Cell wall invertase 3 plays critical roles in providing sugars during pollination and fertilization in cucumber

In plants, pollen-pistil interactions during pollination and fertilization mediate pollen hydration and germination, pollen tube growth, and seed set and development. Cell wall invertases (CWINs) help provide the carbohydrates for pollen development; however, their roles in pollination and fertilization have not been well established. In cucumber (Cucumis sativus), CsCWIN3 showed the highest expression in flowers, and we further examined CsCWIN3 for functions during pollination to seed set. Both CsCWIN3 transcript and CsCWIN3 protein exhibited similar expression patterns in the sepals, petals, stamen filaments, anther tapetum, and pollen of male flowers, as well as in the stigma, style, transmitting tract, and ovule funiculus of female flowers. Notably, repression of CsCWIN3 in cucumber did not affect the formation of parthenocarpic fruit but resulted in an arrested growth of stigma integuments in female flowers and a partially delayed dehiscence of anthers with decreased pollen viability in male flowers. Consequently, the pollen tube grew poorly in the gynoecia after pollination. In addition, CsCWIN3-RNAi (RNA interference) plants also showed affected seed development. Considering that sugar transporters could function in cucumber fecundity, we highlight the role of CsCWIN3 and a potential close collaboration between CWIN and sugar transporters in these processes. Overall, we used molecular and physiological analyses to determine the CsCWIN3-mediated metabolism during pollen formation, pollen tube growth, and plant fecundity. CsCWIN3 has essential roles from pollination and fertilization to seed set but not parthenocarpic fruit development in cucumber.

Orchids acquire fungal carbon for seed germination: pathways and players

To germinate in nature, orchid seeds strictly rely on seed germination-promoting orchid mycorrhizal fungi (sgOMFs) for provision of carbon nutrients. The underlying delivery pathway, however, remains elusive. We develop here a plausible model for sugar transport from sgOMFs to orchid embryonic cells to fuel germination. Orchids exploit sgOMFs to induce the formation of pelotons, elaborate intracellular hyphal coils in orchid embryos. The colonized orchid cells then obtain carbon nutrients by uptake from living hyphae and peloton lysis, primarily as glucose derived from fungal trehalose hydrolyzed by orchid-specific trehalases. The uptake of massive fungally derived glucose is likely to be mediated by two classes of membrane proteins, namely, sugars will eventually be exported transporters (SWEETs) and H+-hexose symporters. The proposed model serves as a launch pad for further research to better understand and improve orchid seed germination and conservation.

Safety evaluation of the food enzyme β-fructofuranosidase from the non-genetically modified Saccharomyces cerevisiae strain NCYC R693

The food enzyme β-fructofuranosidase (β-d-fructofuranoside fructohydrolase; EC 3.2.1.26) is produced with the non-genetically modified Saccharomyces cerevisiae strain NCYC R693 by Kerry Ingredients & Flavours Ltd. The production strain meets the requirements for the qualified presumption of safety (QPS) approach. The food enzyme is intended to be used in four food manufacturing processes. The dietary exposure to the food enzyme-total organic solids (TOS) was estimated to be up to 2.485 mg TOS/kg body weight per day in European populations. As the production strain qualifies for the QPS approach of safety assessment and no issue of concern arising from the production process of the food enzyme were identified, the Panel considered that no toxicological studies other than the assessment of allergenicity were necessary. A search for the similarity of the amino acid sequence of the food enzyme to known allergens was made and one match with a tomato allergen was found. The Panel considered that the risk of allergic reactions upon dietary exposure to this food enzyme, particularly in individuals sensitised to tomato, cannot be excluded. However, the likelihood of allergic reactions is expected not to exceed the likelihood of allergic reactions to tomato. Based on the data provided, the Panel concluded that this food enzyme does not give rise to safety concerns under the intended conditions of use.

Structure and Expression Analysis of PtrSUS, PtrINV, PtrHXK, PtrPGM, and PtrUGP Gene Families in Populus trichocarpa Torr. and Gray

Exogenous nitrogen and carbon can affect plant cell walls, which are composed of structural carbon. Sucrose synthase (SUS), invertase (INV), hexokinase (HXK), phosphoglucomutase (PGM), and UDP-glucose pyrophosphorylase (UGP) are the key enzymes of sucrose metabolism involved in cell wall synthesis. To understand whether these genes are regulated by carbon and nitrogen to participate in structural carbon biosynthesis, we performed genome-wide identification, analyzed their expression patterns under different carbon and nitrogen treatments, and conducted preliminary functional verification. Different concentrations of nitrogen and carbon were applied to poplar (Populus trichocarpa Torr. and Gray), which caused changes in cellulose, lignin, and hemicellulose contents. In poplar, 6 SUSs, 20 INVs, 6 HXKs, 4 PGMs, and 2 UGPs were identified. Moreover, the physicochemical properties, collinearity, and tissue specificity were analyzed. The correlation analysis showed that the expression levels of PtrSUS3/5, PtrNINV1/2/3/5/12, PtrCWINV3, PtrVINV2, PtrHXK5/6, PtrPGM1/2, and PtrUGP1 were positively correlated with the cellulose content. Meanwhile, the knockout of PtrNINV12 significantly reduced the cellulose content. This study could lay the foundation for revealing the functions of SUSs, INVs, HXKs, PGMs, and UGPs, which affected structural carbon synthesis regulated by nitrogen and carbon, proving that PtrNINV12 is involved in cell wall synthesis.

IbINV Positively Regulates Resistance to Black Rot Disease Caused by Ceratocystis fimbriata in Sweet Potato

Black rot disease, caused by Ceratocystis fimbriata Ellis & Halsted, severely affects both plant growth and post-harvest storage of sweet potatoes. Invertase (INV) enzymes play essential roles in hydrolyzing sucrose into glucose and fructose and participate in the regulation of plant defense responses. However, little is known about the functions of INV in the growth and responses to black rot disease in sweet potato. In this study, we identified and characterized an INV-like gene, named IbINV, from sweet potato. IbINV contained a pectin methylesterase-conserved domain. IbINV transcripts were most abundant in the stem and were significantly induced in response to C. fimbriata, salicylic acid, and jasmonic acid treatments. Overexpressing IbINV in sweet potato (OEV plants) led to vigorous growth and high resistance to black rot disease, while the down-regulation of IbINV by RNA interference (RiV plants) resulted in reduced plant growth and high sensitivity to black rot disease. Furthermore, OEV plants contained a decreased sucrose content and increased hexoses content, which might be responsible for the increased INV activities; not surprisingly, RiV plants showed the opposite effects. Taken together, these results indicate that IbINV positively regulates plant growth and black rot disease resistance in sweet potato, mainly by modulating sugar metabolism.

Genome-Wide Identification and Expression Patterns of Cucumber Invertases and Their Inhibitor Genes

Invertases and their inhibitors play important roles in sucrose metabolism, growth and development, signal transduction, and biotic and abiotic stress tolerance in many plant species. However, in cucumber, both the gene members and functions of invertase and its inhibitor families remain largely unclear. In this study, in comparison with the orthologues of Citrullus lanatus (watermelon), Cucumis melo (melon), and Arabidopsis thaliana (Arabidopsis), 12 invertase genes and 12 invertase inhibitor genes were identified from the genome of Cucumis sativus (cucumber). Among them, the 12 invertase genes were classified as 4 cell wall invertases, 6 cytoplasmic invertases, and 2 vacuolar invertases. Most invertase genes were conserved in cucumber, melon, and watermelon, with several duplicate genes in melon and watermelon. Transcriptome analysis distinguished these genes into various expression patterns, which included genes CsaV3_2G025540 and CsaV3_2G007220, which were significantly expressed in different tissues, organs, and development stages, and genes CsaV3_7G034730 and CsaV3_5G005910, which might be involved in biotic and abiotic stress. Six genes were further validated in cucumber based on quantitative real-time PCR (qRT-PCR), and three of them showed consistent expression patterns as revealed in the transcriptome. These results provide important information for further studies on the physiological functions of cucumber invertases (CSINVs) and their inhibitors (CSINHs).

Regulatory and functional divergence among members of Ibβfruct2, a sweet potato vacuolar invertase gene controlling starch and glucose content

Sweet potato [Ipomoea batatas (L.) Lam.] is an important food and industrial crop. Its storage root is rich in starch, which is present in the form of granules and represents the principal storage carbohydrate in plants. Starch content is an important trait of sweet potato controlling the quality and yield of industrial products. Vacuolar invertase encoding gene Ibβfruct2 was supposed to be a key regulator of starch content in sweet potato, but its function and regulation were unclear. In this study, three Ibβfruct2 gene members were detected. Their promoters displayed differences in sequence, activity, and cis-regulatory elements and might interact with different transcription factors, indicating that the three Ibβfruct2 family members are governed by different regulatory mechanisms at the transcription level. Among them, we found that only Ibβfruct2-1 show a high expression level and promoter activity, and encodes a protein with invertase activity, and the conserved domains and three conserved motifs NDPNG, RDP, and WEC are critical to this activity. Only two and six amino acid residue variations were detected in sequences of proteins encoded by Ibβfruct2-2 and Ibβfruct2-3, respectively, compared with Ibβfruct2-1; although not within key motifs, these variations affected protein structure and affinities for the catalytic substrate, resulting in functional deficiency and low activity. Heterologous expression of Ibβfruct2-1 in Arabidopsis decreased starch content but increased glucose content in leaves, indicating Ibβfruct2-1 was a negative regulator of starch content. These findings represent an important advance in understanding the regulatory and functional divergence among duplicated genes in sweet potato, and provide critical information for functional studies and utilization of these genes in genetic improvement.

Differences in the Production of Extracellular Polymeric Substances (EPS) and Other Metabolites of Plenodomus (Leptosphaeria) Infecting Winter Oilseed Rape (Brassica napus L.)

Species of the genus Plenodomus (Leptosphaeria) are phytopathogens of the Brassicaceae family, which includes oilseed rape. The spores of these fungi spread by airborne transmission, infect plants, and cause crop losses. The secondary metabolism of P. lingam and P. biglobosus was studied and compared, with the main focus being on the ability to produce Extracellular Polymeric Substances (EPS). In spite of the 1.5-2-fold faster growth rate of P. biglobosus on Czapek-Dox and other screening media, the average yield of EPS in this fungus was only 0.29 g/L, compared to that of P. lingam (0.43 g/L). In turn, P. biglobosus showed a higher capacity to synthesise IAA, i.e., 14 µg/mL, in contrast to <1.5 µg/mL produced by P. lingam. On the other hand, the P. lingam strains showed higher β-glucanase activity (350-400 mU/mL), compared to 50-100 mU/mL in P. biglobosus. Invertase levels were similar in both species (250 mU/mL). The positive correlation between invertase activity and EPS yield contrasted with the absence of a correlation of EPS with β-glucanase. Plenodomus neither solubilised phosphate nor used proteins from milk. All strains showed the ability to synthesise siderophores on CAS agar. P. biglobosus exhibited the highest efficiency of amylolytic and cellulolytic activity.

Optimizing growth and biomass production of non-Saccharomyces wine yeast starters by overcoming sucrose consumption deficiency

The use of non-Saccharomyces yeasts as starters in winemaking has increased exponentially in the last years. For instance, non-conventional yeasts have proven useful for the improvement of the organoleptic profile and biocontrol. Active dry yeast starter production has been optimized for Saccharomyces cerevisiae, which may entail problems for the propagation of non-Saccharomyces yeasts. This work shows that the poor growth of Hanseniaspora vineae and Metschnikowia pulcherrima in molasses is related to a deficient sucrose consumption, linked to their low invertase activity. In order to address this issue, simple modifications to the cultivation media based hydrolysis and the reduction of sucrose concentration were performed. We performed biomass propagation simulations at a bench-top and bioreactor scale. The results show that cultivation in a hexose-based media improved biomass production in both species, as it solves their low invertase activity. The reduction in sugar concentration promoted a metabolic shift to a respiratory metabolism, which allowed a higher biomass yield, but did not improve total biomass production, due to the lower sugar availability. To evaluate the technological performance of these adaptations, we performed mixed grape juice fermentations with biomass produced in such conditions of M. pulcherrima and S. cerevisiae. The analysis of wines produced revealed that the different treatments we have tested did not have any negative impact on wine quality, further proving their applicability at an industrial level for the improvement of biomass production.

Genome-wide identification and analysis of the invertase gene family in tobacco (Nicotiana tabacum) reveals NtNINV10 participating the sugar metabolism

Sucrose (Suc) is directly associated with plant growth and development as well as tolerance to various stresses. Invertase (INV) enzymes played important role in sucrose metabolism by irreversibly catalyzing Suc degradation. However, genome-wide identification and function of individual members of the INV gene family in Nicotiana tabacum have not been conducted. In this report, 36 non-redundant NtINV family members were identified in Nicotiana tabacum including 20 alkaline/neutral INV genes (NtNINV1-20), 4 vacuolar INV genes (NtVINV1-4), and 12 cell wall INV isoforms (NtCWINV1-12). A comprehensive analysis based on the biochemical characteristics, the exon-intron structures, the chromosomal location and the evolutionary analysis revealed the conservation and the divergence of NtINVs. For the evolution of the NtINV gene, fragment duplication and purification selection were major factors. Besides, our analysis revealed that NtINV could be regulated by miRNAs and cis-regulatory elements of transcription factors associated with multiple stress responses. In addition, 3D structure analysis has provided evidence for the differentiation between the NINV and VINV. The expression patterns in diverse tissues and under various stresses were investigated, and qRT-PCR experiments were conducted to confirm the expression patterns. Results revealed that changes in NtNINV10 expression level were induced by leaf development, drought and salinity stresses. Further examination revealed that the NtNINV10-GFP fusion protein was located in the cell membrane. Furthermore, inhibition of the expression of NtNINV10 gene decreased the glucose and fructose in tobacco leaves. Overall, we have identified possible NtINV genes functioned in leaf development and tolerance to environmental stresses in tobacco. These findings provide a better understanding of the NtINV gene family and establish the basis for future research.

Heterologous expression of genes from a cyanobacterial endosymbiont highlights substrate exchanges with its diatom host

A few genera of diatoms are widespread and thrive in low-nutrient waters of the open ocean due to their close association with N₂-fixing, filamentous heterocyst-forming cyanobacteria. In one of these symbioses, the symbiont, Richelia euintracellularis, has penetrated the cell envelope of the host, Hemiaulus hauckii, and lives inside the host cytoplasm. How the partners interact, including how the symbiont sustains high rates of N₂ fixation, is unstudied. Since R. euintracellularis has evaded isolation, heterologous expression of genes in model laboratory organisms was performed to identify the function of proteins from the endosymbiont. Gene complementation of a cyanobacterial invertase mutant and expression of the protein in Escherichia coli showed that R. euintracellularis HH01 possesses a neutral invertase that splits sucrose producing glucose and fructose. Several solute-binding proteins (SBPs) of ABC transporters encoded in the genome of R. euintracellularis HH01 were expressed in E. coli, and their substrates were characterized. The selected SBPs directly linked the host as the source of several substrates, e.g. sugars (sucrose and galactose), amino acids (glutamate and phenylalanine), and a polyamine (spermidine), to support the cyanobacterial symbiont. Finally, transcripts of genes encoding the invertase and SBPs were consistently detected in wild populations of H. hauckii collected from multiple stations and depths in the western tropical North Atlantic. Our results support the idea that the diatom host provides the endosymbiotic cyanobacterium with organic carbon to fuel N₂ fixation. This knowledge is key to understanding the physiology of the globally significant H. hauckii-R. euintracellularis symbiosis.

Chilling induces sugar and ABA accumulation that antagonistically signals for symplastic connection of dormant potato buds

Endodormancy (ED) is a crucial stage in the life cycle of many perennial plants. ED release requires accumulating a certain amount of cold exposure, measured as chilling units. However, the mechanism governing the effect of chilling on ED duration is poorly understood. We used the potato tuber model to investigate the response to chilling as associated with ED release. We measured the accumulation of specific sugars during and after chilling, defined as sugar units. We discovered that ED duration correlated better with sugar units accumulation than chilling units. A logistic function was developed based on sugar units measurements to predict ED duration. Knockout or overexpression of the vacuolar invertase gene (StVInv) unexpectedly modified sugar units levels and extended or shortened ED, respectively. Silencing the energy sensor SNF1-related protein kinase 1, induced higher sugar units accumulation and shorter ED. Sugar units accumulation induced by chilling or transgenic lines reduced plasmodesmal (PD) closure in the dormant bud meristem. Chilling or knockout of abscisic acid (ABA) 8'-hydroxylase induced ABA accumulation, in parallel to sweetening, and antagonistically promoted PD closure. Our results suggest that chilling induce sugar units and ABA accumulation, resulting in antagonistic signals for symplastic connection of the dormant bud.

Safety evaluation of the food enzyme β-fructofuranosidase from the non-genetically modified Saccharomyces cerevisiae strain INV

The food enzyme β-fructofuranosidase (β-d-fructofuranoside fructohydrolase; EC 3.2.1.26) is produced with the non-genetically modified Saccharomyces cerevisiae strain INV by DSM Food Specialties B.V. It is intended to be used in four food manufacturing processes: manufacture of specialty carbohydrates (invert sugar syrups), baking processes, production of sucrose-based fermented beverages and confectionary processes. The dietary exposure to the food enzyme-total organic solids (TOS) was estimated to be up to 2.51 mg TOS/kg body weight (bw) per day in European populations. Toxicological studies were not considered necessary, given the qualified presumption of safety status of the production strain and the nature of the manufacturing process. A search for the similarity of the amino acid sequence of the food enzyme to known allergens was made and one match with a tomato allergen was found. The Panel considered that, under the intended conditions of use, the risk of allergic reactions upon dietary exposure to this food enzyme, particularly in individuals sensitised to tomato, cannot be excluded. However, the likelihood of allergic reactions to the β-fructofuranosidase from S. cerevisiae strain INV is expected not to exceed the likelihood of allergic reactions to tomato. As the prevalence of allergic reactions to tomato is low, also the likelihood of such reaction to occur to the food enzyme is low. Based on the data provided, the Panel concluded that this food enzyme does not give rise to safety concerns, under the intended conditions of use.

Contribution of Sucrose Metabolism in Phloem to Kiwifruit Bacterial Canker Resistance

Kiwifruit bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa), is a catastrophic disease affecting kiwifruit worldwide. As no effective cure has been developed, planting Psa-resistant cultivars is the best way to avoid bacterial canker in kiwifruit cultivation. However, the differences in the mechanism of resistance between cultivars is poorly understood. In the present study, five local kiwifruit cultivars were used for Psa resistance evaluation and classified into different resistance categories, tolerant (T), susceptible (S), and highly susceptible (HS), based on their various symptoms of lesions on the cane. Susceptible and highly susceptible varieties had a higher sucrose concentration, and a greater decrease in sucrose content was observed after Psa inoculation in phloem than in tolerant varieties. Three invertase activities and their corresponding gene expressions were detected in the phloem with lesions and showed the same trends as the variations in sucrose concentration. Meanwhile, after Psa inoculation, enzyme activities involved in antioxidant defense responses, such as PAL, POD, and CAT, were also altered in the phloem of the lesion position. With no differences among cultivars, PAL and POD activities in phloem first increased and then decreased after Psa inoculation. However, great differences in CAT activities were observed between T and S/HS categories. Our results demonstrate that sucrose content was negatively correlated with the disease resistance of different cultivars and that the increase in immune response enzymes is likely caused by increased sucrose metabolism in the phloem.

Characteristics and Expression Analysis of Invertase Gene Family in Common Wheat (Triticum aestivum L.)

Invertase (INV) irreversibly catalyzes the conversion of sucrose into glucose and fructose, playing important role in plant development and stress tolerance. However, the functions of INV genes in wheat have been less studied. In this study, a total of 126 TaINV genes were identified using a genome-wide search method, which could be classified into five classes (TaCWI-α, TaCWI-β, TaCI-α, TaCI-β, and TaVI) based on phylogenetic relationship. A total of 101 TaINVs were collinear with their ancestors in the synteny analysis, and we speculated that polyploidy events were the main force in the expansion of the TaINV gene family. Compared with TaCI, TaCWI and TaVI are more similar in gene structure and protein properties. Transcriptome sequencing analysis showed that TaINVs expressed in multiple tissues with different expression levels. Among 19 tissue-specific expressed TaINVs, 12 TaINVs showed grain-specific expression pattern and might play an important role in wheat grain development. In addition, qRT-PCR results further confirmed that TaCWI50 and TaVI27 show different expression in grain weight NILs. Our results demonstrated that the high expression of TaCWI50 and TaVI27 may be associated with a larger TGW phenotype. This work provides the foundations for understanding the grain development mechanism.

Two AT-Hook proteins regulate A/NINV7 expression to modulate sucrose catabolism for cold tolerance in Poncirus trifoliata

Invertase (INV)-mediated sucrose (Suc) hydrolysis, leading to the irreversible production of glucose (Glc) and fructose (Frc), plays an essential role in abiotic stress tolerance of plants. However, the regulatory network associated with the Suc catabolism in response to cold environment remains largely elusive. Herein, the cold-induced alkaline/neutral INV gene PtrA/NINV7 of trifoliate orange (Poncirus trifoliata (L.) Raf.) was shown to function in cold tolerance via mediating the Suc hydrolysis. Meanwhile, a nuclear matrix-associated region containing A/T-rich sequences within its promoter was indispensable for the cold induction of PtrA/NINV7. Two AT-Hook Motif Containing Nuclear Localized (AHL) proteins, PtrAHL14 and PtrAHL17, were identified as upstream transcriptional activators of PtrA/NINV7 by interacting with the A/T-rich motifs. PtrAHL14 and PtrAHL17 function positively in the cold tolerance by modulating PtrA/NINV7-mediated Suc catabolism. Furthermore, both PtrAHL14 and PtrAHL17 could form homo- and heterodimers between each other, and interacted with two histone acetyltransferases (HATs), GCN5 and TAF1, leading to elevated histone3 acetylation level under the cold stress. Taken together, our findings unraveled a new cold-responsive signaling module (AHL14/17-HATs-A/NINV7) for orchestration of Suc catabolism and cold tolerance, which shed light on the molecular mechanisms underlying Suc catabolism catalyzed by A/NINVs under cold stress.

Sugar conundrum in plant-pathogen interactions: roles of invertase and sugar transporters depend on pathosystems

It has been increasingly recognized that CWIN (cell wall invertase) and sugar transporters including STP (sugar transport protein) and SWEET (sugar will eventually be exported transporters) play important roles in plant-pathogen interactions. However, the information available in the literature comes from diverse systems and often yields contradictory findings and conclusions. To solve this puzzle, we provide here a comprehensive assessment of the topic. Our analyses revealed that the regulation of plant-microbe interactions by CWIN, SWEET, and STP is conditioned by the specific pathosystems involved. The roles of CWINs in plant resistance are largely determined by the lifestyle of pathogens (biotrophs versus necrotrophs or hemibiotrophs), possibly through CWIN-mediated salicylic acid or jasmonic acid signaling and programmed cell death pathways. The up-regulation of SWEETs and STPs may enhance or reduce plant resistance, depending on the cellular sites from which pathogens acquire sugars from the host cells. Finally, plants employ unique mechanisms to defend against viral infection, in part through a sugar-based regulation of plasmodesmatal development or aperture. Our appraisal further calls for attention to be paid to the involvement of microbial sugar metabolism and transport in plant-pathogen interactions, which is an integrated but overlooked component of such interactions.

Contrasting Strategies for Sucrose Utilization in a Floral Yeast Clade

Yeast species in the Wickerhamiella and Starmerella genera (W/S clade) thrive in the sugar-rich floral niche. We have previously shown that species belonging to this clade harbor an unparalleled number of genes of bacterial origin, among which is the SUC2 gene, encoding a sucrose-hydrolyzing enzyme. In this study, we used complementary in silico and experimental approaches to examine sucrose utilization in a broader cohort of species representing extant diversity in the W/S clade. Distinct strategies and modes of sucrose assimilation were unveiled, involving either extracellular sucrose hydrolysis through secreted bacterial Suc2 or intracellular assimilation using broad-substrate-range α-glucoside/H⁺ symporters and α-glucosidases. The intracellular pathway is encoded in two types of gene clusters reminiscent of the MAL clusters in Saccharomyces cerevisiae, where they are involved in maltose utilization. The genes composing each of the two types of MAL clusters found in the W/S clade have disparate evolutionary histories, suggesting that they formed de novo. Both transporters and glucosidases were shown to be functional and additionally involved in the metabolization of other disaccharides, such as maltose and melezitose. In one Wickerhamiella species lacking the α-glucoside transporter, maltose assimilation is accomplished extracellularly, an attribute which has been rarely observed in fungi. Sucrose assimilation in Wickerhamiella generally escaped both glucose repression and the need for an activator and is thus essentially constitutive, which is consistent with the abundance of both glucose and sucrose in the floral niche. The notable plasticity associated with disaccharide utilization in the W/S clade is discussed in the context of ecological implications and energy metabolism. IMPORTANCE Microbes usually have flexible metabolic capabilities and are able to use different compounds to meet their needs. The yeasts belonging to the Wickerhamiella and Starmerella genera (forming the so-called W/S clade) are usually found in flowers or insects that visit flowers and are known for having acquired many genes from bacteria by a process called horizontal gene transfer. One such gene, dubbed SUC2, is used to assimilate sucrose, which is one of the most abundant sugars in floral nectar. Here, we show that different lineages within the W/S clade used different solutions for sucrose utilization that dispensed SUC2 and differed in their energy requirements, in their capacity to scavenge small amounts of sucrose from the environment, and in the potential for sharing this resource with other microbial species. We posit that this plasticity is possibly dictated by adaptation to the specific requirements of each species.

Sugar, Invertase Enzyme Activities and Invertase Gene Expression in Different Developmental Stages of Strawberry Fruits

The cultivated strawberry (Fragaria × ananassa) is octoploid (2n = 8x = 56) and has been the focused fruit species of which an increasing number of molecular and genetic research has been conducted in recent years. The aim of this study is to identify the relationships between sucrose metabolism, invertase enzyme activity and gene expression in four different fruit development periods (red, pink, green and white) of two commercially important strawberry varieties 'Rubygem' and 'Fortuna'. The metabolite profiles (glucose, fructose, sucrose and total sugar content) of two varieties were discovered to be extremely similar. The highest amount of total sugar was found in red fruits, while the lowest was obtained from green fruits. Invertase represents one of the key enzymes in sucrose metabolism. The lowest invertase activity was obtained from the green fruits in 'Rubygem' and 'Fortuna' during four developmental periods. In these varieties, the amount of sucrose was found to be close to glucose and fructose and the lowest amount was detected in green period, while invertase activity was relatively high during red and pink periods and invertase gene expression was determined at high levels in both primers (St-4 and St-6) in the green period. The results of the study indicated that sugar content and invertase activity were positively correlated while enzyme activity and gene expression were negatively correlated.

Metabolic regulation of subcellular sucrose cleavage inferred from quantitative analysis of metabolic functions

Quantitative analysis of experimental metabolic data is frequently challenged by non-intuitive, complex patterns which emerge from regulatory networks. The complex output of metabolic regulation can be summarised by metabolic functions which comprise information about dynamics of metabolite concentrations. In a system of ordinary differential equations, metabolic functions reflect the sum of biochemical reactions which affect a metabolite concentration, and their integration over time reveals metabolite concentrations. Further, derivatives of metabolic functions provide essential information about system dynamics and elasticities. Here, invertase-driven sucrose hydrolysis was simulated in kinetic models on a cellular and subcellular level. Both Jacobian and Hessian matrices of metabolic functions were derived for quantitative analysis of kinetic regulation of sucrose metabolism. Model simulations suggest that transport of sucrose into the vacuole represents a central regulatory element in plant metabolism during cold acclimation which preserves control of metabolic functions and limits feedback-inhibition of cytosolic invertases by elevated hexose concentrations.

Optimization of β-Fructofuranosidase Production from Agrowaste by Aspergillus carbonarius and Its Application in the Production of Inverted Sugar

Research background

Microbial β-fructofuranosidases are widely employed in food industry to produce inverted sugar or fructooligosaccharides. In this study, a newly isolated Aspergillus carbonarius PC-4 strain was used to optimize the β-fructofuranosidase production in a cost-effective process and the sucrose hydrolysis was evaluated to produce inverted sugars.

Experimental approach

Optimization of nutritional components of culture medium was carried out using simplex lattice mixture design for 72 and 120 h at 28 °C. One-factor-at-a-time methodology was used to optimize the physicochemical parameters. Crude enzyme was used for sucrose hydrolysis at different concentrations.

Results and conclusions

The optimized conditions of enzyme production were achieved from cultivations containing pineapple crown waste (1.3%, m/V) and yeast extract (0.3%, m/V) after 72 h with an enzyme activity of 9.4 U/mL, obtaining R²=91.85%, R² _adjusted=85.06%, highest F-value (13.52) and low p-value (0.003). One-factor-at-a-time used for optimizing the physicochemical conditions showed optimum temperature (20 °C), pH (5.5), agitation (180 rpm) and time course (72 h) with a 3-fold increase of enzyme production. The invertase-induced sucrose hydrolysis showed the maximum yield (3.45 mmol of reducing sugars) using 10% of initial sucrose concentration. Higher sucrose concentrations caused the inhibition of invertase activity, possibly due to the saturation of substrate or formation of sucrose aggregates, making it difficult for the enzyme to access sucrose molecules within the created clusters. Therefore, a cost-effective method was developed for the invertase production using agroindustrial waste and the produced enzyme can be used efficiently for inverted sugar production at high sucrose concentration.

Novelty and scientific contribution

This study presents an efficient utilization of pineapple crown waste to produce invertase by a newly isolated Aspergillus carbonarius PC-4 strain. This enzyme exhibited a good potential for inverted sugar production at high initial sucrose concentration, which is interesting for industrial applications.

Identification and Expression Analyses of Invertase Genes in Moso Bamboo Reveal Their Potential Drought Stress Functions

Invertases (INVs) can irreversibly hydrolyze sucrose into fructose and glucose, which play principal roles in carbon metabolism and responses to various stresses in plants. However, little is known about the INV family in bamboos, especially their potential function in drought stress. In this study, 29 PeINVs were identified in moso bamboo (Phyllostachys edulis). They were clustered into alkaline/neutral invertase (NINV) and acid invertase (AINV) groups based on the gene structures, conserved motifs, and phylogenetic analysis results. The collinearity analysis showed nine segmental duplication pairs within PeINVs, and 25 pairs were detected between PeINVs and OsINVs. PeINVs may have undergone strong purification selection during evolution, and a variety of stress and phytohormone-related regulatory elements were found in the promoters of PeINVs. The tissue-specific expression analysis showed that PeINVs were differentially expressed in various moso bamboo tissues, which suggested that they showed functional diversity. Both the RNA-seq and quantitative real-time PCR results indicated that four PeINVs were significantly upregulated under drought stress. Co-expression network and Pearson’s correlation coefficient analyses showed that these PeINVs co-expressed positively with sugar and water transport genes (SWTGs), and the changes were consistent with sugar content. Overall, we speculate that the identified PeINVs are spatiotemporally expressed, which enables them to participate in moso bamboo growth and development. Furthermore, PeINVs, together with SWTGs, also seem to play vital roles in the response to drought stress. These results provide a comprehensive information resource for PeINVs, which will facilitate further study of the molecular mechanism underlying PeINVs involvement in the response to drought stress in moso bamboo.

Functional Characterization of a Cucumber (Cucumis sativus L.) Vacuolar Invertase, CsVI1, Involved in Hexose Accumulation and Response to Low Temperature Stress

Cucumber (Cucumis sativus L.), an important vegetable plant species, is susceptible to low temperature stress especially during the seedling stage. Vacuolar invertase (VI) plays important roles in plant responses to abiotic stress. However, the molecular and biochemical mechanisms of VI function in cucumber, have not yet been completely understood and VI responses to low temperature stress and it functions in cold tolerance in cucumber seedlings are also in need of exploration. The present study found that hexose accumulation in the roots of cucumber seedlings under low temperature stress is closely related to the observed enhancement of invertase activity. Our genome-wide search for the vacuolar invertase (VI) genes in cucumber identified the candidate VI-encoding gene CsVI1. Expression profiling of CsVI1 showed that it was mainly expressed in the young roots of cucumber seedlings. In addition, transcriptional analysis indicated that CsVI1 expression could respond to low temperature stress. Recombinant CsVI1 proteins purified from Pichia pastoris and Nicotiana benthamiana leaves could hydrolyze sucrose into hexoses. Further, overexpression of CsVI1 in cucumber plants could increase their hexose contents and improve their low temperature tolerance. Lastly, a putative cucumber invertase inhibitor was found could form a complex with CsVI1. In summary, these results confirmed that CsVI1 functions as an acid invertase involved in hexose accumulation and responds to low temperature stress in cucumber seedlings.

Optogenetic Tools for Control of Public Goods in Saccharomyces cerevisiae

Microorganisms live in dense and diverse communities, with interactions between cells guiding community development and phenotype. The ability to perturb specific intercellular interactions in space and time provides a powerful route to determining the critical interactions and design rules for microbial communities. Approaches using optogenetic tools to modulate these interactions offer promise, as light can be exquisitely controlled in space and time. We report new plasmids for rapid integration of an optogenetic system into Saccharomyces cerevisiae to engineer light control of expression of a gene of interest. In a proof-of-principle study, we demonstrate the ability to control a model cooperative interaction, namely, the expression of the enzyme invertase (SUC2) which allows S. cerevisiae to hydrolyze sucrose and utilize it as a carbon source. We demonstrate that the strength of this cooperative interaction can be tuned in space and time by modulating light intensity and through spatial control of illumination. Spatial control of light allows cooperators and cheaters to be spatially segregated, and we show that the interplay between cooperative and inhibitory interactions in space can lead to pattern formation. Our strategy can be applied to achieve spatiotemporal control of expression of a gene of interest in S. cerevisiae to perturb both intercellular and interspecies interactions.

IMPORTANCE Recent advances in microbial ecology have highlighted the importance of intercellular interactions in controlling the development, composition, and resilience of microbial communities. In order to better understand the role of these interactions in governing community development, it is critical to be able to alter them in a controlled manner. Optogenetically controlled interactions offer advantages over static perturbations or chemically controlled interactions, as light can be manipulated in space and time and does not require the addition of nutrients or antibiotics. Here, we report a system for rapidly achieving light control of a gene of interest in the important model organism Saccharomyces cerevisiae and demonstrate that by controlling expression of the enzyme invertase, we can control cooperative interactions. This approach will be useful for understanding intercellular and interspecies interactions in natural and synthetic microbial consortia containing S. cerevisiae and serves as a proof of principle for implementing this approach in other consortia.

A cell wall invertase controls nectar volume and sugar composition

Nectar volume and sugar composition are key determinants of the strength of plant-pollinator mutualisms. The main nectar sugars are sucrose, glucose and fructose, which can vary widely in ratio and concentration across species. Brassica spp. produce a hexose-dominant nectar (high in the monosaccharides glucose and fructose) with very low levels of the disaccharide sucrose. Cell wall invertases (CWINVs) catalyze the irreversible hydrolysis of sucrose into glucose and fructose in the apoplast. We found that BrCWINV4A is highly expressed in the nectaries of Brassica rapa. Moreover, a brcwinv4a null mutant: (i) has greatly reduced CWINV activity in the nectaries; (ii) produces a sucrose-rich nectar; but (iii) with significantly less volume. These results definitively demonstrate that CWINV activity is not only essential for the production of a hexose-rich nectar, but also support a hypothetical model of nectar secretion in which its hydrolase activity is required for maintaining a high intracellular-to-extracellular sucrose ratio that facilitates the continuous export of sucrose into the nectary apoplast. The extracellular hydrolysis of each sucrose into two hexoses by BrCWINV4A also likely creates the osmotic potential required for nectar droplet formation. These results cumulatively indicate that modulation of CWINV activity can at least partially account for naturally occurring differences in nectar volume and sugar composition. Finally, honeybees prefer nectars with some sucrose, but wild-type B. rapa flowers were much more heavily visited than flowers of brcwinv4a, suggesting that the potentially attractive sucrose-rich nectar of brcwinv4a could not compensate for its low volume.

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

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

Phloem loading in rice leaves depends strongly on the apoplastic pathway

Phloem loading is the first step in sucrose transport from source leaves to sink organs. The phloem loading strategy in rice remains unclear. To determine the potential phloem loading mechanism in rice, yeast invertase (INV) was overexpressed by a 35S promoter specifically in the cell wall to block sugar transmembrane loading in rice. The transgenic lines exhibited obvious phloem loading suppression characteristics accompanied by the accumulation of sucrose and starch, restricted vegetative growth and decreased grain yields. The decreased sucrose exudation rate with p-chloromercuribenzenesulfonic acid (PCMBS) treatment also indicated that rice actively transported sucrose into the phloem. OsSUT1 (SUCROSE TRANSPORTER 1) showed the highest mRNA levels of the plasma membrane-localized OsSUTs in source leaves. Cross sections of the OsSUT::GUS transgenic plants showed that the expression of OsSUT1 and OsSUT5 occurred in the phloem companion cells. Rice ossut1 mutants showed reduced growth and grain yield, supporting the hypothesis of OsSUT1 acting in phloem loading. Based on these results, we conclude that apoplastic phloem loading plays a major role in the export of sugar from rice leaves.

Structure and Expression Analysis of Sucrose Phosphate Synthase, Sucrose Synthase and Invertase Gene Families in Solanum lycopersicum

Sucrose phosphate synthase (SPS), sucrose synthase (SUS) and invertase (INV) are all encoded by multigene families. In tomato (Solanum lycopersicum), a comprehensive analysis of structure characteristics of these family genes is still lacking, and the functions of individual isoforms of these families are mostly unclear under stress. Here, the structure characteristics of the three families in tomato were analyzed; moreover, as a first step toward understanding the functions of isoforms of these proteins under stress, the tissue expression pattern and stress response of these genes were also investigated. The results showed that four SPS genes, six SUS genes and nineteen INV genes were identified in tomato. The subfamily differentiation of SlSPS and SlSUS might have completed before the split of monocotyledons and dicotyledons. The conserved motifs were mostly consistent within each protein family/subfamily. These genes demonstrated differential expressions among family members and tissues, and in response to polyethylene glycerol, NaCl, H₂O₂, abscisic acid or salicylic acid treatment. Our results suggest that each isoform of these families may have different functions in different tissues and under environmental stimuli. SlSPS1, SlSPS3, SlSUS1, SlSUS3, SlSUS4, SlINVAN5 and SlINVAN7 demonstrated consistent expression responses and may be the major genes responding to exogenous stimuli.

Identification of an Invertase With High Specific Activity for Raffinose Hydrolysis and Its Application in Soymilk Treatment

The hydrolyzation of raffinose into melibiose by using invertases under mild conditions improves the nutritional value of soybean products. However, this strategy has received little attention because a suitable invertase remains lacking. In this study, a novel invertase named InvDz13 was screened and purified from Microbacterium trichothecenolyticum and characterized. InvDz13 was one of the invertases with the highest specific activity toward raffinose. Specifically, it had a specific activity of 229 U/mg toward raffinose at pH 6.5 and 35°C. InvDz13 retained more than 80% of its maximum activity at pH 5.5–7.5 and 25–40°C and was resistant to or stimulated by most cations that presented in soymilk. In soymilk treated with InvDz13 under mild conditions, melibiose concentration increased from 3.1 ± 0.2 to 6.1 ± 0.1 mM due to raffinose hydrolyzation by InvDz13. Furthermore, the prebiotic property of InvDz13-treated soymilk was investigated via in vitro fermentation by human gut microbiota. Results showed that InvDz13 treatment increased the proportion of the beneficial bacteria Bifidobacterium and Lactobacillus by 1.6- and 3.7-fold, respectively. By contrast, the populations of Escherichia and Collinsella decreased by 1.8- and 11.7-fold, respectively. Thus, our results proved that the enzymatic hydrolysis of raffinose in soymilk with InvDz13 was practicable and might be an alternative approach to improving the nutritional value of soymilk.

Aerobic growth physiology of Saccharomyces cerevisiae on sucrose is strain-dependent

Present knowledge on the quantitative aerobic physiology of the yeast Saccharomyces cerevisiae during growth on sucrose as sole carbon and energy source is limited to either adapted cells or to the model laboratory strain CEN.PK113-7D. To broaden our understanding of this matter and open novel opportunities for sucrose-based biotechnological processes, we characterized three strains, with distinct backgrounds, during aerobic batch bioreactor cultivations. Our results reveal that sucrose metabolism in S. cerevisiae is a strain-specific trait. Each strain displayed distinct extracellular hexose concentrations and invertase activity profiles. Especially, the inferior maximum specific growth rate (0.21 h-1) of the CEN.PK113-7D strain, with respect to that of strains UFMG-CM-Y259 (0.37 h-1) and JP1 (0.32 h-1), could be associated to its low invertase activity (0.04-0.09 U/mgDM). Moreover, comparative experiments with glucose or fructose alone, or in combination, suggest mixed mechanisms of sucrose utilization by the industrial strain JP1, and points out the remarkable ability of the wild isolate UFMG-CM-259 to grow faster on sucrose than on glucose in a well-controlled cultivation system. This work hints to a series of metabolic traits that can be exploited to increase sucrose catabolic rates and bioprocess efficiency.

Cunninghamella echinulata PA3S12MM invertase: Biochemical characterization of a promiscuous enzyme

The Cunninghamella echinulata PA3S12MM fungus is a great producer of invertases in a growth medium supplemented by apple peels. The enzyme was purified 4.5 times after two chromatographic processes, and it presented a relative molecular mass of 89.2 kDa. The invertase reached maximum activity at pH of 6 and at 60°C, in addition to presenting stability in alkaline pH and thermal activation at 50°C. The enzymatic activity increased in the presence of Mn²⁺ and dithiothreitol (DTT), while Cu²⁺ and Z²⁺ ions inhibited it. Also, DTT showed to protect enzymatic activity. The apparent values for K_m , V_máx , and K_cat for the sucrose hydrolysis were, respectively, 173.8 mmol/L, 908.7 mmol/L min^-1 , and 1,388.79 s^-1 . The carbohydrate content was of 83.13%. The invertase presented hydrolytic activity over different types of glycosidic bonds, such as α1 ↔ 2β (sucrose), α1 → 4 (polygalacturonic acid), α1 → 4 and α1 → 2 (pectin), and α1 ↔ 1 (trehalose), indicating that the enzyme is multifunctional. Thus, the biochemical properties showed by the C. echinulata PA3S12MM suggest a broad industrial application, such as in the biomass hydrolysis or in the food industry. PRACTICAL APPLICATIONS: Invertases are hydrolytic enzymes employed in several industrial sectors. Given their great importance for the economy and several industrial sectors, there is a growing interest in microorganisms producing this enzyme. The analysis of the biochemical properties of invertase in C. echinulata PA3S12MM suggest applications in the food industry. Due to its increased hydrolytic activity, the hydrolysis process of the sucrose may employ invertase for the production of invert sugar. The stability at alkaline pH suggests an application in the development of enzymatic electrodes for the quantification of sucrose in food and beverage. The multifunctional activity may work in the biomass hydrolysis or saccharification of by-products for the extraction of fermentable sugars. The high level of invertase N-linked glycosylation of invertase grants this enzyme thermal stability at high temperatures, in addition to resistance against the action of proteases, which are desirable characteristics for the application of this enzyme in industrial processes.

Mucoromycotina Fungi Possess the Ability to Utilize Plant Sucrose as a Carbon Source: Evidence From Gongronella sp. w5

Mucoromycotina is one of the earliest fungi to establish a mutualistic relationship with plants in the ancient land. However, the detailed information on their carbon supply from the host plants is largely unknown. In this research, a free-living Mucoromycotina called Gongronella sp. w5 (w5) was employed to explore its effect on Medicago truncatula growth and carbon source utilization from its host plant during the interaction process. W5 promoted M. truncatula growth and caused the sucrose accumulation in M. truncatula root tissue at 16 days post-inoculation (dpi). The transportation of photosynthetic product sucrose to the rhizosphere by M. truncatula root cells seemed accelerated by upregulating the SWEET gene. A predicted cytoplasmic invertase (GspInv) gene and a sucrose transporter (GspSUT1) homology gene in the w5 genome upregulated significantly at the transcriptional level during w5–M. truncatula interaction at 16 dpi, indicating the possibility of utilizing plant sucrose directly by w5 as the carbon source. Further investigation showed that the purified GspInv displayed an optimal pH of 5.0 and a specific activity of 3380 ± 26 U/mg toward sucrose. The heterologous expression of GspInv and GspSUT1 in Saccharomyces cerevisiae confirmed the function of GspInv as invertase and GspSUT1 as sugar transporter with high affinity to sucrose in vivo. Phylogenetic tree analysis showed that the ability of Mucoromycotina to utilize sucrose from its host plant underwent a process of “loss and gain.” These results demonstrated the capacity of Mucoromycotina to interact with extant land higher plants and may employ a novel strategy of directly up-taking and assimilating sucrose from the host plant during the interaction.

Looking into 'hair tonics' for cotton fiber initiation

Cotton fiber is the most important source of cellulose for the global textile industry. These hair-like single-celled trichomes develop from ovule epidermis. They are classified into long spinnable lint and short fuzz. A key objective in the cotton industry is to breed elite cultivars with fuzzless seeds carrying high lint yield. Molecular basis underlying lint and fuzz initiation remains obscure. Recent studies indicate fiber initiation is under the control of MYB-bHLH-WDR (MBW) transcription factor complex. Based on molecular genetic studies and gene expression patterns linking fiber phenotypes, we propose that specific but different sets of MBW genes are required to precisely regulate the initiation of the lint and fuzz fibers. Emerging evidence further points to sugar signaling as a 'hair-tonic' to boost fiber initiation through interaction with MBW complex and auxin signaling. An integrative model is provided as a conceptual framework for future studies to dissect the molecular network responsible for cotton fiber initiation.

Transcriptomic Profiling of Populus Roots Challenged with Fusarium Reveals Differential Responsive Patterns of Invertase and Invertase Inhibitor-Like Families within Carbohydrate Metabolism

Fusarium solani (Fs) is one of the notorious necrotrophic fungal pathogens that cause root rot and vascular wilt, accounting for the severe loss of Populus production worldwide. The plant-pathogen interactions have a strong molecular basis. As yet, the genomic information and transcriptomic profiling on the attempted infection of Fs remain unavailable in a woody model species, Populus trichocarpa. We used a full RNA-seq transcriptome to investigate the molecular interactions in the roots with a time-course infection at 0, 24, 48, and 72 h post-inoculation (hpi) of Fs. Concomitantly, the invertase and invertase inhibitor-like gene families were further analyzed, followed by the experimental evaluation of their expression patterns using quantitative PCR (qPCR) and enzyme assay. The magnitude profiles of the differentially expressed genes (DEGs) were observed at 72 hpi inoculation. Approximately 839 genes evidenced a reception and transduction of pathogen signals, a large transcriptional reprogramming, induction of hormone signaling, activation of pathogenesis-related genes, and secondary and carbohydrate metabolism changes. Among these, a total of 63 critical genes that consistently appear during the entire interactions of plant-pathogen had substantially altered transcript abundance and potentially constituted suitable candidates as resistant genes in genetic engineering. These data provide essential clues in the developing new strategies of broadening resistance to Fs through transcriptional or translational modifications of the critical responsive genes within various analyzed categories (e.g., carbohydrate metabolism) in Populus.

Honey as a Functional Food for Apis mellifera

Although nectar is consumed, primarily as a supplemental food, by a broad range of insects spanning at least five orders, it is processed and stored by only a small number of species, most of which are bees and wasps in the superfamily Apoidea. Within this group, Apis mellifera has evolved remarkable adaptations facilitating nectar processing and storage; in doing so, this species utilizes the end product, honey, for diverse functions with few if any equivalents in other phytophagous insects. Honey and its phytochemical constituents, some of which likely derive from propolis, have functional significance in protecting honey bees against microbial pathogens, toxins, and cold stress, as well as in regulating development and adult longevity. The distinctive properties of A. mellifera honey appear to have arisen in multiple ways, including genome modification; partnerships with microbial symbionts; and evolution of specialized behaviors, including foraging for substances other than nectar. That honey making by A. mellifera involves incorporation of exogenous material other than nectar, as well as endogenous products such as antimicrobial peptides and royal jelly, suggests that regarding honey as little more than a source of carbohydrates for bees is a concept in need of revision.

Regulation of sugar metabolism genes in the nitrogen-dependent susceptibility of tomato stems to Botrytis cinerea

BACKGROUND AND AIMS

The main soluble sugars are important components of plant defence against pathogens, but the underlying mechanisms are unclear. Upon infection by Botrytis cinerea, the activation of several sugar transporters, from both plant and fungus, illustrates the struggle for carbon resources. In sink tissues, the metabolic use of the sugars mobilized in the synthesis of defence compounds or antifungal barriers is not fully understood.

METHODS

In this study, the nitrogen-dependent variation of tomato stem susceptibility to B. cinerea was used to examine, before and throughout the course of infection, the transcriptional activity of enzymes involved in sugar metabolism. Under different nitrate nutrition regimes, the expression of genes that encode the enzymes of sugar metabolism (invertases, sucrose synthases, hexokinases, fructokinases and phosphofructokinases) was determined and sugar contents were measured before inoculation and in asymptomatic tissues surrounding the lesions after inoculation.

KEY RESULTS

At high nitrogen availability, decreased susceptibility was associated with the overexpression of several genes 2 d after inoculation: sucrose synthases Sl-SUS1 and Sl-SUS3, cell wall invertases Sl-LIN5 to Sl-LIN9 and some fructokinase and phosphofructokinase genes. By contrast, increased susceptibility corresponded to the early repression of several genes that encode cell wall invertase and sucrose synthase. The course of sugar contents was coherent with gene expression.

CONCLUSIONS

The activation of specific genes that encode sucrose synthase is required for enhanced defence. Since the overexpression of fructokinase is also associated with reduced susceptibility, it can be hypothesized that supplementary sucrose cleavage by sucrose synthases is dedicated to the production of cell wall components from UDP-glucose, or to the additional implication of fructose in the synthesis of antimicrobial compounds, or both.

Genetically encoded multimode reporter of adaptor complex 3 traffic in budding yeast

AP-3 (adaptor complex 3) mediates traffic from the late Golgi or early endosomes to late endosomal compartments. In mammals, mutations in AP-3 cause Hermansky-Pudlak syndrome type 2, cyclic neutropenias, and a form of epileptic encephalopathy. In budding yeast, AP-3 carries cargo directly from the trans-Golgi to the lysosomal vacuole. Despite the pathway's importance and its discovery two decades ago, rapid screens and selections for AP-3 mutants have not been available. We now report GNSI, a synthetic, genetically encoded reporter that allows rapid plate-based assessment of AP-3 functional deficiency, using either chromogenic or growth phenotype readouts. This system identifies defects in both the formation and consumption of AP-3 carrier vesicles and is adaptable to high-throughput screening or selection in both plate array and liquid batch culture formats. Episomal and integrating plasmids encoding GNSI have been submitted to the Addgene repository.

Deletion of beta-fructofuranosidase (invertase) genes is associated with sucrose content in Date Palm fruit

The fruit of date palm trees are an important part of the diet for a large portion of the Middle East and North Africa. The fruit is consumed both fresh and dry and can be stored dry for extended periods of time. Date fruits vary significantly across hundreds of cultivars identified in the main regions of cultivation. Most dried date fruit are low in sucrose but high in glucose and fructose. However, high sucrose content is a distinctive feature of some date fruit and affects flavor as well as texture and water retention. To identify the genes controlling high sucrose content, we analyzed date fruit metabolomics for association with genotype data from 120 date fruits. We found significant association of dried date sucrose content and a genomic region that contains 3 tandem copies of the beta-fructofuranosidase (invertase) gene in the reference Khalas genome, a low-sucrose fruit. High-sucrose cultivars including the popular Deglet Noor had a homozygous deletion of two of the 3 copies of the invertase gene. We show the deletion allele is derived when compared to the ancestral allele that retains all copies of the gene in 3 other species of Phoenix. The fact that 2 of the 3 tandem invertase copies are associated with dry fruit sucrose content will assist in better understanding the distinct roles of multiple date palm invertases in plant physiology. Identification of the recessive alleles associated with end-point sucrose content in date fruit may be used in selective breeding in the future.

w5 for High Fructose Syrup Preparation

Invertases catalyze the hydrolysis of sucrose into fructose and glucose and can be employed as an alternative in producing high fructose syrup. In this study, we reported the heterologous expression of an invertase gene (GspInv) of Gongronella sp. w5 in Komagataella pastoris. GspInv activity reached 147.6 ± 0.4 U/mL after 5 days of methanol induction. GspInv is invertase with a high specific activity of 2,776.1 ± 124.2 U/mg toward sucrose. GspInv showed high tolerance to sucrose (IC 5 0 = 1.2 M), glucose (IC 5 0 > 2 M), fructose (IC 5 0 = 1.5 M), and a variety of metal ions that make it an ideal candidate for high fructose syrup production. A carbohydrate-binding module was sequence-optimized and fused to the N-terminus of GspInv. The fusion protein had the highest immobilization efficiency at room temperature within 1 h adsorption, with 1 g of cellulose absorption up to 8,000 U protein. The cellulose-immobilized fusion protein retained the unique properties of GspInv. When applied in high fructose syrup preparation by using 1 M sucrose as the substrate, the sucrose conversion efficiency of the fused protein remained at approximately 95% after 50 h of continuous hydrolysis on a packed bed reactor. The fused protein can also hydrolyze completely the sucrose in sugarcane molasses. Our results suggest that GspInv is an unusual invertase and a promising candidate for high fructose syrup preparation.

Transforming Candida hispaniensis, a promising oleaginous and flavogenic yeast

Candida hispaniensis is an oleaginous yeast with a great potential for production of single cell oil according to its naturally high lipid accumulation capacity. Its unusual small genome size trait is also attractive for fundamental research on genome evolution. Our physiological study suggests a great potential for lipid production, reaching 224 mg/g of cell dry weight in glucose minimum medium. C. hispaniensis is also able to secrete up to 34.6 mg/L of riboflavin promising further riboflavin production improvements by cultivation optimization and genetic engineering. However, while its genome sequence has been released very recently, no genetic tools have been described up to now for this yeast limiting its use for fundamental research and for exploitation in an industrial biotechnology. We report here the first genetic modification of C. hispaniensis by introducing a heterologous invertase allowing the growth on sucrose using a biolistic transformation approach using a dedicated vector. The first genetic tool and transformation method developed here appear as a proof of concept, and while it would benefit from further optimization, heterogeneous expression of invertase allows for metabolism of an additional sugar and shows heterologous enzyme production capacity.

Intervening in sibling competition for assimilates by controlled pollination prevents seed abortion under postpollination drought in maize

During maize production, drought throughout the flowering stage usually induces seed abortion and yield losses. The influence of postpollination drought stress on seed abortion and its underlying mechanisms are not well characterized. By intervening in the competition for assimilates between kernel siblings under different degrees of postpollination drought stresses accompanied by synchronous pollination (SP) and incomplete pollination (ICP) approaches, the mechanisms of postpollination abortion were investigated at physiological and molecular levels. Upon SP treatment, up to 15% of the fertilized apical kernels were aborted in the drought-exacerbated competition for assimilates. The aborted kernels exhibited weak sucrose hydrolysis and starch synthesis but promoted the synthesis of trehalose-6-phosphate and ethylene. In ICP where basal pollination was prevented, apical kernel growth was restored with reinstated sucrose metabolism and starch synthesis and promoted sucrose and hexose levels under drought stress. In addition, the equilibrium between ethylene and polyamine in response to the drought and pollination treatments was associated with the abortion process. We conclude that competition for assimilates drives postpollination kernel abortion, whereas differences in sugar metabolism and the equilibrium between ethylene and polyamines may be relevant to the "live or die" choice of kernel siblings during this competition.

Continuous Exposure to Ethylene Differentially Affects Senescence in Receptacle and Achene Tissues in Strawberry Fruit

Strawberry shelf life is limited, and little is known about the postharvest regulation of senescence in different fruit tissues. Strawberry is classified as a non-climacteric fruit, yet it is known that ethylene affects strawberry ripening. Here the effects of continuous exogenous ethylene (50 µl l^-1) were investigated in cold stored strawberry (5°C). The physiological and biochemical responses of ripe strawberry were evaluated across 6 days, together with hormonal profiles of the whole fruit and individual tissues (achenes and receptacle). Continuous exposure to ethylene induced as a first response an accumulation of abscisic acid (ABA) in the receptacle tissue, followed by an increase in CO₂ production. Ethylene also elicited sucrose hydrolysis and malic acid catabolism, with the major effect seen after 4 days of ethylene exposure. Additionally, accumulation of phenolics (epicatechin and chlorogenic acid) were also observed in ethylene treated strawberry. Achenes did not exhibit a response to ethylene, yet catabolism of both ABA and auxins increased by two thirds during air storage. In contrast, ethylene induced ABA accumulation in the receptacle tissue without ABA catabolism being affected. This hormonal disequilibrium in response to ethylene between the two tissues was maintained during storage, and therefore might be the precursor for the following biochemical variations reported during storage.

Liquid Chromatography Tandem Mass Spectrometry Quantification of 13C-Labeling in Sugars

Subcellular compartmentation has been challenging in plant ¹³C-metabolic flux analysis. Indeed, plant cells are highly compartmented: they contain vacuoles and plastids in addition to the regular organelles found in other eukaryotes. The distinction of reactions between compartments is possible when metabolites are synthesized in a particular compartment or by a unique pathway. Sucrose is an example of such a metabolite: it is specifically produced in the cytosol from glucose 6-phosphate (G6P) and fructose 6-phosphate (F6P). Therefore, determining the ¹³C-labeling in the fructosyl and glucosyl moieties of sucrose directly informs about the labeling of cytosolic F6P and G6P, respectively. To date, the most commonly used method to monitor sucrose labeling is by nuclear magnetic resonance, which requires substantial amounts of biological sample. This study describes a new methodology that accurately measures the labeling in free sugars using liquid chromatography tandem mass spectrometry (LC-MS/MS). For this purpose, maize embryos were pulsed with [U-¹³C]-fructose, intracellular sugars were extracted, and their time-course labeling was analyzed by LC-MS/MS. Additionally, extracts were enzymatically treated with hexokinase to remove the soluble hexoses, and then invertase to cleave sucrose into fructose and glucose. Finally, the labeling in the glucosyl and fructosyl moieties of sucrose was determined by LC-MS/MS.

Immobilization of invertase in calcium alginate and calcium alginate-kappa-carrageenan beads and its application in bioethanol production

Invertase from Saccharomyces cerevisiae was entrapped in Ca-alginate and Ca-alginate-kappa-carrageenan matrix. Optimum pH for the free and immobilized invertase was found to be 4.5 and 5.5, respectively. The optimum hydrolysis temperature was 55 °C for both the free and immobilized forms. K_m values for free invertase and invertase entrapped in Ca-alginate and Ca-alginate-kappa-carrageenan beads were 15, 21, and 19 mM, respectively. Values of V_max for free invertase and invertase entrapped in Ca-alginate and Ca-alginate-kappa-carrageenan beads were 238, 186, and 197 mM min^-1, respectively. Invertase entrapped in Ca-alginate-kappa-carrageenan matrix had the highest pH and thermal stability, higher reusability with 71% retention in activity after nine batches of reuse and higher storage stability with 86% activity retention after 12 weeks at 4 °C, pH 4.5. Fermentation of cane molasses by yeast for bioethanol formation in the presence of free invertase at 30 °C, pH 5.0, led to an increase in ethanol production by 3%. However, the production increased by 9% when invertase entrapped in Ca-alginate-kappa-carrageenan was used as a catalyst.HighlightsInvertase from Saccharomyces cerevisiae was entrapped in Ca-alginate beads.For efficient encapsulation of invertase, kappa-carrageenan was used in combination with alginate as a matrix.Entrapment in Ca-alginate-kappa-carrageenan increased pH and thermal stability of invertase.Invertase entrapped in Ca-alginate-kappa-carrageenan was used for bioethanol production from cane molasses.

The Effect of Diet on the Composition and Stability of Proteins Secreted by Honey Bees in Honey

Honey proteins are essential bee nutrients and antimicrobials that protect honey from microbial spoilage. The majority of the honey proteome includes bee-secreted peptides and proteins, produced in specialised glands; however, bees need to forage actively for nitrogen sources and other basic elements of protein synthesis. Nectar and pollen of different origins can vary significantly in their nutritional composition and other compounds such as plant secondary metabolites. Worker bees producing and ripening honey from nectar might therefore need to adjust protein secretions depending on the quality and specific contents of the starting material. Here, we assessed the impact of different food sources (sugar solutions with different additives) on honey proteome composition and stability, using controlled cage experiments. Honey-like products generated from sugar solution with or without additional protein, or plant secondary metabolites, differed neither in protein quality nor in protein quantity among samples. Storage for 4 weeks prevented protein degradation in most cases, without differences between food sources. The honey-like product proteome included several major royal jelly proteins, alpha-glucosidase and glucose oxidase. As none of the feeding regimes resulted in different protein profiles, we can conclude that worker bees may secrete a constant amount of each bee-specific protein into honey to preserve this highly valuable hive product.

Production of inulin- and neolevan-type fructooligosaccharides by Penicillium janczewskii Zaleski CCIBt 3352

Fructooligosaccharides (FOS) are fructose-based oligosaccharides employed as additives to improve the nutritional and technological properties of foods. The rhizosphere of inulin-accumulating plants from the Cerrado (Brazilian savanna) harbor fungi capable of synthesizing FOS from sucrose through the transfructosylating activity of β-fructosyltransferases and/or β-fructofuranosidases. Here, we investigated the ability of Penicillium janczewskii Zaleski CCIBt 3352, a fungus isolated from the rhizosphere of Chrysolaena obovata (Asteraceae), to produce FOS in a medium supplemented with sucrose concentrations of 30, 100, or 150 g L^-1 . Hydrolytic activity on sucrose was observed in culture filtrates; however, at 150 g L^-1 sucrose, the accumulation of 8 g L^-1 1-kestose (inulin-type FOS) and 7.3 g L^-1 neokestose (neolevan-type FOS) was observed, the latter being a type of FOS not commonly produced by filamentous fungi. In addition, minor amounts of four unidentified oligosaccharides, with a high degree of polymerization, were detected. The production of FOS was also observed in enzymatic assays, indicating the presence of extracellular enzymes with transfructosylating activity in the culture filtrates. Our findings demonstrate the feasibility of isolating promising microorganisms, for the production of FOS-synthesizing enzymes, from the rhizosphere of fructan-producing plants of the Brazilian Cerrado.

VvSWEET10 Mediates Sugar Accumulation in Grapes

Sugar accumulation is a critical event during grape berry ripening that determines the grape market values. Berry cells are highly dependent on sugar transporters to mediate cross-membrane transport. However, the role of sugar transporters in improving sugar accumulation in berries is not well established in grapes. Herein we report that a Sugars Will Eventually be Exported Transporter (SWEET), that is, VvSWEET10, was strongly expressed at the onset of ripening (véraison) and can improve grape sugar content. VvSWEET10 encodes a plasma membrane-localized transporter, and the heterologous expression of VvSWEET10 indicates that VvSWEET10 is a hexose-affinity transporter and has a broad spectrum of sugar transport functions. VvSWEET10 overexpression in grapevine calli and tomatoes increased the glucose, fructose, and total sugar levels significantly. The RNA sequencing results of grapevine transgenic calli showed that many sugar transporter genes and invertase genes were upregulated and suggest that VvSWEET10 may mediate sugar accumulation. These findings elucidated the role of VvSWEET10 in sugar accumulation and will be beneficial for the improvement of grape berry quality in the future.

Bioconversion of Beet Molasses to Alpha-Galactosidase and Ethanol

Molasses are sub-products of the sugar industry, rich in sucrose and containing other sugars like raffinose, glucose, and fructose. Alpha-galactosidases (EC. 3.2.1.22) catalyze the hydrolysis of alpha-(1,6) bonds of galactose residues in galacto-oligosaccharides (melibiose, raffinose, and stachyose) and complex galactomannans. Alpha-galactosidases have important applications, mainly in the food industry but also in the pharmaceutical and bioenergy sectors. However, the cost of the enzyme limits the profitability of most of these applications. The use of cheap sub-products, such as molasses, as substrates for production of alpha-galactosidases, reduces the cost of the enzymes and contributes to the circular economy. Alpha-galactosidase is a specially indicated bioproduct since, at the same time, it allows to use the raffinose present in molasses. This work describes the development of a two-step system for the valuation of beet molasses, based on their use as substrate for alpha-galactosidase and bioethanol production by Saccharomyces cerevisiae. Since this yeast secretes high amounts of invertase, to avoid congest the secretory route and to facilitate alpha-galactosidase purification from the culture medium, a mutant in the SUC2 gene (encoding invertase) was constructed. After a statistical optimization of culture conditions, this mutant yielded a very high rate of molasses bioconversion to alpha-galactosidase. In the second step, the SUC2 wild type yeast strain fermented the remaining sucrose to ethanol. A procedure to recycle the yeast biomass, by using it as nitrogen source to supplement molasses, was also developed.

Cellulase Production of Trichoderma reesei (Hypocrea jecorina) by Continuously Fed Cultivation Using Sucrose as Primary Carbon Source

To expand the range of soluble carbon sources for our enzyme production system, we investigated the properties of sucrose utilization and its effect on cellulase production by Trichoderma reesei M2-1. We performed batch cultivation of T. reesei M2-1 on sucrose and related sugars along with cellobiose, which was used as a cellulase inducer. The results clearly revealed that the hydrolysis products of sucrose, i.e. glucose and fructose, but not sucrose, can be used as a carbon source for enzyme production. In a 10-day continuous feeding experiment using invertase-treated sucrose/cellobiose, the fungal strain produced cellulases with a filter paper-degrading activity of 20.3 U/mL and production efficiency of 254 U/g-carbon sources. These values were comparable with those of glucose/cellobiose feeding (21.2 U/mL and 265 U/g-carbon sources, respectively). Furthermore, the comparison of the specific activities clearly indicated that the compositions of both produced enzymes were similar. Therefore, enzymatically hydrolyzed sucrose can be utilized as an alternative carbon source to glucose in our enzyme production system with T. reesei M2-1.

Factorial and Economic Evaluation of an Aqueous Two-Phase Partitioning Pilot Plant for Invertase Recovery From Spent Brewery Yeast

Aqueous two-phase systems (ATPS) have been reported as an attractive biocompatible extraction system for recovery and purification of biological products. In this work, the implementation, characterization, and optimization (operational and economic) of invertase extraction from spent brewery yeast in a semi-automatized pilot plant using ATPS is reported. Gentian violet was used as tracer for the selection of phase composition through phase entrainment minimization. Yeast suspension was chosen as a complex cell matrix model for the recovery of the industrial relevant enzyme invertase. Flow rates of phases did not have an effect, given that a bottom continuous phase is given, while load of sample and number of agitators improved the recovery of the enzyme. The best combination of factors reached a recovery of 129.35 ± 2.76% and a purification factor of 4.98 ± 1.10 in the bottom phase of a PEG-Phosphate system, also resulting in the removal of inhibitor molecules increasing invertase activity as reported by several other authors. Then, an economic analysis was performed to study the production cost of invertase analyzing only the significant parameters for production. Results indicate that the parameters being analyzed only affect the production cost per enzymatic unit, while variations in the cost per batch are not significant. Moreover, only the sample load is significant, which, combined with operational optimization results, gives the same optimal result for operation, maximizing recovery yield (15% of sample load and 1 static mixer). Overall res ults of these case studies show continuous pilot-scale ATPS as a viable and reproducible extraction/purification system for high added-value biological compounds.