Interaction between sugar transport and plant development

How vacuolar sugar transporters evolve and control cellular sugar homeostasis, organ development and crop yield

Sugar exchange among different subcellular compartments is central for achieving cellular sugar homeostasis and directly affects the yield and quality of many horticultural and field crops. While a portion of photosynthesis-originated sugars is metabolized through glycolysis upon entering the cytosol, the remainder is reversibly channelled to the vacuole, mediated by different families of vacuolar sugar transporter (VST) located on the vacuolar membrane, the tonoplast. Historically, sugar transporters operating on plasma membranes have been studied more than those on tonoplasts. Recently, however, several breakthroughs have shed light on (1) the distinct roles of VSTs in plant development and stress responses and (2) how seemingly unrelated classes of VSTs act together to modulate sugar influx into and efflux from the vacuoles. Here we evaluate these advances, analyse the evolution of VSTs and identify knowledge gaps and future directions for better understanding and manipulation of cytosolic-vacuolar sugar exchange to optimize plant performance.

Tonoplast sugar transporters coordinately regulate tomato fruit development and quality

Fruit yield and quality are antagonistically regulated traits in tomato. An excessive focus on increasing yield often leads to a decline in quality. Achieving a delicate balance between high yield and desirable fruit quality is a challenging aspect of tomato breeding. In this study, we discovered that disrupting the function of the tomato tonoplast sugar transporter 3a (TST3a) significantly enhances both fruit weight and flavor. Three TSTs have been identified in tomato, namely SlTST1, SlTST3a, and SlTST3b; they possess the same sugar transport specificity for fructose and glucose and redundantly control cell expansion during fruit development. Sugar accumulation in sltst mutants correlates significantly with fruit size and flavor. The enlarged fruits in sltst3a mutants result from sugar accumulation due to the increased abundance of SlTST1 at the tonoplast coupled with the highest sugar transport capacity of SlTST1 among the three SlTSTs. Further experiments established that SlTST3a prevents the localization of SlTST1 to the tonoplast by inhibiting its interaction with VH1-interacting kinase (SlVIK). Mutation of SlTST3a in cultivated tomato can enhance both tomato fruit size and sugar content. Our findings offer potential avenues for simultaneously improving fruit quality and yield, providing valuable insights into the mechanisms underlying sugar storage during fruit development.

Mining and identification of factors influencing multi-branch plasticity in ornamental kale

MAIN CONCLUSION

Transcriptome-revealed plant hormones and nutrients are key factors influencing branching in ornamental kale. Topping treatment and exogenous hormones application revealed that auxin and SLs inhibited lateral buds outgrowth, respectively. Plant architecture is a crucial horticultural characteristic in ornamental kale as the variety of branching patterns significantly enhances the esthetic appeal of garden plants. The factors influencing multi-branch plasticity in ornamental kale are yet to be elucidated. In this study, we mined the key branching genes by comparing the transcriptomes of a single-branched inbred line 'P29' and its natural multi-branched mutant, revealing a total of 3727 differentially expressed genes (DEGs) between them. A Kyoto Encyclopedia of Genes and Genome enrichment analysis identified 41 auxin-related DEGs, 5 strigolactones (SLs)-related DEGs, 12 cytokinin-related DEGs, 3 abscisic acid-related DEGs, and 1 gibberellin-related DEG. Nutrients, such as sugar, nitrogen, and phosphorus, might also influence branching. To investigate the effects of auxin and SLs on branch outgrowth, we conducted a topping treatment (removed rosette head) and externally applied the SL analog GR24 and corresponding SL biosynthesis inhibitor TIS108 to the single-branch inbred line 'P23'. GR24 effectively inhibited lateral bud outgrowth while TIS108 promoted lateral bud initiation. This work provides a novel perspective of the multi-branch plasticity in ornamental kale and also highlights potential key elements regulating plant morphology, which could be targeted to improve the architecture of valuable plant species.

Functional crosstalk of sucrose and G protein signaling in maize thermotolerance by modulating osmoregulation system

Sucrose (SUC) is a signaling molecule with multiple physiological functions. G protein is a kind of receptor that converts extracellular first messenger into intracellular second messenger. However, it is little known that SUC interplays with G protein signaling in maize thermotolerance. In this work, using maize seedlings as materials, the interplay between SUC and G protein signaling in maize thermotolerance was investigated. The results indicate that heat stress-decreased survival percentage and tissue viability of the seedlings was mitigated by SUC. Similarly, heat stress-increased malondialdehyde content and electrolyte leakage also was reduced by SUC. These findings show that SUC can potentially enhance thermotolerance in maize seedlings. Also, SUC-enhanced thermotolerance was abolished by suramin (G protein inhibitor) and N-ethylmaleimide (SUC transport inhibitor), but enhanced by 3-O-methyl-D-glucose (G protein activator), indicating the interplay of SUC and G protein signaling in maize thermotolerance. To investigate the possible mechanism behind SUC-G protein interaction in enhancing maize thermotolerance, osmoregulation in mesocotyls of seedlings were evaluated before and after heat stress. The results suggest that osmolytes (SUC, glucose, fructose, total soluble sugar, proline, and glycine betaine) contents in mesocotyls under non-heat and heat stress were increased by SUC in varying degrees. Likewise, the osmolyte-metabolizing enzymes (sucrose-phosphate synthase, sucrose synthase, pyrroline-5-carboxylate synthase, ornithine aminotransferase, betaine-aldehyde dehydrogenase, and trehalase) activities were enhanced by SUC. Analogously, ZmSPS1, ZmSUS6, ZmP5CS, ZmOAT, ZmBADH, and ZmTRE1 expression in mesocotyls was up-regulated by SUC to different extent. These findings illustrate that the functional crosstalk of sucrose and G protein signaling in maize thermotolerance by modulating osmoregulation system.

Transcriptome and Metabolome Analyses Offer New Insights into Bolting Time Regulation in Broccoli

The globular buds and stems are the main edible organs of broccoli. Bolting is an important agronomic trait, and the timing of its occurrence is particularly critical when breeding and domesticating broccoli. The molecular mechanism that regulates broccoli bolting time is not well-understood. In this study, the apical flower bud and leaf tissues of two broccoli varieties with different bolting intensities were selected for metabolome and transcriptome analyses. In the apical flower buds of early-bolting B2554 and late-bolting B2557, 1094 differentially expressed genes and 206 differentially accumulated metabolites were identified. In the leaves, 487 differentially expressed genes and 40 differentially accumulated metabolites were identified. In the floral pathway, the expression of FLC (FLOWERING LOCUS C) was significantly upregulated, and that of FT (FLOWERING LOCUS T) was significantly downregulated in the late-bolting plants, indicating their possible role in suppressing bolting. In addition, significant differences were identified in the sucrose synthesis and transport, hormone synthesis, and signal transduction processes in early-bolting B2554 and late-bolting B2557. Sucrose accumulation in the leaves and apical flower buds of the early-bolting plants was about 1.3 times higher than in the late-bolting plants. Indole-3-acetic acid (IAA) and abscisic acid (ABA) accumulation in the apical flower buds of the late-bolting plants was more than twice that in the early-bolting plants. Jasmonic acid (JA) accumulation in the apical flower buds of the late-bolting plants was more than ten times higher than in the early-bolting plants. Phenolic acids may affect the bolting time of broccoli. This study offers new insights into the regulation mechanism of broccoli bolting and provides some potential molecular targets to include in breeding methods that regulate bolting time.

Telomere-to-telomere Phragmites australis reference genome assembly with a B chromosome provides insights into its evolution and polysaccharide biosynthesis

Phragmites australis is a globally distributed grass species (Poaceae) recognized for its vast biomass and exceptional environmental adaptability, making it an ideal model for studying wetland ecosystems and plant stress resilience. However, genomic resources for this species have been limited. In this study, we assembled a chromosome-level reference genome of P. australis containing one B chromosome. An explosion of LTR-RTs, centered on the Copia family, occurred during the late Pleistocene, driving the expansion of P. australis genome size and subgenomic differentiation. Comparative genomic analysis showed that P. australis underwent two whole gene duplication events, was segregated from Cleistogenes songorica at 34.6 Mya, and that 41.26% of the gene families underwent expansion. Based on multi-tissue transcriptomic data, we identified structural genes in the biosynthetic pathway of pharmacologically active Phragmitis rhizoma polysaccharides with essential roles in rhizome development. This study deepens our understanding of Arundinoideae evolution, genome dynamics, and the genetic basis of key traits, providing essential data and a genetic foundation for wetland restoration, bioenergy development, and plant stress.

Effects of retaining different number of mother bamboo on the growth and NSCs allocation of new-born seedlings in Phyllostachys edulis at different age

BACKGROUND

Non-structural carbohydrates (NSCs) are key substances for metabolic processes in plants, providing energy for growth, development, and responses to environmental stress. Pruning mother bamboo in a clump can significantly affect the NSCs allocation of new shoots, thereby affecting their growth. Moso bamboo (Phyllostachys edulis) is an important economic bamboo species with a highest planting area in China. However, it remains unclear how many mother bamboo left maximize the influence in moso bamboo seedlings at different age.

RESULTS

This study investigated the effects of retaining different number of mother bamboo on the morphological characterization and NSCs allocation of new-born seedlings in moso bamboo at two-year-old and three-year-old, respectively. Retaining more mother bamboo significantly promoted the plant height and diameter of new shoots, particularly in the two-year-old clumps. The growth rate of new shoots increased with the number of mother bamboo in the two-year-old clumps, while it remained relatively stable in the three-year-old clumps. The allocation strategy of NSCs also showed significant differences when retaining different number of mother bamboo across growth stages. NSCs content continuously increased with the growth of new shoots during the rapid growth phase, which reached peak in all parts at the end of the rhizome elongation stage. In two-year-old bamboo seedlings, the NSCs content increased with the number of retained mother plants. Significant differences were found between different treatments, particularly between those with one and four mother bamboos left. It was similar in the three-year-old clumps. However, there were no significant differences in NSCs content among the treatments.

CONCLUSION

Reducing the number of mother bamboo appropriately can promote the growth of new shoots in moso bamboo. The two-year-old clumps were more dependent on the number of mother bamboo, while it was less pronounced for three-year-old clumps. In production practice, it is recommended that three mother bamboos are retained for two-year-old clumps and two to three mother bamboos for three-year-old clumps. This approach can expand the afforestation area while ensuring the survival rate of new seedlings in moso bamboo.

Senescence-Associated Sugar Transporter1 affects developmental master regulators and controls senescence in Arabidopsis

Sugar transport across membranes is critical for plant development and yield. However, an analysis of the role of intracellular sugar transporters in senescence is lacking. Here, we characterized the role of Senescence-Associated Sugar Transporter1 (SAST1) during senescence in Arabidopsis (Arabidopsis thaliana). SAST1 expression was induced in leaves during senescence and after the application of abscisic acid (ABA). SAST1 is a vacuolar protein that pumps glucose out of the cytosol. sast1 mutants exhibited a stay-green phenotype during developmental senescence, after the darkening of single leaves, and after ABA feeding. To explain the stay-green phenotype of sast1 mutants, we analyzed the activity of the glucose-induced master regulator TOR (target of rapamycin), which is responsible for maintaining a high anabolic state. TOR activity was higher in sast1 mutants during senescence compared to wild types, whereas the activity of its antagonist, SNF1-related protein kinase 1 (SnRK1), was reduced in sast1 mutants under senescent conditions. This deregulation of TOR and SnRK1 activities correlated with high cytosolic glucose levels under senescent conditions in sast1 mutants. Although sast1 mutants displayed a functional stay-green phenotype, their seed yield was reduced. These analyses place the activity of SAST1 in the last phase of a leaf's existence in the molecular program required to complete its life cycle.

Dynamic changes of endogenous phytohormones and carbohydrates during spontaneous morphogenesis of Centaurium erythraea Rafn

Common centaury (Centaurium eryhtraea Rafn) is a medicinal plant species with vigorous morphogenic potential in vitro. The process of spontaneous shoot regeneration in a solid root culture is characteristic for this plant species. In this context, the aim of this work was to investigate the dynamic changes of endogenous phytohormones and carbohydrates content in root explants at different time points (0, 2, 4, 7, 14, 21, 28, and 60 days) during spontaneous centaury morphogenesis in vitro. Detailed analysis of cytokinins (CKs) showed that trans-zeatin (tZ) was the major bioactive CK at all time points. The corresponding riboside, tZ9R, was also determined in the majority of the identified transport forms, at all time-points. Further analysis of endogenous auxin revealed a significant increase in endogenous indole-3-acetic acid (IAA) after 21 days, when a huge jump in the ratio of IAA/bioactive CKs was also observed. The maximum total soluble sugar content was measured after 14 days, while a significant decrease was determined after 21 days, when the first regenerated adventitious shoots appeared. This undoubtedly indicates an increased energy requirement prior to the actual regeneration of the shoots. The obtained results indicate that the period from day 14 to day 21 involves the most dramatic disturbances in endogenous bioactive CKs, IAA and carbohydrate balance, which are very important and valuable factors for the onset of shoot regeneration.

Photosynthetic Electron Flows and Networks of Metabolite Trafficking to Sustain Metabolism in Photosynthetic Systems

Photosynthetic eukaryotes have metabolic pathways that occur in distinct subcellular compartments. However, because metabolites synthesized in one compartment, including fixed carbon compounds and reductant generated by photosynthetic electron flows, may be integral to processes in other compartments, the cells must efficiently move metabolites among the different compartments. This review examines the various photosynthetic electron flows used to generate ATP and fixed carbon and the trafficking of metabolites in the green alga Chlamydomomas reinhardtii; information on other algae and plants is provided to add depth and nuance to the discussion. We emphasized the trafficking of metabolites across the envelope membranes of the two energy powerhouse organelles of the cell, the chloroplast and mitochondrion, the nature and roles of the major mobile metabolites that move among these compartments, and the specific or presumed transporters involved in that trafficking. These transporters include sugar-phosphate (sugar-P)/inorganic phosphate (Pi) transporters and dicarboxylate transporters, although, in many cases, we know little about the substrate specificities of these transporters, how their activities are regulated/coordinated, compensatory responses among transporters when specific transporters are compromised, associations between transporters and other cellular proteins, and the possibilities for forming specific 'megacomplexes' involving interactions between enzymes of central metabolism with specific transport proteins. Finally, we discuss metabolite trafficking associated with specific biological processes that occur under various environmental conditions to help to maintain the cell's fitness. These processes include C4 metabolism in plants and the carbon concentrating mechanism, photorespiration, and fermentation metabolism in algae.

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

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

Carbohydrate distribution via SWEET17 is critical for Arabidopsis inflorescence branching under drought

Sugars Will Eventually be Exported Transporters (SWEETs) are the most recently discovered family of plant sugar transporters. By acting as uniporters, SWEETs facilitate the diffusion of sugars across cell membranes and play an important role in various physiological processes such as abiotic stress adaptation. AtSWEET17, a vacuolar fructose facilitator, was shown to be involved in the modulation of the root system during drought. In addition, previous studies have shown that overexpression of an apple homolog leads to increased drought tolerance in tomato plants. Therefore, SWEET17 might be a molecular element involved in plant responses to drought. However, the role and function of SWEET17 in above-ground tissues of Arabidopsis under drought stress remain elusive. By combining gene expression analysis and stem architecture with the sugar profiles of different above-ground tissues, we uncovered a putative role for SWEET17 in carbohydrate supply and thus cauline branch elongation, especially during periods of carbon limitation, as occurs under drought stress. Thus, SWEET17 seems to be involved in maintaining efficient plant reproduction under drought stress conditions.

Widely-targeted metabolomics and transcriptomics identify metabolites associated with flowering regulation of Choy Sum

Choy Sum, a stalk vegetable highly valued in East and Southeast Asia, is characterized by its rich flavor and nutritional profile. Metabolite accumulation is a key factor in Choy Sum stalk development; however, no research has focused on metabolic changes during the development of Choy Sum, especially in shoot tip metabolites, and their effects on growth and flowering. Therefore, in the present study, we used a widely targeted metabolomic approach to analyze metabolites in Choy Sum stalks at the seedling (S1), bolting (S3), and flowering (S5) stages. In total, we identified 493 metabolites in 31 chemical categories across all three developmental stages. We found that the levels of most carbohydrates and amino acids increased during stalk development and peaked at S5. Moreover, the accumulation of amino acids and their metabolites was closely related to G6P, whereas the expression of flowering genes was closely related to the content of T6P, which may promote flowering by upregulating the expressions of BcSOC1, BcAP1, and BcSPL5. The results of this study contribute to our understanding of the relationship between the accumulation of stem tip substances during development and flowering and of the regulatory mechanisms of stalk development in Choy Sum and other related species.

Vacuolar Sugar Transporter TMT2 Plays Crucial Roles in Germination and Seedling Development in Arabidopsis

Vacuolar sugar transporters transport sugar across the tonoplast, are major players in maintaining sugar homeostasis, and therefore play vital roles in plant growth, development, and biomass yield. In this study, we analyzed the physiological roles of the tonoplast monosaccharide transporter 2 (TMT2) in Arabidopsis. In contrast to the wild type (WT) that produced uniform seedlings, the tmt2 mutant produced three types of offspring: un-germinated seeds (UnG), seedlings that cannot form true leaves (tmt2-S), and seedlings that develop normally (tmt2-L). Sucrose, glucose, and fructose can substantially, but not completely, rescue the abnormal phenotypes of the tmt2 mutant. Abnormal cotyledon development, arrested true leaf development, and abnormal development of shoot apical meristem (SAM) were observed in tmt2-S seedlings. Cotyledons from the WT and tmt2-L seedlings restored the growth of tmt2-S seedlings through micrografting. Moreover, exogenous sugar sustained normal growth of tmt2-S seedlings with cotyledon removed. Finally, we found that the TMT2 deficiency resulted in growth defects, most likely via changing auxin signaling, target of rapamycin (TOR) pathways, and cellular nutrients. This study unveiled the essential functions of TMT2 for seed germination and initial seedling development, ensuring cotyledon function and mobilizing sugars from cotyledons to seedlings. It also expanded the current knowledge on sugar metabolism and signaling. These findings have fundamental implications for enhancing plant biomass production or seed yield in future agriculture.