Fructan 1-exohydrolase is associated with flower opening in Campanula rapunculoides

Exploring Metabolic Pathways and Gene Mining During Cotton Flower Bud Differentiation Stages Based on Transcriptomics and Metabolomics

Cotton is regarded as one of the significant economic crops in China, and its earliness is defined as one of the crucial traits influencing fiber quality and yield. To study the physiological and biochemical mechanisms related to early-maturing traits of cotton, cotton shoot apexes at the one-leaf, three-leaf, and five-leaf stages of the early-maturing cotton CCRI50 and late-maturing cotton Guoxinmian11 were collected for transcriptome sequencing and metabolomics, respectively. A total of 616, 782, and 842 differentially expressed genes (DEGs) at the one-leaf stage, three-leaf stage, and five-leaf stage were obtained through transcriptome sequencing, respectively. The metabolic detection results showed that 68, 56, and 62 differential metabolites (DMs) were obtained in the three periods, respectively. A total of 10 DMs were detected simultaneously from the one-leaf to five-leaf stage, 4 of which were phenolic acids and down-regulated in the early maturing variety CCRI50. A combined transcriptomic and metabolomic analysis revealed that phenylpropanoid biosynthesis, tyrosine metabolism, and phenylalanine metabolism might be important metabolic pathways in cotton bud differentiation. GhTYDC-A01 was identified in both the tyrosine metabolism and phenylalanine metabolism pathways, and it was highly expressed in pistils. To investigate the function of this gene in flowering, we overexpressed it in Arabidopsis thaliana. Compared to the wild type, the flowering time of the overexpression of GhTYDC-A01 in Arabidopsis was delayed. This study provides valuable resources and new insights into the relationship between metabolites and early-maturing cotton.

Insights into the convergent evolution of fructan biosynthesis in angiosperms from the highly characteristic chicory genome

Fructans in angiosperms play essential roles in physiological functions and environmental adaptations. As a major source of industrial fructans (especially inulin-type), chicory (Cichorium intybus L.) is a model species for studying fructan biosynthesis. However, the genes underlying this process and their evolutionary history in angiosperms remain elusive. We combined multiple sequencing technologies to assemble and annotate the chicory genome and scan its (epi)genomic features, such as genomic components, DNA methylation, and three-dimensional (3D) structure. We also performed a comparative genomics analysis to uncover the associations between key traits and gene families. We achieved a nearly complete chicory genome assembly and found that continuous bursts of a few highly active retrotransposon families largely shaped the (epi)genomic characteristics. The highly methylated genome with its unique 3D structure potentially influences critical biological processes. Our comprehensive comparative genomics analysis deciphered the genetic basis for the rich sesquiterpene content in chicory and indicated that the fructan-accumulating trait resulted from convergent evolution in angiosperms due to shifts in critical sites of fructan-active enzymes. The highly characterized chicory genome provides insight into Asteraceae evolution and fructan biosynthesis in angiosperms.

Role of metabolites in flower development and discovery of compounds controlling flowering time

Flowering is one of the most important physiological processes of plants that ensures continuity of genetic flow from one generation to the next and also maintains food security. Therefore, impact of various climate-related abiotic stresses on flowering have been assessed to evaluate the long-term impact of global climate change. In contrast to the enormous volume of research that has been conducted at the genetic, transcriptional, post-transcriptional, and protein level, much less attention has been paid to understand the role of various metabolites in flower induction and floral organ development during normal growth or in stressed environmental condition. This review article aims at summarizing information on various primary (e.g., carbohydrates, lipids, fatty acid derivatives, protein and amino acids) and secondary metabolites (e.g., polyamines, phenolics, neuro-indoles, phenylpropanoid, flavonoids and terpenes) that have so far been identified either during flower induction or in individual floral organs implying their possible role in organ development. Specialized metabolites responsible for flower colour, scent and shape to support plant-pollinator interaction have been extensively reviewed by many research groups and hence are not considered in this article. Many of the metabolites discussed here may be used as metabolomarkers to identify tolerant crop genotypes. Several agrochemicals have been successfully used to release endodormancy in temperate trees. Along the same line, a strategy that combines metabolite profiling, screening of small-molecule libraries, and structural alteration of selected compounds has been proposed in order to identify novel lead compounds that can regulate flowering time when applied exogenously.

Production of fructan synthesis/hydrolysis of endophytic bacteria involved in inulin production in Jerusalem artichoke

Endophytic bacteria refer to bacteria which promote plant growth via direct and indirect mechanisms. Three endophytic bacteria isolated from Jerusalem artichoke exhibited plant growth induction and inulin production. These bacteria had functions of fructan degradation and synthesis from inulinase and levansucrase, respectively. Rossellomorea aquimaris 3.13 and Priestia megaterium 3.5 obtained inulinase/levanase enzyme with inulin and levan as substrates; enzyme production showed the optimum conditions in 1% inulin medium of 35 °C, pH 7.0. Bacillus velezensis 5.18 and Priestia megaterium 3.5 had inulosucrase/levansucrase enzyme with sucrose as a major carbon source; the enzyme had optimum temperature and pH conditions of 30 °C and pH 7.0, respectively. A combination of carbon sources had effect on decreasing enzyme activity; in addition, co-inoculation of bacteria showed a slight difference in enzyme production compared with single inoculation. The inulosucrase/levansucrase was produced earlier in co-culture containing bacteria with inulinase activity. Plant fructan synthesis was involved in 1-SST and 1-FFT, while 1-FEH encoded inulin degradation; these genes were evaluated in Jerusalem artichoke inoculated with the endophytic bacteria to quantify gene expression level using qPCR. All genes expressed in low levels at early stage of growth, responding to all endophytic bacteria. Significantly, Bacillus velezensis 5.18 induced all genes of the plant at 65 days of inoculation; Rossellomorea aquimaris 3.13 induced 1-FFT while Priestia megaterium 3.5 induced 1-SST.

Drone phenotyping and machine learning enable discovery of loci regulating daily floral opening in lettuce

Flower opening and closure are traits of reproductive importance in all angiosperms because they determine the success of self- and cross-pollination. The temporal nature of this phenotype rendered it a difficult target for genetic studies. Cultivated and wild lettuce, Lactuca spp., have composite inflorescences that open only once. An L. serriola×L. sativa F6 recombinant inbred line (RIL) population differed markedly for daily floral opening time. This population was used to map the genetic determinants of this trait; the floral opening time of 236 RILs was scored using time-course image series obtained by drone-based phenotyping on two occasions. Floral pixels were identified from the images using a support vector machine with an accuracy >99%. A Bayesian inference method was developed to extract the peak floral opening time for individual genotypes from the time-stamped image data. Two independent quantitative trait loci (QTLs; Daily Floral Opening 2.1 and qDFO8.1) explaining >30% of the phenotypic variation in floral opening time were discovered. Candidate genes with non-synonymous polymorphisms in coding sequences were identified within the QTLs. This study demonstrates the power of combining remote sensing, machine learning, Bayesian statistics, and genome-wide marker data for studying the genetics of recalcitrant phenotypes.

Comparison of carbohydrate partitioning and expression patterns of some genes involved in carbohydrate biosynthesis pathways in annual and biennial species of Cichorium spp

Variation in metabolism and partitioning of carbohydrates, particularly fructans, between annual and perennial Cichorium species remains a challenging topic. To address this problem, an annual (endive, Cichorium endive L. var. Crispum; Asteraceae) and a biennial species (chicory, Cichorium intybus L. var. Witloof; Asteraceae) were compared with in terms of variability in carbohydrate accumulation and expression patterns of fructan-active enzyme genes, as well as sucrose metabolism at various growth and developmental stages. In general, constituents such as 1-kestose, nystose, and inulin were detected only in the root of chicory and were not present in any of the endive tissues. For both species, flower tissue contained maximum levels of both fructose and glucose, while for sucrose, more fluctuations were observed. On the other hand, all the genes under study exhibited variation, not only between the two species but also among different tissues at different sampling times. In endive root compared to endive leaf, the expression of cell wall invertase genes and sucrose accumulation decreased simultaneously, indicating the limited capacity of its roots to absorb sucrose, a precursor to inulin production. In addition, low expression of fructan: fructan fructosyltransferase in endive root compared to chicory root confirmed the inability of endive to inulin synthesis. Overall, annual and biennial species were different in the production of inulin, transport, remobilization, and unloading of sucrose.

Cloning and functional characterization of two abiotic stress-responsive Jerusalem artichoke (Helianthus tuberosus) fructan 1-exohydrolases (1-FEHs)

Two fructan hydrolases were previously reported to exist in Jerusalem artichoke (Helianthus tuberosus) and one native fructan-β-fructosidase (1-FEH) was purified to homogeneity by SDS-PAGE, but no corresponding cDNA was cloned. Here, we cloned two full-length 1-FEH cDNA sequences from Jerusalem artichoke, named Ht1-FEH I and Ht1-FEH II, which showed high levels of identity with chicory 1-FEH I and 1-FEH II. Functional characterization of the corresponding recombinant proteins in Pichia pastoris X-33 demonstrated that both Ht1-FEHs had high levels of hydrolase activity towards β(2,1)-linked fructans, but low or no activity towards β(2,6)-linked levan and sucrose. Like other plant FEHs, the activities of the recombinant Ht1-FEHs were greatly inhibited by sucrose. Real-time quantitative PCR analysis showed that Ht1-FEH I transcripts accumulated to high levels in the developing leaves and stems of artichoke, whereas the expression levels of Ht1-FEH II increased in tubers during tuber sprouting, which implies that the two Ht1-FEHs play different roles. The levels of both Ht1-FEH I and II transcript were significantly increased in the stems of NaCl-treated plants. NaCl treatment also induced transcription of both Ht1-FEHs in the tubers, while PEG treatments slightly inhibited the expression of Ht1-FEH II in tubers. Analysis of sugar-metabolizing enzyme activities and carbohydrate concentration via HPLC showed that the enzyme activities of 1-FEHs were increased but the fructose content was decreased under NaCl and PEG treatments. Given that FEH hydrolyzes fructan to yield Fru, we discuss possible explanations for the inconsistency between 1-FEH activity and fructan dynamics in artichokes subjected to abiotic stress.

Photoperiodic variations induce shifts in the leaf metabolic profile of Chrysanthemum morifolium

Plants have a high ability to adjust their metabolism, growth and development to changes in the light environment and to photoperiodic variation, but the current knowledge on how changes in metabolite contents are associated with growth and development is limited. We investigated the effect of three different photoperiodic treatments with similar daily light integral (DLI) on the growth responses and diurnal patterns in detected leaf metabolites in the short day plant Chrysanthemum×morifolium Ramat. Treatments were long day (LD, 18h light/6h dark), short day (SD, 12h light/12h dark) and short day with irregular night interruptions (NI-SD,12h light/12h dark, applied in a weekly pattern, shifting from day-to-day). Photoperiodic variation resulted in changes in the phenotypic development of the plants. The plants grown in the SD treatment started to initiate reproductive development of the meristems and a decrease in leaf expansion resulted in lower leaf area of expanding leaves. In contrast, plants in the NI-SD and LD treatments did not show reproductive development at any stage and final leaf area of the expanding leaves was intermediate for the NI-SD plants and largest for the LD plants. Photoperiodic variation also resulted in changes in the leaf metabolic profile for most of the analysed metabolites, but only carbohydrates, citrate and some amino acids displayed a shift in their diurnal pattern. Further, our results illustrated that short days (SD) increased the diurnal turnover of 1-kestose after 2 weeks, and decreased the overall contents of leaf hexoses after 3 weeks. In the two other treatments a diurnal turnover of 1-kestose was not stimulated before after 3 weeks, and hexoses together with the hexose:sucrose ratio steadily increased during the experiment. Our results enlighten the plasticity of leaf growth and metabolism to environmental changes, and demonstrate that diurnally regulated metabolites not always respond to photoperiodic variation.

Manninotriose is a major carbohydrate in red deadnettle (Lamium purpureum, Lamiaceae)

BACKGROUND AND AIMS

There is a great need to search for natural compounds with superior prebiotic, antioxidant and immunostimulatory properties for use in (food) applications. Raffinose family oligosaccharides (RFOs) show such properties. Moreover, they contribute to stress tolerance in plants, acting as putative membrane stabilizers, antioxidants and signalling agents.

METHODS

A large-scale soluble carbohydrate screening was performed within the plant kingdom. An unknown compound accumulated to a high extent in early-spring red deadnettle (Lamium purpureum) but not in other RFO plants. The compound was purified and its structure was unravelled with NMR. Organs and organ parts of red deadnettle were carefully dissected and analysed for soluble sugars. Phloem sap content was analysed by a common EDTA-based method.

KEY RESULTS

Early-spring red deadnettle stems and roots accumulate high concentrations of the reducing trisaccharide manninotriose (Galα1,6Galα1,6Glc), a derivative of the non-reducing RFO stachyose (Galα1,6Galα1,6Glcα1,2βFru). Detailed soluble carbohydrate analyses on dissected stem and leaf sections, together with phloem sap analyses, strongly suggest that stachyose is the main transport compound, but extensive hydrolysis of stachyose to manninotriose seems to occur along the transport path. Based on the specificities of the observed carbohydrate dynamics, the putative physiological roles of manninotriose in red deadnettle are discussed.

CONCLUSIONS

It is demonstrated for the first time that manninotriose is a novel and important player in the RFO metabolism of red dead deadnettle. It is proposed that manninotriose represents a temporary storage carbohydrate in early-spring deadnettle, at the same time perhaps functioning as a membrane protector and/or as an antioxidant in the vicinity of membranes, as recently suggested for other RFOs and fructans. This novel finding urges further research on this peculiar carbohydrate on a broader array of RFO accumulators.

TaMYB13 is a transcriptional activator of fructosyltransferase genes involved in β-2,6-linked fructan synthesis in wheat

Fructans are soluble fructosyl-oligosaccharides deposited in many cool-season grass species as a carbon reserve; they are synthesised by fructosyltransferases. In wheat and barley fructans can accumulate in mature stems at a very high level and serve as an important carbon source for grain filling. Fructan synthesis in temperate cereals is regulated by sucrose level and developmental signals, and functions as a metabolic adjustment for carbon balance between carbon supply and sink demand. In this study the expression levels of a highly homologous group of Triticum aestivumMYB genes (TaMYB13-1, TaMYB13-2 and TaMYB13-3) were found to be positively correlated with the mRNA levels of sucrose:sucrose 1-fructosyltransferase (1-SST) and sucrose:fructan 6-fructosyltransferase (6-SFT) in wheat stems among recombinant inbred lines with a wide range of fructan concentrations through Affymetrix array expression analysis. This expression correction extended to expression profiles during stem development. TaMYB13 contains an R2R3-type MYB domain. In vitro random DNA-binding site selection followed by base substitution mutagenesis revealed that TaMYB13 bound to a (A/G/T)TT(A/T/C)GGT core sequence, which was present in the promoters of wheat Ta1-SST and Ta6-SFT genes as well as a barley Hv6-SFT gene. Transactivation analysis showed that TaMYB13 was a transcriptional activator and could markedly enhance the expression of 1-SST and 6-SFT promoter-driven reporter genes in wheat. Elimination of TaMYB13-binding sites in Ta6-SFT and Ta1-SST promoters markedly reduced TaMYB13-mediated reporter gene transactivation. These data suggest that TaMYB13 and its orthologues are positive regulators for controlling the expression of major fructosyltransferases involved in the fructan synthetic pathway in temperate cereals.

Cloning and functional characterization of a fructan 1-exohydrolase (1-FEH) in the cold tolerant Patagonian species Bromus pictus

Fructans are fructose polymers synthesized in a wide range of species such as bacteria, fungi and plants. Fructans are synthesized by fructosyltransferases (FTs) and depolymerized by fructan exohydrolases (FEHs). Bromus pictus is a graminean decaploid species from the Patagonian region of Argentina, which accumulates large amounts of fructans even at temperate temperatures. The first gene isolated from B. pictus fructan metabolism was a putative sucrose:fructan 6-fructosyltransferase (6-SFT). Here, a complete cDNA of the first fructan exohydrolase (FEH) from B. pictus (Bp1-FEHa) was isolated using RT-PCR strategies. The Bp1-FEHa encoding gene is present as a single copy in B. pictus genome. Functional characterization in Pichia pastoris confirmed Bp1-FEHa is a fructan exohydrolase with predominant activity towards beta-(2-1) linkages. Its expression was analyzed in different leaf sections, showing the highest expression levels in the second section of the sheath and the tip of the blade. Bp1-FEHa expression was studied along with FEH and FT activities and fructan accumulation profile in response to chilling conditions during a 7-day time course experiment. Bp1-FEHa expression and FEH activity followed a similar pattern in response to low temperatures, especially in basal sections of the sheaths. In these sections the FEH and FT activities were particularly high and they were significantly correlated to fructan accumulation profile, along with cold treatment.

Sucrose, sucrosyl oligosaccharides, and oxidative stress: scavenging and salvaging?

In nature, no single plant completes its life cycle without encountering environmental stress. When plant cells surpass stress threshold stimuli, chemically reactive oxygen species (ROS) are generated that can cause oxidative damage or act as signals. Plants have developed numerous ROS-scavenging systems to minimize the cytotoxic effects of ROS. The role of sucrosyl oligosaccharides (SOS), including fructans and the raffinose family oligosaccharides (RFOs), is well established during stress physiology. They are believed to act as important membrane protectors in planta. So far a putative role for sucrose and SOS during oxidative stress has largely been neglected, as has the contribution of the vacuolar compartment. Recent studies suggest a link between SOS and oxidative defence and/or scavenging. SOS might be involved in stabilizing membrane-associated peroxidases and NADPH oxidases, and SOS-derived radicals might fulfil an intermediate role in oxido-reduction reactions taking place in the vicinity of membranes. Here, these emerging features are discussed and perspectives for future research are provided.

Cloning, characterization and functional analysis of a 1-FEH cDNA from Vernonia herbacea (Vell.) Rusby

Variations in the inulin contents have been detected in rhizophores of Vernonia herbacea during the phenological cycle. These variations indicate the occurrence of active inulin synthesis and depolymerization throughout the cycle and a role for this carbohydrate as a reserve compound. 1-Fructan exohydrolase (1-FEH) is the enzyme responsible for inulin depolymerization, and its activity has been detected in rhizophores of sprouting plants. Defoliation and low temperature are enhancer conditions of this 1-FEH activity. The aim of the present work was the cloning of this enzyme. Rhizophores were collected from plants induced to sprout, followed by storage at 5 degrees C. A full length 1-FEH cDNA sequence was obtained by PCR and inverse PCR techniques, and expressed in Pichia pastoris. Cold storage enhances FEH gene expression. Vh1-FEH was shown to be a functional 1-FEH, hydrolyzing predominantly beta-2,1 linkages, sharing high identity with chicory FEH sequences, and its activity was inhibited by 81% in the presence of 10 mM sucrose. In V. herbacea, low temperature and sucrose play a role in the control of fructan degradation. This is the first study concerning the cloning and functional analysis of a 1-FEH cDNA of a native species from the Brazilian Cerrado. Results will contribute to understanding the role of fructans in the establishment of a very successful fructan flora of the Brazilian Cerrado, subjected to water limitation and low temperature during winter.

Freezing tolerance by vesicle-mediated fructan transport

Fructans are fructose-based polymers associated with freezing tolerance. They might act directly via membrane stabilization or indirectly by stimulating alternative cryoprotectants. Fructans and fructan biosynthetic enzymes, in general, are believed to be present in the vacuole. This paper draws particular attention to the surprising presence of fructans and fructan exohydrolase activity in the apoplast of cold-stressed plants. This observation raises questions concerning the origin of apoplastic fructans and suggests that fructans are transported to the apoplast by post-synthesis mechanisms, perhaps induced by cold. We propose a conceptual vesicle-mediated transport model for the movement of vacuolar fructans to the apoplast, where they could assist in stabilizing the plasma membrane.

Plant fructans in stress environments: emerging concepts and future prospects

Plants are sessile and sensitive organisms known to possess various regulatory mechanisms for defending themselves under stress environments. Fructans are fructose-based polymers synthesized from sucrose by fructosyltransferases (FTs). They have been increasingly recognized as protective agents against abiotic stresses. Using model membranes, numerous in vitro studies have demonstrated that fructans can stabilize membranes by direct H-bonding to the phosphate and choline groups of membrane lipids, resulting in a reduced water outflow from the dry membranes. Inulin-type fructans are flexible random-coiled structures that can adopt many conformations, allowing them to insert deeply within the membranes. The devitrification temperature (T(g)) can be adjusted by their varying molecular weights. In addition, above T(g) their low crystallization rates ensure prolonged membrane protection. Supporting, in vivo studies with transgenic plants expressing FTs showed fructan accumulation and an associated improvement in freezing and/or chilling tolerance. The water-soluble nature of fructans may allow their rapid adaptation as cryoprotectants in order to give optimal membrane protection. One of the emerging concepts for delivering vacuolar fructans to the extracellular space for protecting the plasma membrane is vesicle-mediated, tonoplast-derived exocytosis. It should, however, be noted that natural stress tolerance is a very complex process that cannot be explained by the action of a single molecule or mechanism.