Comparative Transcriptomics Suggests Early Modifications by Vintec® in Grapevine Trunk of Hormonal Signaling and Secondary Metabolism Biosynthesis in Response to Phaeomoniella chlamydospora and Phaeoacremonium minimum

Given their well-known antifungal abilities, species of the genus Trichoderma are of significant interest in modern agriculture. Recent studies have shown that Trichoderma species can induce plant resistance against different phytopathogens. To further extend this line of investigation, we investigate herein the transcriptomic response of grapevine trunk to Vintec^®, which is a Trichoderma atroviride SC1-based commercial formulation for biological control of grapevine trunk diseases and which reduces wood colonization. The aim of the study is to understand whether the biocontrol agent Vintec^® modifies the trunk response to Phaeoacremonium minimum and Phaeomoniella chlamydospora, which are two esca-associated fungal pathogens. An analysis of transcriptional regulation identifies clusters of co-regulated genes whose transcriptomic reprogramming in response to infection depends on the absence or presence of Vintec^®. On one hand, the results show that Vintec^® differentially modulates the expression of putative genes involved in hormonal signaling, especially those involved in auxin signaling. On the other hand, most significant gene expression modifications occur among secondary-metabolism-related genes, especially regarding phenylpropanoid metabolism and stilbene biosynthesis. Taken together, these results suggest that the biocontrol agent Vintec^® induces wood responses that counteract disease development.

Reducing herbicide use and leaching in agronomically performant maize-based cropping systems: An 8-year study

Irrigated maize-based Cropping Systems (CS) are questioned because of the high risk of herbicide transfer to water. An 8-year systemic experiment was conducted to i) compute a multi-performance comparison between a Conventional Maize Monoculture (MM_Conv) and four CS that aimed to reduce irrigation and herbicide leaching: MM_LI, a low-input MM using cover crop and Integrated Weed Management (IWM) techniques; MM_Still, a Strip-tillage MM using cover crop; MM_CT, a Conservation Tillage MM with cover crop; Maize-MSW, an IWM Maize rotated with Soybean and Wheat and ii) determine the main drivers and evaluate the influence of CS on herbicide leaching in maize. Drainage water was collected through 1-m depth lysimeter plates and analysed for 6 herbicide molecules and 1 degradation metabolite. MM_LI yielded 10.7 t ha^-1 close to MM_Conv (11.5 t ha^-1) despite a lower herbicide use (-57%) and irrigation (-21%). MM_LI and Maize-MSW had less drainage events compared to MM_Conv. MM_CT and MM_Still both yielded less (respectively 7.6 t ha^-1 and 6.2 t ha^-1) while their herbicide use increased (both +24%). Mean annual herbicide losses were 0.5 ± 1.0 g ha^-1 for MM_LI, 0.7 ± 1.2 g ha^-1 for Maize-MSW, 1.3 ± 2.1 g ha^-1 for MM_Still, 2.0 ± 4.8 g ha^-1 MM_Conv and 3.0 ± 9.6 g ha^-1 for MM_CT. Herbicide leaching remained variable but was consistently and mostly influenced by drainage volume. According to the CS, only 1.5 to 6.0 drainage events were responsible for 90% of the herbicide losses. High leaching peaks were identified for mesotrione and glyphosate and may indicate that preferential flows occurred, especially under MM_CT. Quantity applied had limited influence on herbicide leaching. To reduce the herbicide leaching risk, CS must concomitantly manage water quality and quantity through a combination of agroecological practices, as in MM_LI, a CS able to reach other technical objectives. Present study recommends assessing CS through a diversity of performance indicators.

Development of screening methods for functional characterization of UGTs from Stevia rebaudiana

Glycosylation is a key modification that contributes to determine bioactivity and bioavailability of plant natural products, including that of terpenoids and steviol glycosides (SVglys). It is mediated by uridine-diphosphate glycosyltransferases (UGTs), that achieve their activity by transferring sugars on small molecules. Thus, the diversity of SVglys is due to the number, the position and the nature of glycosylations on the hydroxyl groups in C-13 and C-19 of steviol. Despite the intense sweetener property of SVglys and the numerous studies conducted, the SVglys biosynthetic pathway remains largely unknown. More than 60 SVglys and 68 putative UGTs have been identified in Stevia rebaudiana. This study aims to provide methods to characterize UGTs putatively involved in SVglys biosynthesis. After agroinfiltration-based transient gene expression in Nicotiana benthamiana, functionality of the recombinant UGT can be tested simply and directly in plants expressing it or from a crude extract. The combined use of binary vectors from pGWBs series to produce expression vectors containing the stevia's UGT, enables functionality testing with many substrates as well as other applications for further analysis, including subcellular localization.

UGT76G1 polymorphism in Stevia rebaudiana: New variants for steviol glycosides conjugation

Steviol glycosides (SVglys) are secondary metabolites derived from terpenoids exhibiting high-sweetening properties produced in Stevia rebaudiana leaves. Their great diversity is due to the number, the position and the nature of glycosylations on the steviol aglycone. Steviol conjugation is mediated by uridine-diphosphate glycosyltransferases (UGTs). Four UGTs have been clearly identified as involved in SVglys metabolism: UGT74G1, UGT85C2, UGT76G1 and UGT73E1. Natural non-functional mutants with nonsense codon have yet been observed for UGT76G1. To investigate the variability of UGT76G1 functionality, natural mutants with low or no content of rebaudioside A and C were identified in a germplasm collection of Stevia rebaudiana. These compounds are known to be the direct products of UGT76G1 and their biosynthesis is governed by a single gene at the locus Rae (Rebaudioside A enablement). Crosses were done with remarkable accessions including phenotypes with low (0-3%) and high proportions (70%) of rebaudioside A and C, to investigate the functionality of the Rae locus in the parents. Seven variants of UGT76G1 were found, among them 4 lead to a functional protein and 3 lead to non-functional isoforms. Five of these variants are new. We found that non-functionality of UGT76G1 towards SVglys is not due to a premature nonsense codon, which appears to be an extreme case to explain the loss of functionality of an UGT. Variations in steviol glycoside profile in stevia leaves is partly due to UGT76G1 polymorphism: amino acid substitutions in parts of the protein involved in the substrate specificity can be found by sequence comparison.

Physicochemical characterization and study of molar mass of industrial gelatins by AsFlFFF-UV/MALS and chemometric approach

Industrial gelatins have different physicochemical properties that mainly depend of the raw materials origin and the extraction conditions. These properties are closely related to the molar mass distribution of these gelatins. Several methods exist to characterize molar mass distribution of polymer, including the Asymmetrical Flow Field Flow Fractionation method. The goal of this study is to analyze the relationship between physicochemical properties and the gelatins molar mass distribution obtained by Asymmetrical Flow Field Flow Fractionation. In this study, 49 gelatins samples extracted from pig skin are characterized in terms of gel strength and viscosity and their molar mass distribution are analyzed by Asymmetrical Flow Field Flow Fractionation coupled to an Ultraviolet and Multi Angle Light Scattering detector. This analytical method is an interesting tool for studying, simultaneously, the primary chains and the high-molar-mass fraction corresponding to the polymer chains. Correlation analysis between molar mass distribution data from the different fractions highlights the importance of high molar mass polymer chains to explain the gel strength and viscosity of gelatins. These results are confirmed by an additional chemometric approach based on the UV absorbance of gelatin fractograms to predict gel strength (r²Cal = 0.85) and viscosity (r²Cal = 0.79).

Accounting for biotic spatial variability in fields: Case of resistance screening against sunflower Verticillium wilt

In breeding for disease resistance, the magnitude of the genetic response is difficult to appreciate because of environmental stresses that interact with the plant genotype. We discuss herein the fundamental problems in breeding for disease resistance with the aim being to better understand the interactions between plant, pathogen, and spatial patterns. The goal of this study is to fine tune breeding decisions by incorporating spatial patterns of such biotic factors into the definition of disease-occurrence probability. We use a preexisting statistics method based on geostatistics for a descriptive analysis of biotic factors for trial quality control. The plant-population structure used for spatial-pattern analysis consists of two F1-hybrid cultivars, defined as symptomatic and asymptomatic controls with respect to the studied pathogen. The controls are inserted at specific locations to establish a grid arrangement over the field that include the F1-hybrid cultivars under evaluation. We characterize the spatial structure of the pathogen population and of the general plant environment-with undetermined but present abiotic constraints-not by using direct notation such as flower time or rainfall but by using plant behavior (i.e., leaf symptom severity, indirect notation). The analysis indicates areas with higher or lower risk of disease and reveals a correlation between the symptomatic control and the effective level of disease for sunflowers. This result suggests that the pathogen and/or abiotic components are major factors in determining the probability that a plant develops the disease, which could lead to a misinterpretation of plant resistance.

Intensified Separation of Steviol Glycosides from a Crude Aqueous Extract of Stevia rebaudiana Leaves Using Centrifugal Partition Chromatography

Aqueous extracts of Stevia rebaudiana leaves have been approved since 2008 by the Joint Expert Committee for Food Additives as sugar substitutes in many food and beverages in Western and Far East Asian countries. The compounds responsible for the natural sweetness of Stevia leaves include a diversity of diterpenoid glycosides derived from a steviol skeleton. These steviol glycosides also exhibit a low calorific value as well as promising therapeutic applications, particularly for the treatment of sugar metabolism disturbances. In this work, centrifugal partition chromatography is proposed as an efficient technical alternative to purify steviol glycosides from crude aqueous extracts of Stevia leaves on a multigram scale. Two different commercial instruments, including an ASCPC250® and a FCPE300® made of columns containing 1890 and 231 twin-cells, respectively, were evaluated and compared. All experiments were performed with a polar biphasic solvent system composed of ethyl acetate, n-butanol, and water in a gradient elution mode. When using the 1890 partition cell centrifugal partition chromatography column of 250 mL, 42 mg of stevioside, 68 mg of dulcoside A, and 172 mg of rebaudioside A, three major constituents of the initial extract were obtained from 1 g of the initial mixture at purities of 81%, 83%, and 99%, respectively. The productivity was further improved by intensifying the procedure on the 231 partition cell centrifugal partition chromatography column of 303 mL with the sample mass loading increased up to 5 g, resulting in the recovery of 1.2 g of stevioside, 100 mg of dulcoside A, and 1.1 g of rebaudioside A at purities of 79%, 62%, and 98%, respectively. The structures of the isolated compounds were validated by HPLC-UV, ESI-MS, (1)H, and (13)C NMR analyses. Altogether, the results demonstrate that the column design (i.e., the partition cell number) is an important aspect to be considered for a larger scale centrifugal partition chromatography isolation of Stevia-derived natural sweeteners.

Nitrogen Limitation Alters Biomass Production but Enhances Steviol Glycoside Concentration in Stevia rebaudiana Bertoni

The need for medicinal and aromatic plants for industrial uses creates an opportunity for farmers to produce alternative crops. Stevia rebaudiana Bertoni, a perennial shrub originating from Paraguay, is of increasing interest as a source of zero-calorie natural sweeteners: the steviol glycosides (SVglys). The aim of this study was to investigate the relevance of nitrogen (N) supply for leaf yield and for SVgly concentrations in leaves, which are the two major components of S. rebaudiana productivity. In this regard, the relationship between leaf N concentration, CO₂ assimilation, leaf production and SVgly accumulation was investigated. The experiments were conducted consecutively in growth-chamber (CC: controlled conditions), in greenhouse (SCC: semi-controlled conditions) and in field conditions (FC) on two genotypes. In CC and SCC, three levels of N fertilization were applied. Plants were grown on four locations in the FC experiment. Both N supply (CC and SCC) and location (FC) had a significant effect on N content in leaves. When light was not limiting (SCC and FC) N content in leaves was positively correlated with CO₂ assimilation rate and biomass accumulation. Irrespective of the growth conditions, N content in leaves was negatively correlated with SVgly content. However, increased SVgly content was correlated with a decreased ratio of rebaudioside A over stevioside. The evidence that the increased SVgly accumulation compensates for the negative effect on biomass production suggests that adequate SVgly productivity per plant may be achieved with relatively low fertilization.

Expression of flavonoid 6-hydroxylase candidate genes in normal and mutant soybean genotypes for glycitein content

Soybean seeds accumulate large amounts of isoflavones (genistein, daidzein and glycitein), secondary metabolites known for their phytoestrogenic activities. Isoflavone composition depends on the seed part and glycitein is almost found exclusively in hypocotyls. Moreover, two major phenotypes are encountered in soybean cultivars, with either low (35 %) or high (55 %) levels of glycitein in their hypocotyls. This trait was under a quasi-mendelian heredity, implicating at most one or two genes. A CYP71D9 cDNA displaying a flavonoid 6-hydroxylase (F6H) activity had previously been isolated from elicitor-induced soybean (Glycine max L.) cells. This enzyme allows the synthesis of the glycitein flavanone intermediate (6,7,4'- trihydroxyflavanone) by catalyzing the A-ring hydroxylation of liquiritigenin. In this study, the CYP71D9 gene (F6H1) and two other candidates (F6H2 and F6H3) were studied using contrasted soybean cultivars for glycitein content (0, 35, 55 and 80 %). Their expression was observed in chitosan elicited leaves. They encode P450 proteins of 496, 469 and 481 amino acids respectively and were expressed in leaves with or without elicitation. The expression patterns of these three genes were performed in cotyledons and hypocotyls at different developmental stages. F6H1 and F6H2 were not expressed in the developing seed. F6H3 was only expressed in hypocotyls. Its expression levels did not correlate with hypocotyls glycitein content, but it was not expressed in the null mutant for glycitein. Thus, this F6H3 gene is a good potential candidate for glycitein biosynthesis in soybean seed.

Effects of fermentation on the phytochemical composition and antioxidant properties of soy germ

Soy germ is a remarkable source of bioactive phytochemicals offering an interesting alternative as starting ingredient for fermented food. This work aimed to determine whether lactic acid bacteria fermentation of soy germ induces changes on its phytochemical composition. The antioxidant properties of fermented soy germ samples periodically taken during the fermentation process were evaluated and correlated with the concentration and structural modifications of isoflavones, saponins, phytosterols and tocopherols. Fermented soy germ extracts exhibited a higher inhibition effect against the superoxide anion radical, and lesser but significant ferric-reducing and DPPH radical scavenging effects compared with raw soy germ. By comparison to the traditional whole seed-based products, soy germ exhibits higher levels of isoflavones, saponins, phytosterols and tocopherols. All these phytochemicals contributed to the antioxidant capacity of soy germ and were conserved under lactic acid bacteria fermentation.

Use of a simplified HPLC-UV analysis for soyasaponin B determination: study of saponin and isoflavone variability in soybean cultivars and soy-based health food products

Soyasaponins are phytochemicals of major interest for health. Their identification and quantification remain difficult owing to the large number of structural isomers in soybeans and the lack of stable standards. In this study, a rapid method using high performance liquid chromatography (HPLC) using a UV detector (205 nm) was developed to identify and quantify soyasaponins belonging to group B and compare them with isoflavones in different soy materials. 2,3-Dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP)-conjugated soyasaponins were determined using external calibration or a molecular mass ratio after alkaline hydrolysis to cleave their DDMP moieties. The detection limit of soyasaponin I, used as a reference molecule to simplify the analysis, was 0.065 micromol/g. Soyasaponin contents in seven soybean varieties ranged from 13.20 to 42.40 micromol/g in the germ and from 2.76 to 6.43 micromol/g in the cotyledons. The within-day and between-days variation coefficients did not exceed 7.9 and 9.0%, respectively, for the major soyasaponins. Soyasaponin B quantification in different soy-based health supplements was reported along with measurements of their isoflavone content to provide information on the variability of these bioactive compounds among different types of soy food materials.

Quantification of isoflavones by capillary zone electrophoresis in soybean seeds: effects of variety and environment

Soybean isoflavones (genistin, daidzin, glycitin, and their malonyl forms and aglucons) are thought to be responsible for the astringent taste of soyfoods. Generally, HPLC with a methanol and water elution gradient is used for isoflavone quantification, but capillary zone electrophoresis (CZE) has been used more recently to separate several flavonoids in plant extracts. We present the results of CZE analysis of isoflavones in soybean extracts. Conditions for separation by using CZE were optimized for analysis of soybean isoflavones. We compared the results of extraction at different temperatures and with different compositions of solvent. Total extraction of isoflavones was not affected by temperature but was affected by composition of the solvent. Malonyl forms of isoflavones were thermally unstable. We analyzed the isoflavone content of different varieties of soybean seeds sown on different dates. Total isoflavone content varied among different varieties and with sowing dates. Interactions between the variety and the sowing date also affected isoflavone composition. We conclude that the variety of soybean seed and environmental growing conditions, such as sowing date, can contribute to seed quality by reducing its isoflavone content, modifying its isoflavone composition, or both.