The signal metabolite trehalose-6-phosphate inhibits the sucrolytic activity of sucrose synthase from developing castor beans

Study on the physiological mechanism and transcriptional regulatory network of early fruit development in Gleditsia sinensis Lam. (Fabaceae)

BACKGROUND

Gleditsia sinensis Lam. (Fabaceae) is a medicinal legume characterized by its spines and pods, which are rich in saponins, polysaccharides, and various specialized metabolites with potential medicinal and industrial applications. The low fruit set rate in artificially cultivated economic forests significantly impedes its development and utilization. A comprehensive understanding of the cellular events, physiological and biochemical processes, and molecular regulatory mechanisms underlying fruit initiation and early fruit development is essential for enhancing yield. However, such information for G. sinensis remains largely unexplored.

RESULTS

In this study, we identified that the early fruit development process in G. sinensis can be categorized into three distinct stages: pollination, the critical period of fertilization, and the initial fruit development followed by subsequent growth. The dynamic changes in non-structural carbohydrates and endogenous plant hormones within the ovary were found to play a significant role during fruit set and the early stages of fruit development. Additionally, the high activity of gibberellin, cytokinin, and sucrose-metabolizing enzymes in the ovary was conducive to early fruit development. Furthermore, we generated high-resolution spatiotemporal gene expression profiles in the ovary from the stage of efflorescence to early fruit development. Comparative transcriptomics and weighted gene co-expression network analysis revealed specific genes and gene modules predominant at distinct developmental stages, thereby highlighting unique genetic programming. Overall, we identified the potential regulatory network governing fruit initiation and subsequent development, as well as the sets of candidate genes involved, based on the aforementioned results.

CONCLUSIONS

The results offer a valuable reference and resource for the application of exogenous substances, such as hormones and sugars, during critical fruit development periods, and for the development of molecular tools aimed at improving yield.

Direct and indirect responses of the Arabidopsis transcriptome to an induced increase in trehalose 6-phosphate

Trehalose 6-phosphate (Tre6P) is an essential signal metabolite that regulates the level of sucrose, linking growth and development to the metabolic status. We hypothesized that Tre6P plays a role in mediating the regulation of gene expression by sucrose. To test this, we performed transcriptomic profiling on Arabidopsis (Arabidopsis thaliana) plants that expressed a bacterial TREHALOSE 6-PHOSPHATE SYNTHASE (TPS) under the control of an ethanol-inducible promoter. Induction led to a 4-fold rise in Tre6P levels, a concomitant decrease in sucrose, significant changes (FDR ≤ 0.05) of over 13,000 transcripts, and 2-fold or larger changes of over 5,000 transcripts. Comparison with nine published responses to sugar availability allowed some of these changes to be linked to the rise in Tre6P, while others were probably due to lower sucrose or other indirect effects. Changes linked to Tre6P included repression of photosynthesis-related gene expression and induction of many growth-related processes including ribosome biogenesis. About 500 starvation-related genes are known to be induced by SUCROSE-NON-FERMENTING-1-RELATED KINASE 1 (SnRK1). They were largely repressed by Tre6P in a manner consistent with SnRK1 inhibition by Tre6P. SnRK1 also represses many genes that are involved in biosynthesis and growth. These responded to Tre6P in a more complex manner, pointing toward Tre6P interacting with other C-signaling pathways. Additionally, elevated Tre6P modified the expression of genes encoding regulatory subunits of the SnRK1 complex and TPS class II and FCS-LIKE ZINC FINGER proteins that are thought to modulate SnRK1 function and genes involved in circadian, TARGET OF RAPAMYCIN, light, abscisic acid, and other hormone signaling.

Uncovering the complex regulatory network of spring bud sprouting in tea plants: insights from metabolic, hormonal, and oxidative stress pathways

The sprouting process of tea buds is an essential determinant of tea quality and taste, thus profoundly impacting the tea industry. Buds spring sprouting is also a crucial biological process adapting to external environment for tea plants and regulated by complex transcriptional and metabolic networks. This study aimed to investigate the molecular basis of bud sprouting in tea plants firstly based on the comparisons of metabolic and transcriptional profiles of buds at different developmental stages. Results notably highlighted several essential processes involved in bud sprouting regulation, including the interaction of plant hormones, glucose metabolism, and reactive oxygen species scavenging. Particularly prior to bud sprouting, the accumulation of soluble sugar reserves and moderate oxidative stress may have served as crucial components facilitating the transition from dormancy to active growth in buds. Following the onset of sprouting, zeatin served as the central component in a multifaceted regulatory mechanism of plant hormones that activates a range of growth-related factors, ultimately leading to the promotion of bud growth. This process was accompanied by significant carbohydrate consumption. Moreover, related key genes and metabolites were further verified during the entire overwintering bud development or sprouting processes. A schematic diagram involving the regulatory mechanism of bud sprouting was ultimately proposed, which provides fundamental insights into the complex interactions involved in tea buds.

Metabolic regulation of quiescence in plants

Quiescence is a crucial survival attribute in which cell division is repressed in a reversible manner. Although quiescence has long been viewed as an inactive state, recent studies have shown that it is an actively monitored process that is influenced by environmental stimuli. Here, we provide a perspective of the quiescent state and discuss how this process is tuned by energy, nutrient and oxygen status, and the pathways that sense and transmit these signals. We not only highlight the governance of canonical regulators and signalling mechanisms that respond to changes in nutrient and energy status, but also consider the central significance of mitochondrial functions and cues as key regulators of nuclear gene expression. Furthermore, we discuss how reactive oxygen species and the associated redox processes, which are intrinsically linked to energy carbohydrate metabolism, also play a key role in the orchestration of quiescence.

Photosynthetic acclimation to changing environments

Plants are exposed to environments that fluctuate of timescales varying from seconds to months. Leaves that develop in one set of conditions optimise their metabolism to the conditions experienced, in a process called developmental acclimation. However, when plants experience a sustained change in conditions, existing leaves will also acclimate dynamically to the new conditions. Typically this process takes several days. In this review, we discuss this dynamic acclimation process, focussing on the responses of the photosynthetic apparatus to light and temperature. We briefly discuss the principal changes occurring in the chloroplast, before examining what is known, and not known, about the sensing and signalling processes that underlie acclimation, identifying likely regulators of acclimation.

Imperative role of trehalose metabolism and trehalose-6-phosphate signaling on salt stress responses in plants

Sugar transport and distribution have a direct impact on the growth and development of plants. Many sugars significantly influence salt stress response. The sensing of salt stress signals triggers a wide array of complicated network transduction pathways in plants. Trehalose and its intermediate compounds effectively modulate salt response and salt tolerance. Sugars such as trehalose and its derivatives not only serve as metabolic resources and structural components of cells in plants but also exhibit hormone-like regulating properties. Trehalose has an important physiological role in improving plant tolerance against salinity stresses in different plants. Plants finely adjust their cytoplasmic compatible solute pool to cope with high salinity. Salt stress induces a variety of structural, anatomical, molecular, biochemical, and physiological changes in plants, all of which have a detrimental influence on plant growth and development. This review highlights the recent developments in understanding trehalose and trehalose-6-phosphate signaling processes in plants, especially their impacts on plants growing in salty environments.

Overdominance at the Gene Expression Level Plays a Critical Role in the Hybrid Root Growth of Brassica napus

Despite heterosis contributing to genetic improvements in crops, root growth heterosis in rapeseed plants is poorly understood at the molecular level. The current study was performed to discover key differentially expressed genes (DEGs) related to heterosis in two hybrids with contrasting root growth performance (FO; high hybrid and FV; low hybrid) based on analysis of the root heterosis effect. Based on comparative transcriptomic analysis, we believe that the overdominance at the gene expression level plays a critical role in hybrid roots’ early biomass heterosis. Our findings imply that a considerable increase in up-regulation of gene expression underpins heterosis. In the FO hybrid, high expression of DEGs overdominant in the starch/sucrose and galactose metabolic pathways revealed a link between hybrid vigor and root growth. DEGs linked to auxin, cytokinin, brassinosteroids, ethylene, and abscisic acid were also specified, showing that these hormones may enhance mechanisms of root growth and the development in the FO hybrid. Moreover, transcription factors such as MYB, ERF, bHLH, NAC, bZIP, and WRKY are thought to control downstream genes involved in root growth. Overall, this is the first study to provide a better understanding related to the regulation of the molecular mechanism of heterosis, which assists in rapeseed growth and yield improvement.

Understanding Starch Metabolism in Pea Seeds towards Tailoring Functionality for Value-Added Utilization

Starch is the most abundant storage carbohydrate and a major component in pea seeds, accounting for about 50% of dry seed weight. As a by-product of pea protein processing, current uses for pea starch are limited to low-value, commodity markets. The globally growing demand for pea protein poses a great challenge for the pea fractionation industry to develop new markets for starch valorization. However, there exist gaps in our understanding of the genetic mechanism underlying starch metabolism, and its relationship with physicochemical and functional properties, which is a prerequisite for targeted tailoring functionality and innovative applications of starch. This review outlines the understanding of starch metabolism with a particular focus on peas and highlights the knowledge of pea starch granule structure and its relationship with functional properties, and industrial applications. Using the currently available pea genetics and genomics knowledge and breakthroughs in omics technologies, we discuss the perspectives and possible avenues to advance our understanding of starch metabolism in peas at an unprecedented level, to ultimately enable the molecular design of multi-functional native pea starch and to create value-added utilization.

Non-structural carbohydrates coordinate tree peony flowering both as energy substrates and as sugar signaling triggers, with the bracts playing an essential role

The natural fluorescence of tree peony is short. Forcing culture, mainly by defoliation and gibberellin (GA) treatment, is frequently used for its industrial production. We previously found forcing culture to be coordinated by non-structural carbohydrates (NSCs). Herein, we further revealed the specific role of NSCs during this process. We observed that both defoliation and GA treatment increased the photosynthesis in the bracts, and defoliation had a greater effect on NSC assimilation. We further determined the NSC content and PsSWEETs expression in the bracts, and the results indicated that GA may contribute more to NSC allocation by inducing PsSWEET7. Furthermore, we determined the trehalose-6-phosphate (T6P) content and sugar signaling-related gene (PsTPS1, PsSnRK1, and PsHXK1) expression in both the petals and bracts and found that both defoliation and GA treatment induced T6P levels as well as PsTPS1 expression in both tissues. This indicated that the sugar signaling pathway may also be involved in NSC-coordinated tree peony flowering. In particular, PsSnRK1 was more rapidly induced in the bracts (as an energy shortage response) in the control plants and was completely prohibited by defoliation and GA treatment, indicating the key role of the bracts in sugar signaling. In conclusion, NSCs induced tree peony flowering both as an energy substrate and sugar signaling trigger, with the bracts playing an essential role. These results may provide further evidence on the mechanism of NSC-coordinated flower opening in tree peony under forcing culture conditions, which may also provide a foundation for improving this technology.

Metabolic engineering of osmoprotectants to elucidate the mechanism(s) of salt stress tolerance in crop plants

Previous studies on engineering osmoprotectant metabolic pathway genes focused on the performance of transgenic plants under salt stress conditions rather than elucidating the underlying mechanism(s), and hence, the mechanism(s) remain(s) unclear. Salt stress negatively impacts agricultural crop yields. Hence, to meet future food demands, it is essential to generate salt stress-resistant varieties. Although traditional breeding has improved salt tolerance in several crops, this approach remains inadequate due to the low genetic diversity of certain important crop cultivars. Genetic engineering is used to introduce preferred gene(s) from any genetic reserve or to modify the expression of the existing gene(s) responsible for salt stress response or tolerance, thereby leading to improved salt tolerance in plants. Although plants naturally produce osmoprotectants as an adaptive mechanism for salt stress tolerance, they offer only partial protection. Recently, progress has been made in the identification and characterization of genes involved in the biosynthetic pathways of osmoprotectants. Exogenous application of these osmoprotectants, and genetic engineering of enzymes in their biosynthetic pathways, have been reported to enhance salt tolerance in different plants. However, no clear mechanistic model exists to explain how osmoprotectant accumulation in transgenic plants confers salt tolerance. This review critically examines the results obtained thus far for elucidating the underlying mechanisms of osmoprotectants for improved salt tolerance, and thus, crop yield stability under salt stress conditions, through the genetic engineering of trehalose, glycinebetaine, and proline metabolic pathway genes.

Multifaceted functions of post-translational enzyme modifications in the control of plant glycolysis

Glycolysis is a central feature of metabolism and its regulation plays important roles during plant developmental and stress responses. Recent advances in proteomics and mass spectrometry have documented extensive and dynamic post-translational modifications (PTMs) of most glycolytic enzymes in diverse plant tissues. Protein PTMs represent fundamental regulatory events that integrate signalling and gene expression with cellular metabolic networks, and can regulate glycolytic enzyme activity, localization, protein:protein interactions, moonlighting functions, and turnover. Serine/threonine phosphorylation and redox PTMs of cysteine thiol groups appear to be the most prevalent forms of reversible covalent modification involved in plant glycolytic control. Additional PTMs including monoubiquitination also have important functions. However, the molecular functions and mechanisms of most glycolytic enzyme PTMs remain unknown, and represent important objectives for future studies.

Transcriptome profiling of non-climacteric 'yellow' melon during ripening: insights on sugar metabolism

BACKGROUND

The non-climacteric 'Yellow' melon (Cucumis melo, inodorus group) is an economically important crop and its quality is mainly determined by the sugar content. Thus, knowledge of sugar metabolism and its related pathways can contribute to the development of new field management and post-harvest practices, making it possible to deliver better quality fruits to consumers.

RESULTS

The RNA-seq associated with RT-qPCR analyses of four maturation stages were performed to identify important enzymes and pathways that are involved in the ripening profile of non-climacteric 'Yellow' melon fruit focusing on sugar metabolism. We identified 895 genes 10 days after pollination (DAP)-biased and 909 genes 40 DAP-biased. The KEGG pathway enrichment analysis of these differentially expressed (DE) genes revealed that 'hormone signal transduction', 'carbon metabolism', 'sucrose metabolism', 'protein processing in endoplasmic reticulum' and 'spliceosome' were the most differentially regulated processes occurring during melon development. In the sucrose metabolism, five DE genes are up-regulated and 12 are down-regulated during fruit ripening.

CONCLUSIONS

The results demonstrated important enzymes in the sugar pathway that are responsible for the sucrose content and maturation profile in non-climacteric 'Yellow' melon. New DE genes were first detected for melon in this study such as invertase inhibitor LIKE 3 (CmINH3), trehalose phosphate phosphatase (CmTPP1) and trehalose phosphate synthases (CmTPS5, CmTPS7, CmTPS9). Furthermore, the results of the protein-protein network interaction demonstrated general characteristics of the transcriptome of young and full-ripe melon and provide new perspectives for the understanding of ripening.

Functional Characterization of Class I Trehalose Biosynthesis Genes in Physcomitrella patens

The function of trehalose metabolism in plants during growth and development has been extensively studied, mostly in the eudicot Arabidopsis thaliana. So far, however, not much is known about trehalose metabolism in the moss Physcomitrella patens. Here, we show that in P. patens, two active trehalose-6-phosphate synthase enzymes exist, PpTPS1 and PpTPS2. Expression of both enzymes in Saccharomyces cerevisiae can complement the glucose-growth defect of the yeast tps1∆ mutant. Truncation of N-terminal extension in PpTPS1 and PpTPS2 resulted in higher TPS activity and high trehalose levels, upon expression in yeast. Physcomitrella knockout plants were generated and analyzed in various conditions to functionally characterize these proteins. tps1∆ and tps2∆ knockouts displayed a lower amount of caulonema filaments and were significantly reduced in size of gametophores as compared to the wild type. These phenotypes were more pronounced in the tps1∆ tps2∆ mutant. Caulonema formation is induced by factors such as high energy and auxins. Only high amounts of supplied energy were able to induce caulonema filaments in the tps1∆ tps2∆ mutant. Furthermore, this mutant was less sensitive to auxins as NAA-induced caulonema development was arrested in the tps1∆ tps2∆ mutant. In contrast, formation of caulonema filaments is repressed by cytokinins. This effect was more severe in the tps1∆ and tps1∆ tps2∆ mutants. Our results demonstrate that PpTPS1 and PpTPS2 are essential for sensing and signaling sugars and plant hormones to monitor the balance between caulonema and chloronema development.

Piperidine carbamate peptidomimetic inhibitors of the serine proteases HGFA, matriptase and hepsin

Matriptase and hepsin are type II transmembrane serine proteases (TTSPs). Along with related S1 trypsin like serine protease HGFA (hepatocyte growth factor activator), their unregulated proteolytic activity has been associated with cancer including tumor progression and metastasis. These three proteases have two substrates in common, hepatocyte growth factor (HGF) and macrophage stimulating protein (MSP), the ligands for MET and recepteur d'origine nantais (RON) receptor tyrosine kinases. Mechanism-based tetrapeptide and benzamidine inhibitors of these proteases have been shown to block HGF/MET and MSP/RON cancer cell signaling. Herein, we have rationally designed a new class of peptidomimetic hybrid small molecule piperidine carbamate dipeptide inhibitors comparable in potency to much larger tetrapeptides. We have identified multiple compounds which have potent activity against matriptase and hepsin and with excellent selectivity over the off-target serine proteases factor Xa and thrombin.

An Overview of Sucrose Synthases in Plants

Sucrose is the end product of photosynthesis and the primary sugar transported in the phloem of most plants. Sucrose synthase (SuSy) is a glycosyl transferase enzyme that plays a key role in sugar metabolism, primarily in sink tissues. SuSy catalyzes the reversible cleavage of sucrose into fructose and either uridine diphosphate glucose (UDP-G) or adenosine diphosphate glucose (ADP-G). The products of sucrose cleavage by SuSy are available for many metabolic pathways, such as energy production, primary-metabolite production, and the synthesis of complex carbohydrates. SuSy proteins are usually homotetramers with an average monomeric molecular weight of about 90 kD (about 800 amino acids long). Plant SuSy isozymes are mainly located in the cytosol or adjacent to plasma membrane, but some SuSy proteins are found in the cell wall, vacuoles, and mitochondria. Plant SUS gene families are usually small, containing between four to seven genes, with distinct exon-intron structures. Plant SUS genes are divided into three separate clades, which are present in both monocots and dicots. A comprehensive phylogenetic analysis indicates that a first SUS duplication event may have occurred before the divergence of the gymnosperms and angiosperms and a second duplication event probably occurred in a common angiosperm ancestor, leading to the existence of all three clades in both monocots and dicots. Plants with reduced SuSy activity have been shown to have reduced growth, reduced starch, cellulose or callose synthesis, reduced tolerance to anaerobic-stress conditions and altered shoot apical meristem function and leaf morphology. Plants overexpressing SUS have shown increased growth, increased xylem area and xylem cell-wall width, and increased cellulose and starch contents, making SUS high-potential candidate genes for the improvement of agricultural traits in crop plants. This review summarizes the current knowledge regarding plant SuSy, including newly discovered possible developmental roles for SuSy in meristem functioning that involve sugar and hormonal signaling.