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Main conclusion: Overexpression of OsSTP1 enhances the non-structural carbohydrate remobilization in the source, starch accumulation in grains, and the transportation of carbohydrates from source to sink during the filling stage. The sugar transporter protein (STP) is the best-characterized subfamily of the monosaccharide transporter (MST) family and plays critical roles in regulating plant stress tolerance, growth, and development. However, the role of STPs in regulating rice yield is poorly understood. In this study, we report that compared with Taipei 309, overexpression of OsSTP1 can achieve higher rice yield. We demonstrate that OsSTP1 mRNA levels are higher than those of the other seven STPs in mixed samples of leaf sheaths, stems, and nodes at 12 days after pollination (DAP). OsSTP1 is prominently expressed in the leaf sheaths, stems, and nodes at the grain filling stage. Subcellular localization analysis revealed that OsSTP1 is localized in the plasma membrane. Overexpression of OsSTP1 increased the activities of amylase (AMY) and sucrose phosphate synthase (SPS) in mixed samples of leaf sheaths, stems, and nodes at 12 DAP, the sucrose content of the phloem exudate, and accumulation of soluble sugars and starch in panicles, ultimately increasing seed-setting rates and grain yields in the Taipei 309 cultivar. These findings indicate that overexpression of OsSTP1 can improve grain yield by synergistically promoting non-structural carbohydrate (NSC) remobilization and transportation. [ABSTRACT FROM AUTHOR]

Summary: The mutualistic interaction between ectomycorrhizal fungi and trees is characterized by the coordinated exchange of soil nutrients with soluble sugars. Despite the importance of this process, the precise mechanism by which sugars are transported from host roots to colonizing hyphae remains unclear.This study aimed to identify the specific membrane transporters responsible for the unloading of sugars at the symbiotic interface, with a focus on the role of the root Sugars Will Eventually Be Exported Transporter (SWEET) uniporters.Our study used RNA sequencing and quantitative PCR to identify PtaSWEET gene expression in Populus tremula × alba–Laccaria bicolor ectomycorrhizal root tips. Our results suggest that symbiosis‐induced PtaSWEET1c is primarily responsible for transporting glucose and sucrose, as demonstrated by the yeast assays. Moreover, we used a promoter‐YFP reporter to confirm the localization of the PtaSWEET1c expression in cortical cells of ectomycorrhizal rootlets, supporting its major role in supplying glucose at the symbiotic interface. Furthermore, our observations confirmed the localization of PtaSWEET1c‐GFP in the plasma membrane. The inactivation of PtaSWEET1c reduced ectomycorrhizal root formation and 13C translocation to ectomycorrhizal roots.Our findings highlight the crucial role of PtaSWEET1c in facilitating glucose and sucrose transport at the symbiotic interface of Populus–L. bicolor symbiosis. [ABSTRACT FROM AUTHOR]

Background: Tea is an important cash crop that significantly contributes to rural development, poverty reduction and food security in many developing countries. It provides livelihoods for millions of smallholder producers and aids their economic stability. Anthocyanins in tea leaves provides excellent commercial quality and germplasm exploration potential. These compounds give tea leaves vibrant colors and increase health benefits. The current understanding of the synergistic regulation mechanisms responsible for color changes in purple tea, attributed to anthocyanin degradation, remains unclear. Results: In this study, we have identified 30 gene families within the genome that are associated to with anthocyanin metabolism from tea. These gene families play distinct roles in the biosynthesis of anthocyanin including the formation of the core, structure, modification of the molecular framework, facilitation of transport process, regulation of gene expression, breakdown pathways, sugar transportation and iron ion respectively. Subsequently, we investigated the synergistic mechanisms of anthocyanin metabolism related gene families within tea leaves using structural equation modeling. The results showed that sugar transport positively affects anthocyanin transportation, and promotes anthocyanin degradation during leaf pigmentation, whereas, it inhibits anthocyanin degradation during the fading of leaf color. Further, Iron ions facilitate the degradation of anthocyanins during their deposition and conversely, impede this degradation process during digestion. These finding suggests that tea plants may regulate the synthesis and degradation of anthocyanins through sugar transport and iron ions ensure healthy levels and vibrant colors. Conclusions: Our study contributes valuable information into the dynamic equilibrium anthocyanin mechanism and sheds light on complex regulatory mechanisms that govern the synthesis, transport and degradation of these pigments. These insights could be further used to develop strategies for enhancing anthocyanins content in unique tea germplasm to aid tea industry in producing new tea products with increased health benefits and aesthetic appeals. [ABSTRACT FROM AUTHOR]

Summary How carbon (sucrose) and nitrogen (amino acid) accumulation is coordinatively controlled in cereal grains remains largely enigmatic. We found that overexpression of the strigolactone (SL) biosynthesis gene CAROTENOID CLEAVAGE DIOXYGENASE 8 (CCD8) resulted in greater ear diameter and enhanced sucrose and amino acid accumulation in maize kernels. Loss of ZmCCD8 function reduced kernel growth with lower sugar and amino acid concentrations. Transcriptomic analysis showed down‐regulation of the transcription factors ZmMYB42 and ZmMYB63 in ZmCCD8 overexpression alleles and up‐regulation in zmccd8 null alleles. Importantly, ZmMYB42 and ZmMYB63 were negatively regulated by the SL signalling component UNBRANCHED 3, and repressed expression of the sucrose transporters ZmSWEET10 and ZmSWEET13c and the lysine/histidine transporter ZmLHT14. Consequently, null alleles of ZmMYB42 or ZmMYB63 promoted accumulation of soluble sugars and free amino acids in maize kernels, whereas ZmLHT14 overexpression enhanced amino acid accumulation in kernels. Moreover, overexpression of the SL receptor DWARF 14B resulted in more sucrose and amino acid accumulation in kernels, down‐regulation of ZmMYB42 and ZmMYB63 expression, and up‐regulation of ZmSWEETs and ZmLHT14 transcription. Together, we uncover a distinct SL signalling pathway that regulates sucrose and amino acid accumulation in kernels. Significant association of two SNPs in the 5′ upstream region of ZmCCD8 with ear and cob diameter implicates its potential in breeding toward higher yield and nitrogen efficiency. [ABSTRACT FROM AUTHOR]

Functional innovation at the protein level is a key source of evolutionary novelties. The constraints on functional innovations are likely to be highly specific in different proteins, which are shaped by their unique histories and the extent of global epistasis that arises from their structures and biochemistries. These contextual nuances in the sequence–function relationship have implications both for a basic understanding of the evolutionary process and for engineering proteins with desirable properties. Here, we have investigated the molecular basis of novel function in a model member of an ancient, conserved, and biotechnologically relevant protein family. These Major Facilitator Superfamily sugar porters are a functionally diverse group of proteins that are thought to be highly plastic and evolvable. By dissecting a recent evolutionary innovation in an α-glucoside transporter from the yeast Saccharomyces eubayanus , we show that the ability to transport a novel substrate requires high-order interactions between many protein regions and numerous specific residues proximal to the transport channel. To reconcile the functional diversity of this family with the constrained evolution of this model protein, we generated new, state-of-the-art genome annotations for 332 Saccharomycotina yeast species spanning ∼400 My of evolution. By integrating phylogenetic and phenotypic analyses across these species, we show that the model yeast α-glucoside transporters likely evolved from a multifunctional ancestor and became subfunctionalized. The accumulation of additive and epistatic substitutions likely entrenched this subfunction, which made the simultaneous acquisition of multiple interacting substitutions the only reasonably accessible path to novelty. [ABSTRACT FROM AUTHOR]

The import of plant-derived small sugars by sugar transporters (STs) has received increasing interest due to its important biological role and great industrial potential. STs are important targets of genetic engineering to improve fungal plant biomass conversion. Comparatively analysis of the genome-wide prevalence and transcriptomics of STs was performed in four filamentous fungi: Aspergillus niger, Aspergillus nidulans, Penicillium subrubescens and Trichoderma reesei. Using phylogenetic analysis and literature mining, their predicted STs were divided into ten subfamilies with putative sugar specificities assigned. In addition, transcriptome analysis revealed complex expression profiles among different STs subfamilies and fungal species, indicating a sophisticated transcriptome regulation and functional diversity of fungal STs. Several STs showed strong co-expression with other genes involved in sugar utilization, encoding CAZymes and sugar catabolic enzymes. This study provides new insights into the diversity of STs at the genomic/transcriptomic level, facilitating their biochemical characterization and metabolic engineering.

Heterotrophic microbes rely on host‐derived carbon sources for their growth and survival. Depriving pathogens of plant carbon is therefore a promising strategy for protecting plants from disease and reducing yield losses. Importantly, this carbon starvation‐mediated resistance is expected to be more broad‐spectrum and durable than race‐specific R‐gene‐mediated resistance. Although sugars are well characterized as major carbon sources for bacteria, emerging evidence suggests that plant‐derived lipids are likely to be an essential carbon source for some fungal microbes, particularly biotrophs. Here, we comprehensively discuss the dual roles of carbon sources (mainly sugars and lipids) and their transport processes in immune signalling and microbial nutrition. We summarize recent findings revealing the crucial roles of lipids as susceptibility factors at all stages of pathogen infection. In particular, we discuss the potential pathways by which lipids and other plant carbon sources are delivered to biotrophs, including protein‐mediated transport, vesicle trafficking and autophagy. Finally, we highlight knowledge gaps and offer suggestions for clarifying the mechanisms that underlie nutrient uptake by biotrophs, providing guidance for future research on the application of carbon starvation–mediated resistance. Summary statement: This review summarizes the roles of host carbon sources in plant–microbe interactions, highlights the carbon nutrition and susceptibility factor roles of host lipids for biotrophic fungi and outlines several host transport processes that potentially contribute to fungal carbon acquisition. [ABSTRACT FROM AUTHOR]

Summary: In photosynthetic cells, plants convert carbon dioxide to sugars that can be moved between cellular compartments by transporters before being subsequently metabolized to support plant growth and development. Most pathogens cannot synthesize sugars directly but have evolved mechanisms to obtain plant‐derived sugars as C resource for successful infection and colonization. The availability of sugars to pathogens can determine resistance or susceptibility. Here, we summarize current progress on the roles of sugar transporters in plant–pathogen interactions. We highlight how transporters are manipulated antagonistically by both host and pathogens in competing for sugars. We examine the potential application of this target in resistance breeding and discuss opportunities and challenges for the future. [ABSTRACT FROM AUTHOR]

Coconut (Cocos nucifera L.) is an important agricultural commodity with substantial economic and nutritional value, widely used for various products, including coconut water. The sweetness is an important quality trait of coconut water, which is influenced by genetic and environmental factors. In this study, we utilized next-generation sequencing to identify genetic variations in the coconut genome associated with the sweetness of coconut water. Whole-genome resequencing of 49 coconut accessions, including diverse germplasm and an F2 population of 81 individuals, revealed ~27 M SNPs and ~1.5 M InDels. Sugar content measured by °Bx was highly variable across all accessions tested, with dwarf varieties generally sweeter. A comprehensive analysis of the sugar profiles revealed that sucrose was the major sugar contributing to sweetness. Allele mining of the 148 genes involved in sugar metabolism and transport and genotype–phenotype association tests revealed two significant SNPs in the hexose carrier protein (Cnu01G018720) and sucrose synthase (Cnu09G011120) genes associated with the higher sugar content in both the germplasm and F2 populations. This research provides valuable insights into the genetic basis of coconut sweetness and offers molecular markers for breeding programs aimed at improving coconut water quality. The identified variants can improve the selection process in breeding high-quality sweet coconut varieties and thus support the economic sustainability of coconut cultivation. [ABSTRACT FROM AUTHOR]

This research cloned and expressed the sugar transporter gene KM_SUT5 from Kluyveromyces marxianus GX-UN120, which displayed remarkable sugar transportation capabilities, including pentose sugars. To investigate the impact of point mutations on xylose transport capacity, we selected four sites, predicted the suitable amino acid sites by molecular docking, and altered their codons to construct the corresponding mutants, Q74D, Y195K, S460H, and Q464F, respectively. Furthermore, we conducted site-directed truncation on six sites of KM_SUT5p. The molecular modification resulted in significant changes in mutant growth and the D-xylose transport rate. Specifically, the S460H mutant exhibited a higher growth rate and demonstrated excellent performance across 20 g L−1 xylose, achieving the highest xylose accumulation under xylose conditions (49.94 μmol h−1 gDCW-1, DCW mean dry cell weight). Notably, mutant delA554-, in which the transporter protein SUT5 is truncated at position delA554-, significantly increased growth rates in both D-xylose and D-glucose substrates. These findings offer valuable insights into potential modifications of other sugar transporters and contribute to a deeper understanding of the C-terminal function of sugar transporters. [ABSTRACT FROM AUTHOR]

Sugar, the primary product of photosynthesis, is a vital requirement for cell activities. Allocation of sugar from source to sink tissues is facilitated by sugar transporters (ST). These STs belong to the Major Facilitator Superfamily (MFS), the largest family of STs in plants. In this study, we performed genome wide and gene expression data analysis to identify the putative ST genes in Erianthus rufipilus (E. rufipilus) and in Saccharum officinarum (S. officinarum). We identified 78 ST gene families in E. rufipilus and 86 ST gene families in S. officinarum. Phylogenetic analysis distributed the ST genes into eight distinct subfamilies (INT, MST, VGT, pGlcT, PLT, STP, SFP and SUT). Chromosomal distribution of ST genes clustered them on 10 respective chromosomes. Furthermore, synteny analysis with S. spontaneum and Sorghum bicolor (S. bicolor) revealed highly colinear regions. Synonymous and non-synonymous ratio (Ka/Ks) showed purifying selection in gene evolution. Promoter analysis identified several cis-regulatory elements, mainly associated with light responsiveness. We also examined the expression pattern of ST genes in different developing tissues (mature leaf, pre-mature stem, mature stem and seedling stem). Under sugar stress, we identified the significant ST genes showing differential expression patterns. Moreover, our yeast one-hybrid (Y1H) assays identified NAM, ATAF and CUC (NAC) and Lesion Simulating Disease (LSD) potential transcription factors (TFs) that may bind to the SUT1-T1 promoter in S. officinarum, showing negative correlation pattern with SUT1-T1. Our results deepen our understanding of ST gene evolution in Saccharum species and will facilitate the future investigation of functional analysis of the ST gene family.

The SWEET sugar transporter plays a fundamental role in plant growth and development. In this study, 18 SWEET genes were identified from sweet sorghum (Sorghum dochna), encoding proteins with 231–336 amino acids, molecular weights from 25.15 to 35.69 kDa, and isoelectric points ranging between 6.41 and 9.69. Phylogenetic analysis categorized these proteins into four distinct subgroups. Examination of spatial expression patterns demonstrated that SdSWEET genes were expressed in a tissue-specific manner. Furthermore, their involvement in responses to various abiotic stresses, including cold, heat, drought, and salinity was observed. A yeast complementation assay verified that SdSWEET01, located on the plasma membrane, selectively transported glucose, sucrose, and galactose, while excluding fructose. Transgenic Arabidopsis expressing SdSWEET01 exhibited enhanced sugar absorption compared to wild-type plants, resulting in increased sensitivity and growth inhibition under high-sugar conditions. The study provides a detailed functional characterization of SdSWEET genes and emphasizes the critical role of SdSWEET01 in regulating sugar transport.

Abstract Most of the carbon found in fruits at harvest is imported by the phloem. Imported carbon provide the material needed for the accumulation of sugars, organic acids, secondary compounds, in addition to the material needed for the synthesis of cell walls. The accumulation of sugars during fruit development influences not only sweetness but also various parameters controlling fruit composition (fruit “quality”). The accumulation of organic acids and sugar in grape berry flesh cells is a key process for berry development and ripening. The present review presents an update of the research on grape berry development, anatomical structure, sugar and acid metabolism, sugar transporters, and regulatory factors.

The SWEET (sugar will eventually be exported transporter) family proteins are a recently identified class of sugar transporters that are essential for various physiological processes. Although the functions of the SWEET proteins have been identified in a number of species, to date, there have been no reports of the functions of the SWEET genes in woodland strawberries (Fragaria vesca). In this study, we identified 15 genes that were highly homologous to the A. thaliana AtSWEET genes and designated them as FvSWEET1 – FvSWEET15. We then conducted a structural and evolutionary analysis of these 15 FvSWEET genes. The phylogenetic analysis enabled us to categorize the predicted 15 SWEET proteins into four distinct groups. We observed slight variations in the exon‒intron structures of these genes, while the motifs and domain structures remained highly conserved. Additionally, the developmental and biological stress expression profiles of the 15 FvSWEET genes were extracted and analyzed. Finally, WGCNA coexpression network analysis was run to search for possible interacting genes of FvSWEET genes. The results showed that the FvSWEET10 genes interacted with 20 other genes, playing roles in response to bacterial and fungal infections. The outcomes of this study provide insights into the further study of FvSWEET genes and may also aid in the functional characterization of the FvSWEET genes in woodland strawberries. [ABSTRACT FROM AUTHOR]

Pepper (Capsicum annuum L.) is one of the most important economic crops in the world. By controlling the transport and distribution of photosynthetic products between cells and organs, sugar transporters are widely involved in growth and development, environmental adaptation, and microbial interactions. The present study was carried out at the genome-wide level to systematically characterize sugar transporters. As a result, 50 MST, 3 SUT, and 29 SWEET genes were identified and classified. The expression pattern of sugar transporters in pepper was analyzed by transcriptomic data. The expression properties of sugar transporters were further explored in pepper varieties with significant differences in weight, shape, and pungency. It was shown that the pepper sugar transporter genes had obvious spatiotemporal specific expression characteristics and exhibited variety-specific expression preferences. We focus on analyzing candidate genes that may be involved in fruit development and expansion. We further explore the response of pepper sugar transporters to adversity stress using a structural equation model. Finally, we found that the MST, SUT, and SWEET families are collectively involved in balancing pepper resistance to abiotic stress by coordinating the expression strengths of different family members. Our study may contribute to the functional study of pepper sugar transporter genes and create the prospect of utilizing sugar transporter gene resources to improve pepper variety. [ABSTRACT FROM AUTHOR]

Most of the carbon found in fruits at harvest is imported by the phloem. Imported carbon provide the material needed for the accumulation of sugars, organic acids, secondary compounds, in addition to the material needed for the synthesis of cell walls. The accumulation of sugars during fruit development influences not only sweetness but also various parameters controlling fruit composition (fruit "quality"). The accumulation of organic acids and sugar in grape berry flesh cells is a key process for berry development and ripening. The present review presents an update of the research on grape berry development, anatomical structure, sugar and acid metabolism, sugar transporters, and regulatory factors. [ABSTRACT FROM AUTHOR]

Beneficial Bacillus subtilis (BS) symbiosis could combat root pathogenesis, but it relies on root‐secreted sugars. Understanding the molecular control of sugar flux during colonization would benefit biocontrol applications. The SWEET (Sugar Will Eventually Be Exported Transporter) uniporter regulates microbe‐induced sugar secretion from roots; thus, its homologs may modulate sugar distribution upon BS colonization. Quantitative polymerase chain reaction revealed that gene transcripts of SWEET2, but not SWEET16 and 17, were significantly induced in seedling roots after 12 h of BS inoculation. Particularly, SWEET2‐β‐glucuronidase fusion proteins accumulated in the apical mature zone where BS abundantly colonized. Yet, enhanced BS colonization in sweet2 mutant roots suggested a specific role for SWEET2 to constrain BS propagation, probably by limiting hexose secretion. By employing yeast one‐hybrid screening and ectopic expression in Arabidopsis protoplasts, the transcription factor AHL29 was identified to function as a repressor of SWEET2 expression through the AT‐hook motif. Repression occurred despite immunity signals. Additionally, enhanced SWEET2 expression and reduced colonies were specifically detected in roots of BS‐colonized ahl29 mutant. Taken together, we propose that BS colonization may activate repression of AHL29 on SWEET2 transcription that would be enhanced by immunity signals, thereby maintaining adequate sugar secretion for a beneficial Bacillus association. Summary statement: Arabidopsis vacuolar SWEET2 transporter limits root sugar secretion upon colonization with beneficial Bacillus subtilis. The AT‐hook protein AHL29 binds to the SWEET2 promoter to repress its immunity‐induced expression, thereby promoting adequate carbon for a mutualistic association with Bacillus. [ABSTRACT FROM AUTHOR]

Sugar transporters play important roles in plant growth and development, flowering and fruiting, as well as responses to adverse abiotic and biotic environmental conditions. Lilies (Lilium spp.) are some of the most representative ornamental bulbous flowers. Sugar metabolism is critical for bulb formation in lilies; therefore, clarifying the amount and expression pattern of sugar transporters is essential for further analyzing their roles in bulb formation. In this study, based on the transcriptome data of the Lilium Oriental hybrid 'Sorbonne' and Lilium × formolongi, a total of 69 and 41 sugar transporters were identified in 'Sorbonne' and Lilium × formolongi, respectively, by performing bioinformatics analysis. Through phylogenetic analysis, monosaccharide transporters (MSTs) can be divided into seven subfamilies, sucrose transporters (SUTs) can be divided into three subgroups, and sugars will eventually be exported transporters (SWEETs) can be divided into four clades. According to an analysis of conserved motifs, 20, 14, and 12 conserved motifs were predicted in MSTs, SUTs, and SWEETs, respectively. A conserved domain analysis showed that MSTs and SUTs contained a single domain, whereas most of the SWEETs harbored two MtN3/saliva domains, also known as a PQ-loop repeat. The LohINT1, which was predicted to have a smaller number of transmembrane structural domains, was cloned and analyzed for subcellular localization. It was found that the LohINT1 protein is mainly localized in the cell membrane. In addition, the expression analysis indicated that 22 LohMSTs, 1 LohSUTs, and 5 LohSWEETs were upregulated in 'Sorbonne' 1 day after scale detachment treatment, suggesting that they may regulate the initiation of the bulblet. A total of 10 LflMSTs, 1 LflSUTs, and 6 LflSWEETs were upregulated 4~6 months after sowing, which corresponds to the juvenile-to-adult transition phase of Lilium × formolongi, suggesting that they may also play a role in the accompanying bulb swelling process. Combined with quantitative real-time PCR (qRT-PCR) analysis, LohSTP8 and LohSTP12 were significantly overexpressed during the extremely early stage of bulblet initiation, and LflERD6.3 was significantly overexpressed during the growth of the underground bulblet, suggesting that they may be key sugar transporters in the formation of lily bulbs, which needs further functional verification. [ABSTRACT FROM AUTHOR]

Sugar is an indispensable source of energy for plant growth and development, and it requires the participation of sugar transporter proteins (STPs) for crossing the hydrophobic barrier in plants. Here, we systematically identified the genes encoding sugar transporters in the genome of maize (Zea mays L.), analyzed their expression patterns under different conditions, and determined their functions in disease resistance. The results showed that the mazie sugar transporter family contained 24 members, all of which were predicted to be distributed on the cell membrane and had a highly conserved transmembrane transport domain. The tissue-specific expression of the maize sugar transporter genes was analyzed, and the expression level of these genes was found to be significantly different in different tissues. The analysis of biotic and abiotic stress data showed that the expression levels of the sugar transporter genes changed significantly under different stress factors. The expression levels of ZmSTP2 and ZmSTP20 continued to increase following Fusarium graminearum infection. By performing disease resistance analysis of zmstp2 and zmstp20 mutants, we found that after inoculation with Cochliobolus carbonum, Setosphaeria turcica, Cochliobolus heterostrophus, and F. graminearum, the lesion area of the mutants was significantly higher than that of the wild-type B73 plant. In this study, the genes encoding sugar transporters in maize were systematically identified and analyzed at the whole genome level. The expression patterns of the sugar transporter-encoding genes in different tissues of maize and under biotic and abiotic stresses were revealed, which laid an important theoretical foundation for further elucidation of their functions.

Coconut (Cocos nucifera L.) is an important agricultural commodity with substantial economic and nutritional value, widely used for various products, including coconut water. The sweetness is an important quality trait of coconut water, which is influenced by genetic and environmental factors. In this study, we utilized next-generation sequencing to identify genetic variations in the coconut genome associated with the sweetness of coconut water. Whole-genome resequencing of 49 coconut accessions, including diverse germplasm and an F2 population of 81 individuals, revealed ~27 M SNPs and ~1.5 M InDels. Sugar content measured by °Bx was highly variable across all accessions tested, with dwarf varieties generally sweeter. A comprehensive analysis of the sugar profiles revealed that sucrose was the major sugar contributing to sweetness. Allele mining of the 148 genes involved in sugar metabolism and transport and genotype–phenotype association tests revealed two significant SNPs in the hexose carrier protein (Cnu01G018720) and sucrose synthase (Cnu09G011120) genes associated with the higher sugar content in both the germplasm and F2 populations. This research provides valuable insights into the genetic basis of coconut sweetness and offers molecular markers for breeding programs aimed at improving coconut water quality. The identified variants can improve the selection process in breeding high-quality sweet coconut varieties and thus support the economic sustainability of coconut cultivation.

Abstract Background Filamentous fungi possess a rich CAZymes system, which is widely studied and applied in the bio-conversion of plant biomass to alcohol chemicals. Carbon source acquisition is the fundamental driver for CAZymes-producing sustainability and secondary metabolism, therefore, a deeper insight into the regulatory network of sugar transport in filamentous fungi has become urgent. Results This study reports an important linkage of sulfur assimilation to lignocellulose response of filamentous fungus. Inorganic sulfur addition facilitated biodegradation of rice straw by Trichoderma guizhouense NJAU4742. Cysteine and glutathione were revealed as major intracellular metabolites responsive to sulfur addition by metabolomics, cysteine content was increased in this process and glutathione increased correspondingly. Two membrane sugar transporter genes, Tgmst1 and Tgmst2, were identified as the critical response genes significantly up-regulated when intracellular cysteine increased. Tgmst1 and Tgmst2 were both positively regulated by the glucose regulation-related protein (GRP), up-regulation of both Tgmst1 and Tggrp can cause a significant increase in intracellular glucose. The transcriptional regulatory function of GRP mainly relied on GSH-induced glutathionylation, and the transcription activating efficiency was positively related to the glutathionylation level, furthermore, DTT-induced deglutathionylation resulted in the down-regulation of downstream genes. Conclusions Inorganic sulfur addition induces a rise in intracellular Cys content, and the conversion of cysteine to glutathione caused the increase of glutathionylation level of GRP, which in turn up-regulated Tgmst1 and Tgmst2. Subsequently, the sugar transport efficiency of single cells was improved, which facilitated the maintenance of vigorous CAZymes metabolism and the straw-to-biomass conversion.

False smut, caused by Villosiclava virens, is becoming increasingly serious in modern rice production systems, leading to yield losses and quality declines. Successful infection requires efficient acquisition of sucrose, abundant in rice panicles, as well as other sugars. Sugar transporters (STPs) may play an important role in this process. STPs belong to a major facilitator superfamily, which consists of large multigenic families necessary to partition sugars between fungal pathogens and their hosts. This study identified and characterized the STP family of V. viren, and further analyzed their gene functions to uncover their roles in interactions with rice. Through genome-wide and systematic bioinformatics analyses, 35 STPs were identified from V.virens and named from VvSTP1 to VvSTP35. Transmembrane domains, gene structures, and conserved motifs of VvSTPs have been identified and characterized through the bioinformatic analysis. In addition, a phylogenetic analysis revealed relationship between VvSTPs and STPs from the other three reference fungi. According to a qRT-PCR and RNA-sequencing analysis, VvSTP expression responded differently to different sole carbon sources and H2O2 treatments, and changed during the pathogenic process, suggesting that these proteins are involved in interactions with rice and potentially functional in pathogenesis. In total, 12 representative VvSTPs were knocked out through genetic recombination in order to analyze their roles in pathogenicity of V. virens. The knock-out mutants of VvSTPs showed little difference in mycelia growth and conidiation, indicating a single gene in this family cannot influence vegetative growth of V. virens. It is clear, however, that these mutants result in a change in infection efficiency in a different way, indicating that VvSTPs play an important role in the pathogenicity of virens. This study is expected to contribute to a better understanding of how host-derived sugars contribute to V. virens pathogenicity. [ABSTRACT FROM AUTHOR]

Introduction: Streptococcus thermophilus is a traditional starter for dairy products. The lactose rich in milk is the main carbon source for the growth of S. thermophilus. However, the utilization of galactose by S. thermophilus is strain-specific, and many genetic factors can affect the sugar utilization phenotype of S. thermophilus strains. Methods: In this study, S. thermophilus A25, which is capable of utilizing lactose and galactose, was used as the starting strain to construct lactose permease-deficient mutant S. thermophilus ΔlacS. Subsequently, the complement vectors expressing complete lactose permease of S. thermophilus and its N-terminal 1–486 amino acid residues were constructed and transformed into S. thermophilus ΔlacS, respectively. Meanwhile, complement vectors expressing lactose permease and galactose/proton symporter of Escherichia coli were also constructed. Results and Discussion: Results showed that S. thermophilus ΔlacS lost the ability to utilize lactose and galactose. By measuring the growth of the recombinant strains, it was found that the strain expressing complete lactose permease of S. thermophilus recovered the growth ability in lactose and galactose medium, while the strain expressing N-terminal of lactose permease recovered the growth ability only in lactose medium. Furthermore, the transformation of S. thermophilus ΔlacS was not successful with the complement vector expressing E. coli lactose permease, while the strain expressing E. coli galactose/proton symporter could recover its growth ability in the galactose medium. These results suggest that the properties of sugar transporters play an important role in galactose utilization by S. thermophilus. [ABSTRACT FROM AUTHOR]

Abstract Background Dendrobium officinale Kimura et Migo (D. officinale) is a well-known traditional Chinese medicine with high content polysaccharides in stems. The SWEET (Sugars Will Eventually be Exported Transporters) family is a novel class of sugar transporters mediating sugar translocation among adjacent cells of plants. The expression patterns of SWEETs and whether they are associated with stress response in D. officinale remains uncovered. Results Here, 25 SWEET genes were screened out from D. officinale genome, most of which typically contained seven transmembrane domains (TMs) and harbored two conserved MtN3/saliva domains. Using multi-omics data and bioinformatic approaches, the evolutionary relationship, conserved motifs, chromosomal location, expression patterns, correlationship and interaction network were further analyzed. DoSWEETs were intensively located in nine chromosomes. Phylogenetic analysis revealed that DoSWEETs were divided into four clades, and conserved motif 3 specifically existed in DoSWEETs from clade II. Different tissue-specific expression patterns of DoSWEETs suggested the division of their roles in sugar transport. In particular, DoSWEET5b, 5c, and 7d displayed relatively high expression levels in stems. DoSWEET2b and 16 were significantly regulated under cold, drought, and MeJA treatment, which were further verified using RT-qPCR. Correlation analysis and interaction network prediction discovered the internal relationship of DoSWEET family. Conclusions Taken together, the identification and analysis of the 25 DoSWEETs in this study provide basic information for further functional verification in D. officinale.

Abstract Background Induction of cellulase in cellulolytic fungi Trichoderma reesei is strongly activated by cellulosic carbon sources. The transport of cellulosic inducer and the perception of inducing signal is generally considered as the critical process for cellulase induction, that the inducing signal would be perceived by a sugar transporter/transceptor in T. reesei. Several sugar transporters are coexpressed during the induction stage, but which function they serve and how they work collaboratively are still difficult to elucidate. Results In this study, we found that the constitutive expression of the cellulose response transporter-like protein CRT2 (previously identified as putative lactose permease TRE77517) improves cellulase induction on a cellulose, cellobiose or lactose medium. Functional studies indicate that the membrane-bound CRT2 is not a transporter of cellobiose, lactose or glucose in a yeast system, and it also does not affect cellobiose and lactose utilization in T. reesei. Further study reveals that CRT2 has a slightly similar function to the cellobiose transporter CRT1 in cellulase induction. Overexpression of CRT2 led to upregulation of CRT1 and the key transcription factor XYR1. Moreover, overexpression of CRT2 could partially compensate for the function loss of CRT1 on cellulase induction. Conclusions Our study uncovers the novel function of CRT2 in cellulase induction collaborated with CRT1 and XYR1, possibly as a signal transductor. These results deepen the understanding of the influence of sugar transporters in cellulase production.

Pepper (Capsicum annuum L.) is one of the most important economic crops in the world. By controlling the transport and distribution of photosynthetic products between cells and organs, sugar transporters are widely involved in growth and development, environmental adaptation, and microbial interactions. The present study was carried out at the genome-wide level to systematically characterize sugar transporters. As a result, 50 MST, 3 SUT, and 29 SWEET genes were identified and classified. The expression pattern of sugar transporters in pepper was analyzed by transcriptomic data. The expression properties of sugar transporters were further explored in pepper varieties with significant differences in weight, shape, and pungency. It was shown that the pepper sugar transporter genes had obvious spatiotemporal specific expression characteristics and exhibited variety-specific expression preferences. We focus on analyzing candidate genes that may be involved in fruit development and expansion. We further explore the response of pepper sugar transporters to adversity stress using a structural equation model. Finally, we found that the MST, SUT, and SWEET families are collectively involved in balancing pepper resistance to abiotic stress by coordinating the expression strengths of different family members. Our study may contribute to the functional study of pepper sugar transporter genes and create the prospect of utilizing sugar transporter gene resources to improve pepper variety.

Sweet sorghum has emerged as a promising source of bioenergy mainly due to its high biomass and high soluble sugar yield in stems. Studies have shown that loss-offunction Dry locus alleles have been selected during sweet sorghum domestication, and decapitation can further boost sugar accumulation in sweet sorghum, indicating that the potential for improving sugar yields is yet to be fully realized. To maximize sugar accumulation, it is essential to gain a better understanding of the mechanism underlying the massive accumulation of soluble sugars in sweet sorghum stems in addition to the Dry locus. We performed a transcriptomic analysis upon decapitation of near-isogenic lines for mutant (d, juicy stems, and green leaf midrib) and functional (D, dry stems and white leaf midrib) alleles at the Dry locus. Our analysis revealed that decapitation suppressed photosynthesis in leaves, but accelerated starch metabolic processes in stems. SbbHLH093 negatively correlates with sugar levels supported by genotypes (DD vs. dd), treatments (control vs. decapitation), and developmental stages post anthesis (3d vs.10d). D locus gene SbNAC074A and other programmed cell death-related genes were downregulated by decapitation, while sugar transporter-encoding gene SbSWEET1A was induced. Both SbSWEET1A and Invertase 5 were detected in phloem companion cells by RNA in situ assay. Loss of the SbbHLH093 homolog, AtbHLH093, in Arabidopsis led to a sugar accumulation increase. This study provides new insights into sugar accumulation enhancement in bioenergy crops, which can be potentially achieved by reducing reproductive sink strength and enhancing phloem unloading. [ABSTRACT FROM AUTHOR]

Selective abortion of grain siblings in a panicle or ear is conserved in cereals, and severely limits yield potential. The fate of grain siblings is established during or soon after fertilization, a narrow window of high sensitivity to stresses. Grain set is sink-limited, as leaf photosynthesis has reached the maximum and the amount of assimilates required (mainly as sucrose) for grain set is small. Understanding sugar import into, and metabolism within, the ovaries and grains is essential for designing approaches to alleviate abortion, thereby increasing yield, an urgent task facing humankind. An inherent asynchrony in pollination and fertilization among ovaries of a spike or ear determines the spatiotemporal hierarchy in sugar uptake potential and grain fate. Emerging findings support the idea of a complex regulation of sugar delivery across the grain maternal–filial interface, a critical step for grain set. As an evolutionary strategy, plants overproduce ovaries as a safety net for survival, with those losing in the competition for resources being aborted. Grain abortion is, however, highly detrimental agronomically. The molecular basis of selective abortion of grain siblings remains unknown. In this opinion article we assess the current understanding of the molecular players controlling carbon resource import into ovaries and young grains, followed by an evaluation of the spatial hierarchy of sink capacity among grain siblings, focusing on the roles exerted by sugar transporters and enzymes. We argue that, upon sequential pollination and fertilization, robust activation of the carbon import and sugar signaling system plays a key role in establishing the capacity of grain siblings to acquire enough carbon resources to survive and thrive. [ABSTRACT FROM AUTHOR]

Rice sheath blight (ShB) disease poses a major threat to rice yield throughout the world. However, the defense mechanisms against ShB in rice remain largely unknown. ShB resistance is a typical quantitative trait controlled by multiple genes. With the rapid development of molecular methods, many quantitative trait loci (QTLs) related to agronomic traits, biotic and abiotic stresses, and yield have been identified by genome-wide association studies. The interactions between plants and pathogens are controlled by various plant hormone signaling pathways, and the pathways synergistically or antagonistically interact with each other, regulating plant growth and development as well as the defense response. This review summarizes the regulatory effects of hormones including auxin, ethylene, salicylic acid, jasmonic acid, brassinosteroids, gibberellin, abscisic acid, strigolactone, and cytokinin on ShB and the crosstalk between the various hormones. Furthermore, the effects of sugar and nitrogen on rice ShB resistance, as well as information on genes related to ShB resistance in rice and their effects on ShB are also discussed. In summary, this review is a comprehensive description of the QTLs, hormones, nutrition, and other defense-related genes related to ShB in rice. The prospects of targeting the resistance mechanism as a strategy for controlling ShB in rice are also discussed. [ABSTRACT FROM AUTHOR]

Background: Induction of cellulase in cellulolytic fungi Trichoderma reesei is strongly activated by cellulosic carbon sources. The transport of cellulosic inducer and the perception of inducing signal is generally considered as the critical process for cellulase induction, that the inducing signal would be perceived by a sugar transporter/transceptor in T. reesei. Several sugar transporters are coexpressed during the induction stage, but which function they serve and how they work collaboratively are still difficult to elucidate. Results: In this study, we found that the constitutive expression of the cellulose response transporter-like protein CRT2 (previously identified as putative lactose permease TRE77517) improves cellulase induction on a cellulose, cellobiose or lactose medium. Functional studies indicate that the membrane-bound CRT2 is not a transporter of cellobiose, lactose or glucose in a yeast system, and it also does not affect cellobiose and lactose utilization in T. reesei. Further study reveals that CRT2 has a slightly similar function to the cellobiose transporter CRT1 in cellulase induction. Overexpression of CRT2 led to upregulation of CRT1 and the key transcription factor XYR1. Moreover, overexpression of CRT2 could partially compensate for the function loss of CRT1 on cellulase induction. Conclusions: Our study uncovers the novel function of CRT2 in cellulase induction collaborated with CRT1 and XYR1, possibly as a signal transductor. These results deepen the understanding of the influence of sugar transporters in cellulase production. [ABSTRACT FROM AUTHOR]

Background: Dendrobium officinale Kimura et Migo (D. officinale) is a well-known traditional Chinese medicine with high content polysaccharides in stems. The SWEET (Sugars Will Eventually be Exported Transporters) family is a novel class of sugar transporters mediating sugar translocation among adjacent cells of plants. The expression patterns of SWEETs and whether they are associated with stress response in D. officinale remains uncovered. Results: Here, 25 SWEET genes were screened out from D. officinale genome, most of which typically contained seven transmembrane domains (TMs) and harbored two conserved MtN3/saliva domains. Using multi-omics data and bioinformatic approaches, the evolutionary relationship, conserved motifs, chromosomal location, expression patterns, correlationship and interaction network were further analyzed. DoSWEETs were intensively located in nine chromosomes. Phylogenetic analysis revealed that DoSWEETs were divided into four clades, and conserved motif 3 specifically existed in DoSWEETs from clade II. Different tissue-specific expression patterns of DoSWEETs suggested the division of their roles in sugar transport. In particular, DoSWEET5b, 5c, and 7d displayed relatively high expression levels in stems. DoSWEET2b and 16 were significantly regulated under cold, drought, and MeJA treatment, which were further verified using RT-qPCR. Correlation analysis and interaction network prediction discovered the internal relationship of DoSWEET family. Conclusions: Taken together, the identification and analysis of the 25 DoSWEETs in this study provide basic information for further functional verification in D. officinale. [ABSTRACT FROM AUTHOR]

Sugars are the principal carbon and energy sources and serve as osmotic regulators and radical scavengers, thus playing an important role in plant responses to drought. Sugar transporters steering the distribution of sugar are vital players involved in tolerance to drought. Sugars Will Eventually be Exported Transporters (SWEETs) facilitate both the influx and efflux of mono- and/or disaccharides and control both inter and intracellular distribution of sugars. PagSWEET17a in Populus alba × P. glandulosa is one of four orthologous genes of AtSWEET17 in Arabidopsis. Unlike AtSWEET17, which is a vacuolar localized transporter, PagSWEET17a is localized to the endoplasmic reticulum (ER). Here, the role of PagSWEET17a in poplar responses to drought stress was investigated. PagSWEET17a was specifically expressed in cambium cells in younger root but mainly located in phloem fibers, and xylem vessels and fiber cells in the root undergoing secondary growth. Loss of PagSWEET17a inhibited the growth of roots in poplar seedlings and led to a decreased tolerance to drought. Analysis of sugar profiles revealed that accumulations of predominant sugars were significantly suppressed in both knockout (KO) mutant lines under drought. PagSWEET17a might contribute to poplar tolerance to drought by promoting drought-induced root expansion and diminishing oxidative damages caused by the stress. [ABSTRACT FROM AUTHOR]

Main conclusion: OsTST1 affects yield and development and mediates sugar transportation of plants from source to sink in rice, which influences the accumulation of intermediate metabolites from tricarboxylic acid cycle indirectly. Tonoplast sugar transporters (TSTs) are essential for vacuolar sugar accumulation in plants. Carbohydrate transport across tonoplasts maintains the metabolic balance in plant cells, and carbohydrate distribution is crucial to plant growth and productivity. Large plant vacuoles store high concentrations of sugars to meet plant requirements for energy and other biological processes. The abundance of sugar transporter affects crop biomass and reproductive growth. However, it remains unclear whether the rice (Oryza sativa L.) sugar transport protein OsTST1 affects yield and development. In this study, we found that OsTST1 knockout mutants generated via CRISPR/Cas9 exhibited slower development, smaller seeds, and lower yield than wild type (WT) rice plants. Notably, plants overexpressing OsTST1 showed the opposite effects. Changes in rice leaves at 14 days after germination (DAG) and at 10 days after flowering (DAF) suggested that OsTST1 affected the accumulation of intermediate metabolites from the glycolytic pathway and the tricarboxylic acid (TCA) cycle. The modification of the sugar transport between cytosol and vacuole mediated by OsTST1 induces deregulation of several genes including transcription factors (TFs). In summary, no matter the location of sucrose and sink is, these preliminary results revealed that OsTST1 was important for sugar transport from source to sink tissues, thus affecting plant growth and development. [ABSTRACT FROM AUTHOR]

Glycoside hydrolases (GHs) are carbohydrate-active enzymes essential for many environmental (e.g., carbon cycling) and biotechnological (e.g., biofuels) processes. The complete processing of carbohydrates by bacteria requires many enzymes acting synergistically. Here, I investigated the clustered or scattered distribution of 406,337 GH-genes and their association with transporter genes identified in 15,640 completely sequenced bacterial genomes. Different bacterial lineages displayed conserved levels of clustered or scattered GH-genes, but overall, the GH-genes clustering was generally higher than in randomized genomes. In lineages with highly clustered GH-genes (e.g., Bacteroides, Paenibacillus), clustered genes shared the same orientation. These codirectional gene clusters potentially facilitate the genes' co-expression by allowing transcriptional read-through and, at least in some cases, forming operons. In several taxa, the GH-genes clustered with distinct types of transporter genes. The type of transporter genes and the distribution of the so-called GH:TR-genes clusters were conserved in selected lineages. Globally, the phylogenetically conserved clustering of the GH-genes with transporter genes highlights the central function of carbohydrate processing across bacterial lineages. In addition, in bacteria with the most identified GH-genes, the genomic adaptations for carbohydrate processing also mirrored the broad environmental origin of the sequenced strains (e.g., soil and mammal gut) suggesting that a combination of evolutionary history and the environment selects for the specific supragenic organization of the GH-genes supporting the carbohydrate processing in bacterial genomes. [ABSTRACT FROM AUTHOR]

Sugar transporters are essential for osmotic process regulation, various signaling pathways and plant growth and development. Currently, few studies are available on the function of sugar transporters in sorghum (Sorghum bicolor L.). In this study, we performed a genome-wide survey of sugar transporters in sorghum. In total, 98 sorghum sugar transporters (SSTs) were identified via BLASTP. These SSTs were classified into three families based on the phylogenetic and conserved domain analysis, including six sucrose transporters (SUTs), 23 sugars will eventually be exported transporters (SWEETs), and 69 monosaccharide transporters (MSTs). The sorghum MSTs were further divided into seven subfamilies, including 24 STPs, 23 PLTs, two VGTs, four INTs, three pGlcT/SBG1s, five TMTs, and eight ERDs. Chromosomal localization of the SST genes showed that they were randomly distributed on 10 chromosomes, and substantial clustering was evident on the specific chromosomes. Twenty-seven SST genes from the families of SWEET, ERD, STP, and PLT were found to cluster in eight tandem repeat event regions. In total, 22 SSTs comprising 11 paralogous pairs and accounting for 22.4% of all the genes were located on the duplicated blocks. The different subfamilies of SST proteins possessed the same conserved domain, but there were some differences in features of the motif and transmembrane helices (TMH). The publicly-accessible RNA-sequencing data and real-time PCR revealed that the SST genes exhibited distinctive tissue specific patterns. Functional studies showed that seven SSTs were mainly located on the cell membrane and membrane organelles, and 14 of the SSTs could transport different types of monosaccharides in yeast. These findings will help us to further elucidate their roles in the sorghum sugar transport and sugar signaling pathways.

Cell wall polysaccharides play key roles in fungal development, virulence, and resistance to the plant immune system, and are synthesized from many nucleotide sugars in the endoplasmic reticulum (ER)‐Golgi secretory system. Nucleotide sugar transporters (NSTs) are responsible for transporting cytosolic‐derived nucleotide sugars to the ER lumen for processing, but their roles in plant‐pathogenic fungi remain to be revealed. Here, we identified two important NSTs, NST1 and NST2, in the rice blast fungus Magnaporthe oryzae. Both NSTs were localized in the ER, which was consistent with a function in transporting nucleotide sugar for processing in the ER. Sugar transport property analysis suggested that NST1 is involved in transportation of mannose and glucose, while NST2 is only responsible for mannose transportation. Accordingly, deletion of NSTs resulted in a significant decrease in corresponding soluble saccharides abundance and defect in sugar utilization. Moreover, both NSTs played important roles in cell wall integrity, were involved in asexual development, and were required for full virulence. The NST mutants exhibited decreasing external glycoproteins and exposure of inner chitin, which resulted in activation of the host defence response. Altogether, our results revealed that two sugar transporters are required for fungal cell wall polysaccharides accumulation and full virulence of M. oryzae. [ABSTRACT FROM AUTHOR]

Summary: More than half of the world's food is provided by cereals, as humans obtain >60% of daily calories from grains. Producing more carbohydrates is always the final target of crop cultivation. The carbohydrate partitioning pathway directly affects grain yield, but the molecular mechanisms and biological functions are poorly understood, including rice (Oryza sativa L.), one of the most important food sources. Here, we reported a prolonged grain filling duration mutant 1 (gfd1), exhibiting a long grain‐filling duration, less grain number per panicle and bigger grain size without changing grain weight. Map‐based cloning and molecular biological analyses revealed that GFD1 encoded a MATE transporter and expressed high in vascular tissues of the stem, spikelet hulls and rachilla, but low in the leaf, controlling carbohydrate partitioning in the stem and grain but not in the leaf. GFD1 protein was partially localized on the plasma membrane and in the Golgi apparatus, and was finally verified to interact with two sugar transporters, OsSWEET4 and OsSUT2. Genetic analyses showed that GFD1 might control grain‐filling duration through OsSWEET4, adjust grain size with OsSUT2 and synergistically modulate grain number per panicle with both OsSUT2 and OsSWEET4. Together, our work proved that the three transporters, which are all initially classified in the major facilitator superfamily family, could control starch storage in both the primary sink (grain) and temporary sink (stem), and affect carbohydrate partitioning in the whole plant through physical interaction, giving a new vision of sugar transporter interactome and providing a tool for rice yield improvement. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass is a renewable raw material for producing several high-value-added chemicals and fuels. In general, xylose and glucose are the major sugars in biomass hydrolysates, and their efficient utilization by microorganisms is critical for an economical production process. Yeasts capable of co-consuming mixed sugars might lead to higher yields and productivities in industrial fermentation processes. Herein, we performed adaptive evolution assays with two xylose-fermenting yeasts, Spathaspora passalidarum and Scheffersomyces stipitis, to obtain derived clones with improved capabilities of glucose and xylose co-consumption. Adapted strains were obtained after successive growth selection using xylose and the non-metabolized glucose analog 2-deoxy-D-glucose as a selective pressure. The co-fermentation capacity of evolved and parental strains was evaluated on xylose-glucose mixtures. Our results revealed an improved co-assimilation capability by the evolved strains; however, xylose and glucose consumption were observed at slower rates than the parental yeasts. Genome resequencing of the evolved strains revealed genes affected by non-synonymous variants that might be involved with the co-consumption phenotype, including the HXT2.4 gene that encodes a putative glucose transporter in Sp. passalidarum. Expression of this mutant HXT2.4 in Saccharomyces cerevisiae improved the cells' co-assimilation of glucose and xylose. Therefore, our results demonstrated the successful improvement of co-fermentation through evolutionary engineering and the identification of potential targets for further genetic engineering of different yeast strains. Key points: • Laboratory evolution assay was used to obtain improved sugar co-consumption of non-Saccharomyces strains. • Evolved Sp. passalidarum and Sc. stipitis were able to more efficiently co-ferment glucose and xylose. • A mutant Hxt2.4 permease, which co-transports xylose and glucose, was identified. [ABSTRACT FROM AUTHOR]

Sugar transporters play an important role in the cellulase production of lignocellulose-degrading fungi. Nevertheless, the role and function of these transporters are still unclear. Here we first report intracellular sugar transporters assisting cellulase production in Trichoderma reesei (T. reesei) using lactose. The mRNA levels of sugar transporter genes mfs, gst, and lac1 were substantially upregulated in T. reesei cultivated on lactose, with the most abundant mRNA levels at 24 h as compared to glucose. Moreover, the individual deletion of these sugar transporters significantly inhibited cellulase production, solid cell growth, and sporulation of T. reesei, suggesting they play a supporting role in cellulase production when grown in lactose. Surprisingly, MFS, GST, and LAC1 were mainly localized in the cytoplasm, with MFS and LAC1 in the endoplasmic reticulum (ER), representing the first discovery of intracellular sugar transporters involved in cellulase biosynthesis in lactose culture. The absence of the gene lac1 noticeably inhibited most of the crucial genes related to cellulase production, including cellulase-encoding genes, transcription factors, and sugar transporters, at 24 h, which was fully relieved at 48 h or 72 h, indicating that lac1 affects cellulase production more at the early step. This research advances the understanding of the function of intracellular sugar transporters in fungi, particularly for fungal cellulase production. [ABSTRACT FROM AUTHOR]

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The genetic basis of phenotypic variation is a long-standing concern of evolutionary biology. Coloration has proven to be a visual, easily quantifiable, and highly tractable system for genetic analysis and is an ever-evolving focus of biological research. Compared with the homogenized brown-yellow cocoons of wild silkworms, the cocoons of domestic silkworms are spectacularly diverse in color, such as white, green, and yellow-red; this provides an outstanding model for exploring the phenotypic diversification and biological coloration. Herein, the molecular mechanism underlying silkworm green cocoon formation was investigated, which was not fully understood. We demonstrated that five of the seven members of a sugar transporter gene cluster were specifically duplicated in the Bombycidae and evolved new spatial expression patterns predominantly expressed in silk glands, accompanying complementary temporal expression; they synergistically facilitate the uptake of flavonoids, thus determining the green cocoon. Subsequently, polymorphic cocoon coloring landscape involving multiple loci and the evolution of cocoon color from wild to domestic silkworms were analyzed based on the pan-genome sequencing data. It was found that cocoon coloration involved epistatic interaction between loci; all the identified cocoon color-related loci existed in wild silkworms; the genetic segregation, recombination, and variation of these loci shaped the multicolored cocoons of domestic silkworms. This study revealed a new mechanism for flavonoids-based biological coloration that highlights the crucial role of gene duplication followed by functional diversification in acquiring new genetic functions; furthermore, the results in this work provide insight into phenotypic innovation during domestication. [ABSTRACT FROM AUTHOR]

Wood is recognized as the primary storage tissue in trees. During the process of wood formation, the xylem actively assimilates carbon from photosynthetic tissues to satisfy its developmental requirements. The photosynthetic product, sucrose, provides precursors and energy for cell wall synthesis, and its transportation significantly impacts the yield and quality of wood. The radial transport is a critical step in the accumulation of photosynthetic products to xylem, yet research on the involved sugar transporters and their roles remains limited. In the present study, PagSWEET17a , a sugar transporter gene with pronounced expression in the xylem, was examined for its expression pattern, substrate specificity, subcellular localization, and the consequential effects on wood formation. The present findings revealed that PagSWEET17a exhibited specificity for sucrose transport, and has triple subcellular localizations, including the plasma membrane, tonoplast, and endoplasmic reticulum membrane. PagSWEET17a expressed in the phloem cells of the stem, as well as in the developing xylem vessels and fiber cells, suggesting its potential involvement in various steps of radial transport. By mediating the accumulation of carbon in the xylem, PagSWEET17a influenced the width of the xylem, as well as the thickness and composition of the secondary cell walls in xylem cells. These insights contribute to a deeper understanding of the molecular mechanisms underlying wood formation and highlight the importance of sugar transporters in this process. • PagSWEET17a is expressed in phloem cells and developing xylem cells. • PagSWEET17a mediates sucrose radial transport in xylem. • Mutation of PagSWEET17a leads to a reduction in the xylem area. • PagSWEET17a influences the thickness and composition of the secondary cell walls. [ABSTRACT FROM AUTHOR]

GLUT7 is a Class II glucose transporter predominantly expressed at the apical membrane of enterocytes in the small intestine. Here, we report the cryo-EM structure of nanodisc-reconstituted human GLUT7 in the apo state at 3.3 Å resolution. Our atomic model reveals a typical major facilitator superfamily fold, with the substrate-binding site open to the extracellular side of the membrane. Despite the nearly identical conformation to its closest family member, rat GLUT5, our structure unveils distinct features of the substrate-binding cavity that may influence substrate specificity and binding mode. A homology model of the inward-open human GLUT7 indicates that similar to other members of the GLUT family, it may undergo a global rocker-switch-like reorientation of the transmembrane bundles to facilitate substrate translocation across the membrane. Our work enhances the current structural understanding of the GLUT family, and lays a foundation for rational design of regulators of GLUTs and other sugar transporters. • The cryo-EM structure of human GLUT7 was determined at 3.3 Å resolution. • GLUT7 is stabilized in the outward-facing conformation in the absence of substrate. • The structure provides valuable insight into the substrate-binding site. • The structure facilitates structure-based discovery of GLUT-targeted drugs. • Drugs with high potency, selectivity, and favorable pharmacokinetics may result. [ABSTRACT FROM AUTHOR]

Sugar transportation and sugar-to-starch metabolism are considered important processes in seed development and embryo viability. A few plant SWEET proteins acting as sugar transporters have been reported to function in inflorescence and/or seed development. Here, we identified seven members of the 21 OsSWEET genes in rice that play essential roles in sugar transportation and sugar-to-starch conversion in seed development. Nineteen OsSWEET genes exhibiting different expression patterns during inflorescence and seed development were knocked out individually by CRISPR/Cas9. One third of the mutants showed decreased fertile pollen viability and shriveled mature caryopses, resulting in weakened seed traits. Grain fill-related genes but not representative grain shape-regulating genes showed attenuated expression in the mutants. Seed of each of these mutants accumulated more sucrose, glucose or fructose but less starch. Among all OsSWEET genes, OsSWEET4 and OsSWEET11 had major effects on caryopsis development. The sugar-to-starch metabolic pathway was significantly altered in ossweet11 mutants based on differential expression analysis in RNA sequencing assays, confirming that OsSWEET11 functions as a sugar transporter with a key role in seed development. These results help to decipher the multiple functions of OsSWEET genes and to show how they might be used in genetic improvement of rice.

Introduction: Verticillium wilt (VW) caused by Verticillium dahliae is a soil-borne vascular fungal disease that severely affects cotton yield and fiber quality. Sugar metabolism plays an important role in the growth and pathogenicity of V. dahliae. However, limited information is known about the sugar transporter genes and their roles in the growth and pathogenicity of V. dahliae. Method: In this study, genome-wide identification of sugar transporter genes in V. dahliae was conducted and the expression profiles of these genes in response to root exudates from cotton varieties susceptible or resistant to V. dahliae were investigated based on RNA-seq data. Tobacco Rattle Virus-based host-induced gene silencing (TRV-based HIGS) and artificial small interfering RNAs (asiRNAs) were applied to investigate the function of candidate genes involved in the growth and pathogenic process of V. dahliae. Results: A total of 65 putative sugar transporter genes were identified and clustered into 8 Clades. Of the 65 sugar transporter genes, 9 were found to be induced only by root exudates from the susceptible variety, including VdST3 and VdST12 that were selected for further functional study. Silencing of VdST3 or VdST12 in host plants by TRV-based HIGS reduced fungal biomass and enhanced cotton resistance against V. dahliae. Additionally, silencing of VdST12 and VdST3 by feeding asiRNAs targeting VdST12 (asiR815 or asiR1436) and VdST3 (asiR201 or asiR1238) inhibited fungal growth, exhibiting significant reduction in hyphae and colony diameter, with a more significant effect observed for the asiRNAs targeting VdST12. The inhibitory effect of asiRNAs on the growth of V. dahliae was enhanced with the increasing concentration of asiRNAs. Silencing of VdST12 by feeding asiR815+asiR1436 significantly decreased the pathogenicity of V. dahliae. Discussion: The results suggest that VdST3 and VdST12 are sugar transporter genes required for growth and pathogenicity of V. dahliae and that asiRNA is a valuable tool for functional characterization of V. dahliae genes. [ABSTRACT FROM AUTHOR]

Soluble sugars are an important determinant of fruit taste, but their accumulation mechanisms remain elusive. In this study, we report two vacuolar invertase inhibitor genes involved in sugar accumulation in peach, PpINHa and PpINH3. Transient overexpression of PpINH3 in peach fruits resulted in an increase in sugar content, while the opposite trend was detected for PpINHa. Unexpectedly, PpINH3 and PpINHa both had no physical interaction with vacuolar invertase (VIN). Moreover, the PpVIN genes had no or extremely low expression in fruits at the ripening stage. These results suggested that the regulatory role of PpINHa and PpINH3 in sugar accumulation is unlikely due to their interaction with PpVINs. Additionally, overexpression of PpINHa and PpINH3 had an impact on transcription of genes related to fruit sugar metabolism and transport, which is likely responsible for their regulatory role in fruit sugar accumulation. Altogether, these results indicated an important role of PpINHs in fruit accumulation in peach. Our study provides new insights into molecular mechanisms underlying sugar accumulation, which could be useful for genetic improvement of fruit taste in breeding programs of peach and other fruit crops. [ABSTRACT FROM AUTHOR]

Sugar transport and distribution plays an important role in lily bulb development and resistance to abiotic stresses. In this study, a member of the Sugar Will Eventually be Exported Transporters (SWEET) gene family, LoSWEET14, from Oriental hybrid lily 'Sorbonne' was identified. LoSWEET14 encodes a protein of 278 amino acids and is capable of transporting sucrose and some types of hexoses. The transcript level of the LoSWEET14 gene was significantly increased under various stress conditions including drought, cold, salt stresses, and abscisic acid (ABA) treatment. Overexpression of LoSWEET14 in tobacco (Nicotiana tabacum) showed that the transgenic lines had larger leaves, accumulated more soluble sugars, and were more resistant to drought, cold, and salt stresses, while becoming more sensitive to ABA compared with wild-type lines. Promoter analysis revealed that multiple stress-related cis-acting elements were found in the promoter of LoSWEET14. According to the distribution of cis-acting elements, different lengths of 5′-deletion fragments were constructed and the LoSWEET14-pro3(-540 bp) was found to be able to drive GUS gene expression in response to abiotic stresses and ABA treatment. Furthermore, a yeast one hybrid (Y1H) assay proved that the AREB/ABF (ABRE-binding protein/ABRE-binding factor) from lilies (LoABF2) could bind to the promoter of LoSWEET14. These findings indicated that LoSWEET14 is induced by LoABF2 to participate in the ABA signaling pathway to promote soluble sugar accumulation in response to multiple abiotic stresses. [ABSTRACT FROM AUTHOR]

To investigate the role of the sugar transporter MAL31 on pullulan biosynthesis, the coding gene mal31 was respectively disrupted and overexpressed in the parental strain A. pullulans CCTCC M 2012259 to construct mutants of A. pullulans Δ mal31 and A. pullulans Mal31. Batch pullulan production significantly decreased by 69.1 % in A. pullulans Δ mal31 but increased by 15.9 % in A. pullulans Mal31 , as compared to the parental strain. We performed kinetics analysis, assays of key enzymes, determination of intracellular UDPG, NADH, and ATP contents, and measurement of transcriptional levels of genes associated with pullulan biosynthesis and excretion. The results confirmed that the mal31 disruption decreased the glucose consumption rate, decreased the formation rate and titer of pullulan, but increased the intracellular UDPG supply for β -glucan accumulation. In contrast, the mal31 overexpression increased the transcriptional levels of genes associated with pullulan biosynthesis, and accelerated the rates of glucose consumption and pullulan formation, thereby increased pullulan production. Our findings revealed that MAL31 is involved in the transport of precursors for pullulan biosynthesis. This study provides an accurate operating site for genetic modification of A. pullulans for improving pullulan production and also presents a feasible technique route for the overproduction of other polysaccharides. • The mal31 disruption decreased pullulan production but favored β -glucan formation. • The mal31 overexpression increased both UDPG supply and pullulan production. • MAL31 is involved in transmembrane transport of precursors for pullulan biosynthesis. [ABSTRACT FROM AUTHOR]