, which changes during bud break. In parallel to the establishment of symplastic connectivity, vascular tissue develops below the growing bud most likely to support the outgrowing sprout with assimilates mobilised in parenchyma cells. Sprouting leads to major quality losses of stored potato tubers. Therefore, control of tuber sprouting is a major objective in potato breeding. Although comparative transcriptome analysis revealed a large number of genes differentially expressed in growing versus dormant buds, no master-regulator of potato tuber sprouting has been identified so far.

Source/sink interactions underpin crop yield: the case for trehalose 6-phosphate/SnRK1 in improvement of wheat

Considerable interest has been evoked by the analysis of the regulatory pathway in carbohydrate metabolism and cell growth involving the non-reducing disaccharide trehalose (TRE). TRE is at small concentrations in mesophytes such as Arabidopsis thaliana and Triticum aestivum, excluding a role in osmoregulation once suggested for it. Studies of TRE metabolism, and genetic modification of it, have shown a very wide and more important role of the pathway in regulation of many processes in development, growth, and photosynthesis. It has now been established that rather than TRE, it is trehalose 6-phosphate (T6P) which has such profound effects. T6P is the intermediary in TRE synthesis formed from glucose-6-phosphate and UDP-glucose, derived from sucrose, by the action of trehalose phosphate synthase. The concentration of T6P is determined both by the rate of synthesis, which depends on the sucrose concentration, and also by the rate of breakdown by trehalose-6-phosphate phosphatase which produces TRE. Changing T6P concentrations by genetically modifying the enzymes of synthesis and breakdown has altered photosynthesis, sugar metabolism, growth, and development which affect responses to, and recovery from, environmental factors. Many of the effects of T6P on metabolism and growth occur via the interaction of T6P with the SnRK1 protein kinase system. T6P inhibits the activity of SnRK1, which de-represses genes encoding proteins involved in anabolism. Consequently, a large concentration of sucrose increases T6P and thereby inhibits SnRK1, so stimulating growth of cells and their metabolic activity. The T6P/SnRK1 mechanism offers an important new view of how the distribution of assimilates to organs, such as developing grains in cereal plants, is achieved. This review briefly summarizes the factors determining, and limiting, yield of wheat (particularly mass/grain which is highly conserved) and considers how T6P/SnRK1 might function to determine grain yield and might be altered to increase them. Increasing the potential rate of filling and mass/grain are ways in which total crop yield could be increased with good husbandry which maintains crop assimilation Cereal yields globally are not increasing, despite the greater production required to meet human demand. Careful targeting of T6P is showing much promise for optimization of source/sink for yield improvement and offers yet further possibilities for increasing sink demand and grain size in wheat.