Transgene silencing of sucrose synthase in alfalfa (Medicago sativa L.) stem vascular tissue suggests a role for invertase in cell wall cellulose synthesis

Exploring the role of GhN/AINV23: implications for plant growth, development, and drought tolerance

BACKGROUND

Neutral/alkaline invertases (N/AINVs) play a crucial role in plant growth, development, and stress response, by irreversibly hydrolyzing sucrose into glucose and fructose. However, research on cotton in this area is limited. This study aims to investigate GhN/AINV23, a neutral/alkaline invertase in cotton, including its characteristics and biological functions.

RESULTS

In our study, we analyzed the sequence information, three-dimensional (3D) model, phylogenetic tree, and cis-elements of GhN/AINV23. The localization of GhN/AINV23 was determined to be in the cytoplasm and cell membrane. Quantitative real-time polymerase chain reaction (qRT-PCR) results showed that GhN/AINV23 expression was induced by abscisic acid (ABA), exogenous sucrose and low exogenous glucose, and inhibited by high exogenous glucose. In Arabidopsis, overexpression of GhN/AINV23 promoted vegetative phase change, root development, and drought tolerance. Additionally, the virus-induced gene silencing (VIGS) assay indicated that the inhibition of GhN/AINV23 expression made cotton more susceptible to drought stress, suggesting that GhN/AINV23 positively regulates plant drought tolerance.

CONCLUSION

Our research indicates that GhN/AINV23 plays a significant role in plant vegetative phase change, root development, and drought response. These findings provide a valuable foundation for utilizing GhN/AINV23 to improve cotton yield.

Critical metabolic pathways and SAD/FADs, WRI1s, and DGATs cooperate for high-oleic acid oil production in developing oil tea (Camellia oleifera) seeds

Oil tea trees produce high-quality edible oils with desirably high oleic acid (18:1) and low linoleic (18:2) and linolenic (18:3) fatty acid (FA) levels, but limited understanding of tea oil biosynthesis and regulation has become a significant obstacle for the breeding of high-yield and -quality oil tea varieties. By integrating metabolite and transcriptome analyses of developing oil tea seeds, we dissected the critical metabolic pathways, including glycolysis, fatty acid, and triacylglycerol (TAG) biosynthesis, as well as genes essential for tea seed oil production. Two plastidic stearoyl-acyl carrier protein desaturases (CoSAD1 and 2) and two endoplasmic reticulum-localized FA desaturases (CoFAD2 and 3) were functionally characterized as responsible for high 18:1 and low 18:2 and 18:3 proportions in tea oils. Two diacylglycerol O-acyltransferases (CoDGAT1 and 2) that may prefer to synthesize 18:1-TAG were functionally characterized and might be also important for high 18:1-TAG production. The highly expressed CoWRI1a and b were identified and characterized as activators of glycolysis and regulators of directing source carbon flux into FA biosynthesis in developing oil tea seeds. The upregulated CoSADs with downregulated CoFAD2 and CoFAD3 at the late seed developmental stages mainly accounted for high 18:1 levels. Two CoDGATs might be responsible for assembling TAGs with oleoyl acyl chains, whilst two CoWRI1s regulated carbons from parental sources, partitioning into oil production in oil tea embryo sinks. This study provides a deep understanding of the biosynthesis of tea seed oils and information on genes that may be used as molecular markers to breed oil tea varieties with higher oil yield and quality.

Restriction of cytosolic sucrose hydrolysis profoundly alters development, metabolism, and gene expression in Arabidopsis roots

Plant roots depend on sucrose imported from leaves as the substrate for metabolism and growth. Sucrose and hexoses derived from it are also signalling molecules that modulate growth and development, but the importance for signalling of endogenous changes in sugar levels is poorly understood. We report that reduced activity of cytosolic invertase, which converts sucrose to hexoses, leads to pronounced metabolic, growth, and developmental defects in roots of Arabidopsis (Arabidopsis thaliana) seedlings. In addition to altered sugar and downstream metabolite levels, roots of cinv1 cinv2 mutants have reduced elongation rates, cell and meristem size, abnormal meristematic cell division patterns, and altered expression of thousands of genes of diverse functions. Provision of exogenous glucose to mutant roots repairs relatively few of the defects. The extensive transcriptional differences between mutant and wild-type roots have hallmarks of both high sucrose and low hexose signalling. We conclude that the mutant phenotype reflects both low carbon availability for metabolism and growth and complex sugar signals derived from elevated sucrose and depressed hexose levels in the cytosol of mutant roots. Such reciprocal changes in endogenous sucrose and hexose levels potentially provide rich information about sugar status that translates into flexible adjustments of growth and development.

GhN/AINV13 positively regulates cotton stress tolerance by interacting with the 14-3-3 protein

Neutral/alkaline invertases (N/AINVs) are sucrose hydrolases with important roles in plants. In this study, 15, 15, 15, 29, and 30 N/AINVs were identified in the Gossypium species, G. raimondii, G. herbaceum, G. arboreum, G. hirsutum, and G. barbadense, respectively. Along with two previously discovered branches, α and β, a new clade γ was first discovered in our study. Investigation of gene collinearity showed that whole-genome duplication (WGD) and polyploidization were responsible for the expansion of the N/AINV gene family in allopolyploid Gossypium. Moreover, expression patterns revealed that GhN/AINV3/13/17/23/24/28 from the β clade is highly expressed during the period of fiber initiation. The invertase activity of GhN/AINV13 and GhN/AINV23 were confirmed by restoring defects of invertase-deficient yeast mutant SEY2102. Treatments of abiotic stress showed that most GhN/AINVs were induced in response to polyethylene glycol (PEG) or salt stress. A virus-induced gene-silencing (VIGS) experiment and yeast two-hybrid assay demonstrated that GhN/AINV13 may interact with their positive regulators Gh14-3-3 proteins and participate in the fiber initiation or stress tolerance of cotton. Our results provided fundamental information regarding N/AINVs and highlight their potential functions in cotton stress tolerance.

Life Cycle Assessment Analysis of Alfalfa and Corn for Biogas Production in a Farm Case Study

In the last years the greenhouse effect has been significantly intensified due to human activities, generating large additional amounts of Greenhouse gases (GHG). The fossil fuels are the main causes of that. Consequently, the attention on the composition of the national fuel mix has significantly grown, and the renewables are becoming a more significant component. In this context, biomass is one of the most important sources of renewable energy with a great potential for the production of energy. The study has evaluated, through an LCA (Life Cycle Assessment) study, the attitude of alfalfa (Medicago sativa) as “no food” biomass alternative to maize silage (corn), in the production of biogas from anaerobic digestion. Considering the same functional unit (1 m3 of biogas from anaerobic digestion) and the same time horizon, alfalfa environmental impact was found to be much comparable to that of corn because it has an impact of about 15% higher than corn considering the total score from different categories and an impact of 5% higher of corn considering only greenhouse gases. Therefore, the analysis shows a similar environmental load in the use of alfalfa biomass in energy production compared to maize. Corn in fact, despite a better yield per hectare and yield of biogas, requires a greater amount of energy inputs to produce 1m3 of biogas, while alfalfa, which requires less energy inputs in its life cycle, has a lower performance in terms of yield. The results show the possibility to alternate the two crops for energy production from an environmental perspective.

Transcriptional analysis reveals sodium nitroprusside affects alfalfa in response to PEG-induced osmotic stress at germination stage

Drought is one of the most common environmental factors that affect alfalfa germination and development. Nitric oxide (NO) could mediate stress tolerance in plants. The goal of this study was to determine exogenous NO donor-mediated drought adaption molecular mechanisms during the alfalfa germination stage. In this study, physiological and transcriptome analyses were performed on 7 days of the growth period seedlings by sodium nitroprusside (SNP) and polyethylene glycol (PEG) treatment. The results showed that SNP supplementation alleviated malondialdehyde accumulation, increased levels of proline and soluble sugars, and enhanced antioxidant enzyme activity under osmotic stress conditions. RNA-Seq experiments identified 5828 genes exhibiting differential expression in seedlings treated with PEG, SNP, or SNP+PEG relative to seedlings treated with distilled water. Of these DEGs, 3235 were upregulated, and 2593 were downregulated relative to the controls. Fifteen DEGs were amplified by qRT-PCR to verify the changes in expression determined by RNA-Seq, revealing that PIF3, glnA, PLCG1, and RP-S11e exhibited enhanced expression under the SNP+PEG treatment. SNP was found to modulate redox homeostasis-related genes such as GSTs, SOD2, GPX, and RBOH, and triggered calcium signaling transduction. It also induced some key genes relating to the abscisic acid, ethylene, and auxin signaling transduction in response to PEG stress. Conversely, genes associated with secondary metabolite biosynthesis and the metabolism of starch and sucrose during osmotic stress were downregulated by SNP. These results provide new insights into SNP-mediated drought adaption mechanisms at transcriptome-wide in alfalfa and reveal key drought tolerance pathways in this species.

Transcriptional changes during tomato ripening and influence of brackish water irrigation on fruit transcriptome and sugar content

Efficient management and utilization of brackish water irrigation help to minimize yield losses and promote fruit quality and sugar content in tomato fruit. However, the functional genes involved in sugar metabolic pathways and potential molecular pathways responsive to brackish water irrigation remain unknown. To this end, physiological responses and comparative transcriptional profiling was used to analyze the tomato fruit during the white-ripe period (CK1) and mature period (CK2) in plants grown under four water management strategies (rotating irrigation with brackish and fresh water during fruit development, T1; fresh water irrigation, T2; mixed brackish and fresh water irrigation, T3; mixed water and fresh water irrigation in sequence, T4). Comparative analysis revealed that during fruit development (CK2 cv CK1) differentially expressed genes (DEGs) involved in photosynthetic pathways and sucrose-starch metabolism were downregulated. However, two DEGs encoding putative beta-fructofuranosidases were significantly upregulated at the mature stage, which promoted the accumulation of glucose and fructose in CK2. Comparing four types of management strategies, rotating irrigation with brackish water and fresh water (T1) led to reprograming of global gene expression. Moreover, the upregulated DEGs in T1 were significantly enriched for signaling, hormone metabolism, and stress tolerance, suggesting the coordination of both stresses signaling as well as the plant hormone. These results provide a valuable reference for rational use of brackish water in the production of high-quality tomato in arid and semi-arid regions.

Cytosolic invertases contribute to cellulose biosynthesis and influence carbon partitioning in seedlings of Arabidopsis thaliana

In plants, UDP-glucose is the direct precursor for cellulose biosynthesis, and can be converted into other NDP-sugars required for the biosynthesis of wall matrix polysaccharides. UDP-glucose is generated from sucrose by two distinct metabolic pathways. The first pathway is the direct conversion of sucrose to UDP-glucose and fructose by sucrose synthase. The second pathway involves sucrose hydrolysis by cytosolic invertase (CINV), conversion of glucose to glucose-6-phosphate and glucose-1-phosphate, and UDP-glucose generation by UDP-glucose pyrophosphorylase (UGP). Previously, Barratt et al. (Proc. Natl Acad. Sci. USA, 106, 2009 and 13124) have found that an Arabidopsis double mutant lacking CINV1 and CINV2 displayed drastically reduced growth. Whether this reduced growth is due to deficient cell wall production caused by limited UDP-glucose supply, pleiotropic effects, or both, remained unresolved. Here, we present results indicating that the CINV/UGP pathway contributes to anisotropic growth and cellulose biosynthesis in Arabidopsis. Biochemical and imaging data demonstrate that cinv1 cinv2 seedlings are deficient in UDP-glucose production, exhibit abnormal cellulose biosynthesis and microtubule properties, and have altered cellulose organization without substantial changes to matrix polysaccharide composition, suggesting that the CINV/UGP pathway is a key metabolic route to UDP-glucose synthesis in Arabidopsis. Furthermore, differential responses of cinv1 cinv2 seedlings to exogenous sugar supplementation support a function of CINVs in influencing carbon partitioning in Arabidopsis. From these data and those of previous studies, we conclude that CINVs serve central roles in cellulose biosynthesis and carbon allocation in Arabidopsis.

UDP-Sugar Producing Pyrophosphorylases: Distinct and Essential Enzymes With Overlapping Substrate Specificities, Providing de novo Precursors for Glycosylation Reactions

Nucleotide sugars are the key precursors for all glycosylation reactions and are required both for oligo- and polysaccharides synthesis and protein and lipid glycosylation. Among all nucleotide sugars, UDP-sugars are the most important precursors for biomass production in nature (e.g., synthesis of cellulose, hemicellulose, and pectins for cell wall production). Several recent studies have already suggested a potential role for UDP-Glc in plant growth and development, and UDP-Glc has also been suggested as a signaling molecule, in addition to its precursor function. In this review, we will cover primary mechanisms of formation of UDP-sugars, by focusing on UDP-sugar metabolizing pyrophosphorylases. The pyrophosphorylases can be divided into three families: UDP-Glc pyrophosphorylase (UGPase), UDP-sugar pyrophosphorylase (USPase), and UDP-N-acetyl glucosamine pyrophosphorylase (UAGPase), which can be distinguished both by their amino acid sequences and by differences in substrate specificity. Substrate specificities of these enzymes are discussed, along with structure-function relationships, based on their crystal structures and homology modeling. Earlier studies with transgenic plants have revealed that each of the pyrophosphorylases is essential for plant survival, and their loss or a decrease in activity results in reproductive impairment. This constitutes a problem when studying exact in vivo roles of the enzymes using classical reverse genetics approaches. Thus, strategies involving the use of specific inhibitors (reverse chemical genetics) are also discussed. Further characterization of the properties/roles of pyrophosphorylases should address fundamental questions dealing with mechanisms and control of carbohydrate synthesis and may allow to identify targets for manipulation of biomass production in plants.

Suppression of sucrose synthase affects auxin signaling and leaf morphology in tomato

Metabolic enzymes have been found to play roles in plant development. Sucrose synthase (SUS) is one of the two enzyme families involved in sucrose cleavage in plants. In tomato, six SUS genes have been found. We generated transgenic tomato plants with RNAi suppression of SlSUS1, SlSUS3 and SlSUS4 genes. Independent transgenic lines with RNAi suppression of more than one SUS gene exhibited morphological effects on their cotyledons and leaf structure, but there were no significant effects on their carbohydrate levels, demonstrating that SUS has a developmental function, in addition to its metabolic function. Shoot apices of the transgenic lines showed elevated expression of JAGGED (JAG) and the auxin transporter PIN1. In a PIN1-GFP fusion reporter/SUS-RNAi hybrid, PIN1-GFP patterns were altered in developing leaves (as compared to control plants), indicating that SlSUS suppression alters auxin signaling. These results suggest possible roles for SUS in the regulation of plant growth and leaf morphology, in association with the auxin-signaling pathway.

Cytosolic invertase contributes to the supply of substrate for cellulose biosynthesis in developing wood

Carbon for cellulose biosynthesis is derived from sucrose. Cellulose is synthesized from uridine 5'-diphosphoglucose (UDP-glucose), but the enzyme(s) responsible for the initial sucrose cleavage and the source of UDP-glucose for cellulose biosynthesis in developing wood have not been defined. We investigated the role of CYTOSOLIC INVERTASEs (CINs) during wood formation in hybrid aspen (Populus tremula × tremuloides) and characterized transgenic lines with reduced CIN activity during secondary cell wall biosynthesis. Suppression of CIN activity by 38-55% led to a 9-13% reduction in crystalline cellulose. The changes in cellulose were reflected in reduced diameter of acid-insoluble cellulose microfibrils and increased glucose release from wood upon enzymatic digestion of cellulose. Reduced CIN activity decreased the amount of the cellulose biosynthesis precursor UDP-glucose in developing wood, pointing to the likely cause of the cellulose phenotype. The findings suggest that CIN activity has an important role in the cellulose biosynthesis of trees, and indicate that cellulose biosynthesis in wood relies on a quantifiable UDP-glucose pool. The results also introduce a concept of altering cellulose microfibril properties by modifying substrate supply to cellulose biosynthesis.