Structure and genetic diversity of Canadian Maritimes wild hops.

Studies on the northeastern American native hops (Humulus lupulus ssp. lupuloides) from the Canadian Maritimes are scarce. This study aimed to evaluate the genetic structure and diversity among 25 wild-collected hops from three Canadian Maritime provinces using microsatellite (simple sequence repeat (SSR)) markers. Based on 43 SSR markers, four distinct subgroups were found, with a low molecular variance (19%) between subgroups and a high variance (81%) within subgroups. The Nei's unbiased genetic distance between clusters ranged from 0.01 to 0.08, the genetic distance between clusters 2 and 3 being the farthest and that between clusters 1 and 2 the closest. Cluster 2 captured the highest overall diversity. A total of 18 SSR markers clearly discriminated hop clones by detecting putative subspecies-specific haplotypes, differentiating clones of native-wild H. lupulus ssp. lupuloides from the naturalized old and modern hop cultivars. Seven of the 18 SSR markers also differentiated two clones from the same site from one another. The study is the first, using molecular markers, to identify SSR markers with potential for intellectual property protection in Canadian Maritimes hops. The SSR markers herein used can be prime tools for hop breeders and growers in the region.

The Genetic Dissection of Nitrogen Use-Related Traits in Flax (Linum usitatissimum L.) at the Seedling Stage through the Integration of Multi-Locus GWAS, RNA-seq and Genomic Selection.

Nitrogen (N), the most important macro-nutrient for plant growth and development, is a key factor that determines crop yield. Yet its excessive applications pollute the environment and are expensive. Hence, studying nitrogen use efficiency (NUE) in crops is fundamental for sustainable agriculture. Here, an association panel consisting of 123 flax accessions was evaluated for 21 NUE-related traits at the seedling stage under optimum N (N+) and N deficiency (N-) treatments to dissect the genetic architecture of NUE-related traits using a multi-omics approach integrating genome-wide association studies (GWAS), transcriptome analysis and genomic selection (GS). Root traits exhibited significant and positive correlations with NUE under N- conditions (r = 0.33 to 0.43, p < 0.05). A total of 359 QTLs were identified, accounting for 0.11% to 23.1% of the phenotypic variation in NUE-related traits. Transcriptomic analysis identified 1034 differentially expressed genes (DEGs) under contrasting N conditions. DEGs involved in N metabolism, root development, amino acid transport and catabolism and others, were found near the QTLs. GS models to predict NUE stress tolerance index (NUE_STI) trait were tested using a random genome-wide SNP dataset and a GWAS-derived QTLs dataset. The latter produced superior prediction accuracy (r = 0.62 to 0.79) compared to the genome-wide SNP marker dataset (r = 0.11) for NUE_STI. Our results provide insights into the QTL architecture of NUE-related traits, identify candidate genes for further studies, and propose genomic breeding tools to achieve superior NUE in flax under low N input.

Genome-wide genetic architecture for plant maturity and drought tolerance in diploid potatoes.

Cultivated potato (Solanum tuberosum) is known to be highly susceptible to drought. With climate change and its frequent episodes of drought, potato growers will face increased challenges to achieving their yield goals. Currently, a high proportion of untapped potato germplasm remains within the diploid potato relatives, and the genetic architecture of the drought tolerance and maturity traits of diploid potatoes is still unknown. As such, a panel of 384 ethyl methanesulfonate-mutagenized diploid potato clones were evaluated for drought tolerance and plant maturity under field conditions. Genome-wide association studies (GWAS) were conducted to dissect the genetic architecture of the traits. The results obtained from the genetic structure analysis of the panel showed five main groups and seven subgroups. Using the Genome Association and Prediction Integrated Tool-mixed linear model GWAS statistical model, 34 and 17 significant quantitative trait nucleotides (QTNs) were found associated with maturity and drought traits, respectively. Chromosome 5 carried most of the QTNs, some of which were also detected by using the restricted two-stage multi-locus multi-allele-GWAS haploblock-based model, and two QTNs were found to be pleiotropic for both maturity and drought traits. Using the non-parametric U-test, one and three QTNs, with 5.13%-7.4% phenotypic variations explained, showed favorable allelic effects that increase the maturity and drought trait values. The quantitaive trait loci (QTLs)/QTNs associated with maturity and drought trait were found co-located in narrow (0.5-1 kb) genomic regions with 56 candidate genes playing roles in plant development and senescence and in abiotic stress responses. A total of 127 potato clones were found to be late maturing and tolerant to drought, while nine were early to moderate-late maturing and tolerant to drought. Taken together, the data show that the studied germplasm panel and the identified candidate genes are prime genetic resources for breeders and biologists in conventional breeding and targeted gene editing as climate adaptation tools.

Choice of cover crop influences soil fungal and bacterial communities in Prince Edward Island, Canada.

Soil fungal and bacterial communities play various roles in agroecosystems and are significantly influenced by agricultural management practices. Currently, little is known about the effects of selected cover crops on soil fungal and bacterial communities in no-till systems. In this study, eight cover crops, three mixed crops, and an unmanaged fallow control were evaluated over 2 years for their effects on the soil microbiome. Internal transcribed spacer (ITS) and 16S rRNA amplicon sequencing was performed to characterize fungal and bacterial communities in the soil during the cover crop growing season, and in the subsequent year. Fungal and bacterial alpha diversity significantly increased over time and were influenced in the subsequent growing season by choice of cover crops. Some fungal and bacterial trophic and functional groups were also affected by crop choice. Fungal pathotroph abundance was positively associated with oilseed radish, alfalfa, and phacelia, but negatively associated with sorghum-sudangrass. Beneficial symbiotrophic fungi and functional nitrification-related bacterial groups were also associated with sorghum-sudangrass and buckwheat. These findings suggest that choice of cover crops influences the soil microbial community composition and may impact plant health in the subsequent crops.

Aluminum in plant: Benefits, toxicity and tolerance mechanisms.

Aluminum (Al) is the third most ubiquitous metal in the earth's crust. A decrease in soil pH below 5 increases its solubility and availability. However, its impact on plants depends largely on concentration, exposure time, plant species, developmental age, and growing conditions. Although Al can be beneficial to plants by stimulating growth and mitigating biotic and abiotic stresses, it remains unknown how Al mediates these effects since its biological significance in cellular systems is still unidentified. Al is considered a major limiting factor restricting plant growth and productivity in acidic soils. It instigates a series of phytotoxic symptoms in several Al-sensitive crops with inhibition of root growth and restriction of water and nutrient uptake as the obvious symptoms. This review explores advances in Al benefits, toxicity and tolerance mechanisms employed by plants on acidic soils. These insights will provide directions and future prospects for potential crop improvement.

Comparative transcriptome expression analysis in susceptible and resistant potato (Solanum tuberosum) cultivars to common scab (Streptomyces scabies) revealed immune priming responses in the incompatible interaction.

Common scab disease in potato has become a widespread issue in major potato production areas, leading to increasing economic losses. Varietal resistance is seen as a viable and long-term scab management strategy. However, the genes and mechanisms of varietal resistance are unknown. In the current study, a comparative RNA transcriptome sequencing and differential gene signaling and priming sensitization studies were conducted in two potato cultivars that differ by their response to common scab (Streptomyces scabies), for unraveling the genes and pathways potentially involved in resistance within this pathosystem. We report on a consistent and contrasted gene expression pattern from 1,064 annotated genes differentiating a resistant (Hindenburg) and a susceptible (Green Mountain) cultivars, and identified a set of 273 co-regulated differentially expressed genes in 34 pathways that more likely reflect the genetic differences of the cultivars and metabolic mechanisms involved in the scab pathogenesis and resistance. The data suggest that comparative transcriptomic phenotyping can be used to predict scab lesion phenotype in breeding lines using mature potato tuber. The study also showed that the resistant cultivar, Hindenburg, has developed and maintained a capacity to sense and prime itself for persistent response to scab disease over time, and suggests an immune priming reaction as a mechanism for induced-resistance in scab resistant potato cultivars. The set of genes identified, described, and discussed in the study paves the foundation for detailed characterizations towards tailoring and designing procedures for targeted gene knockout through gene editing and phenotypic evaluation.

Induced Mutagenesis in UGT74S1 Gene Leads to Stable New Flax Lines with Altered Secoisolariciresinol Diglucoside (SDG) Profiles.

Flax secoisolariciresinol (SECO) diglucoside (SDG) lignan is an emerging natural product purported to prevent chronic diseases in humans. SECO, the aglycone form of SDG, has shown higher intestinal cell absorption but it is not accumulated naturally in planta. Recently, we have identified and characterized a UDP-glucosyltransferase gene, UGT74S1, that glucosylates SECO into its monoglucoside (SMG) and SDG forms when expressed in yeast. However, whether this gene is unique in controlling SECO glucosylation into SDG in planta is unclear. Here, we report on the use of UGT74S1 in reverse and forward genetics to characterize an ethyl methane sulfonate (EMS) mutagenized flax population from cultivar CDC Bethune and consisting of 1996 M2 families. EMS mutagenesis generated 73 SNP variants causing 79 mutational events in the UGT74S1 exonic regions of 93 M2 families. The mutation frequency in the exonic regions was determined to be one per 28 Kb. Of these mutations, 13 homozygous missense mutations and two homozygous nonsense mutations were observed and all were transmitted into the M3 and M4 generations. Forward genetics screening of the population showed homozygous nonsense mutants completely lacking SDG biosynthesis while the production of SMG was observed only in a subset of the M4 lines. Heterozygous or homozygous M4 missense mutants displayed a wide range of SDG levels, some being greater than those of CDC Bethune. No additional deleterious mutations were detected in these mutant lines using a panel of 10 other genes potentially involved in the lignan biosynthesis. This study provides further evidence that UGT74S1 is unique in controlling SDG formation from SECO and this is the first report of non-transgenic flax germplasm with simultaneous knockout of SDG and presence of SMG in planta.

Genetic analyses using GGE model and a mixed linear model approach, and stability analyses using AMMI bi-plot for late-maturity alpha-amylase activity in bread wheat genotypes.

Low falling number and discounting grain when it is downgraded in class are the consequences of excessive late-maturity α-amylase activity (LMAA) in bread wheat (Triticum aestivum L.). Grain expressing high LMAA produces poorer quality bread products. To effectively breed for low LMAA, it is necessary to understand what genes control it and how they are expressed, particularly when genotypes are grown in different environments. In this study, an International Collection (IC) of 18 spring wheat genotypes and another set of 15 spring wheat cultivars adapted to South Dakota (SD), USA were assessed to characterize the genetic component of LMAA over 5 and 13 environments, respectively. The data were analysed using a GGE model with a mixed linear model approach and stability analysis was presented using an AMMI bi-plot on R software. All estimated variance components and their proportions to the total phenotypic variance were highly significant for both sets of genotypes, which were validated by the AMMI model analysis. Broad-sense heritability for LMAA was higher in SD adapted cultivars (53%) compared to that in IC (49%). Significant genetic effects and stability analyses showed some genotypes, e.g. 'Lancer', 'Chester' and 'LoSprout' from IC, and 'Alsen', 'Traverse' and 'Forefront' from SD cultivars could be used as parents to develop new cultivars expressing low levels of LMAA. Stability analysis using an AMMI bi-plot revealed that 'Chester', 'Lancer' and 'Advance' were the most stable across environments, while in contrast, 'Kinsman', 'Lerma52' and 'Traverse' exhibited the lowest stability for LMAA across environments.

UGT74S1 is the key player in controlling secoisolariciresinol diglucoside (SDG) formation in flax.

BACKGROUND: Flax lignan, commonly known as secoisolariciresinol (SECO) diglucoside (SDG), has recently been reported with health-promoting activities, including its positive impact in metabolic diseases. However, not much was reported on the biosynthesis of SDG and its monoglucoside (SMG) until lately. Flax UGT74S1 was recently reported to sequentially glucosylate SECO into SMG and SDG in vitro. However, whether this gene is the only UGT achieving SECO glucosylation in flax was not known. RESULTS: Flax genome-wide mining for UGTs was performed. Phylogenetic and gene duplication analyses, heterologous gene expression and enzyme assays were conducted to identify family members closely related to UGT74S1 and to establish their roles in SECO glucosylation. A total of 299 different UGTs were identified, of which 241 (81%) were duplicated. Flax UGTs diverged 2.4-153.6 MYA and 71% were found to be under purifying selection pressure. UGT74S1, a single copy gene located on chromosome 7, displayed no evidence of duplication and was deemed to be under positive selection pressure. The phylogenetic analysis identified four main clusters where cluster 4, which included UGT74S1, was the most diverse. The duplicated UGT74S4 and UGT74S3, located on chromosomes 8 and 14, respectively, were the most closely related to UGT74S1 and were differentially expressed in different tissues. Heterologous expression levels of UGT74S1, UGT74S4 and UGT74S3 proteins were similar but UGT74S4 and UGT74S3 glucosylation activity towards SECO was seven fold less than UGT74S1. In addition, they both failed to produce SDG, suggesting neofunctionalization following their divergence from UGT74S1. CONCLUSIONS: We showed that UGT74S1 is closely related to two duplicated genes, UGT74S4 and UGT74S3 which, unlike UGT74S1, failed to glucosylate SMG into SDG. The study suggests that UGT74S1 may be the key player in controlling SECO glucosylation into SDG in flax although its closely related genes may also contribute to a minor extent in supplying the SMG precursor to UGT74S1.

Histidine 352 (His352) and tryptophan 355 (Trp355) are essential for flax UGT74S1 glucosylation activity toward secoisolariciresinol.

Flax secoisolariciresinol diglucoside (SDG) lignan is a natural phytoestrogen for which a positive role in metabolic diseases is emerging. Until recently however, much less was known about SDG and its monoglucoside (SMG) biosynthesis. Lately, flax UGT74S1 was identified and characterized as an enzyme sequentially glucosylating secoisolariciresinol (SECO) into SMG and SDG when expressed in yeast. However, the amino acids critical for UGT74S1 glucosyltransferase activity were unknown. A 3D structural modeling and docking, site-directed mutagenesis of five amino acids in the plant secondary product glycosyltransferase (PSPG) motif, and enzyme assays were conducted. UGT74S1 appeared to be structurally similar to the Arabidopsis thaliana UGT72B1 model. The ligand docking predicted Ser357 and Trp355 as binding to the phosphate and hydroxyl groups of UDP-glucose, whereas Cys335, Gln337 and Trp355 were predicted to bind the 7-OH, 2-OCH3 and 17-OCH3 of SECO. Site-directed mutagenesis of Cys335, Gln337, His352, Trp355 and Ser357, and enzyme assays revealed an alteration of these binding sites and a significant reduction of UGT74S1 glucosyltransferase catalytic activity towards SECO and UDP-glucose in all mutants. A complete abolition of UGT74S1 activity was observed when Trp355 was substituted to Ala355 and Gly355 or when changing His352 to Asp352, and an altered metabolite profile was observed in Cys335Ala, Gln337Ala, and Ser357Ala mutants. This study provided for the first time evidence that Trp355 and His352 are critical for UGT74S1's glucosylation activity toward SECO and suggested the possibility for SMG production in vitro.

Identification and functional characterization of a flax UDP-glycosyltransferase glucosylating secoisolariciresinol (SECO) into secoisolariciresinol monoglucoside (SMG) and diglucoside (SDG).

BACKGROUND: Lignans are a class of diphenolic nonsteroidal phytoestrogens often found glycosylated in planta. Flax seeds are a rich source of secoisolariciresinol diglucoside (SDG) lignans. Glycosylation is a process by which a glycosyl group is covalently attached to an aglycone substrate and is catalyzed by uridine diphosphate glycosyltransferases (UGTs). Until now, very little information was available on UGT genes that may play a role in flax SDG biosynthesis. Here we report on the identification, structural and functional characterization of 5 putative UGTs potentially involved in secoisolariciresinol (SECO) glucosylation in flax. RESULTS: Five UGT genes belonging to the glycosyltransferases' family 1 (EC 2.4.x.y) were cloned and characterized. They fall under four UGT families corresponding to five sub-families referred to as UGT74S1, UGT74T1, UGT89B3, UGT94H1, UGT712B1 that all display the characteristic plant secondary product glycosyltransferase (PSPG) conserved motif. However, diversity was observed within this 44 amino acid sequence, especially in the two peptide sequences WAPQV and HCGWNS known to play a key role in the recognition and binding of diverse aglycone substrates and in the sugar donor specificity. In developing flax seeds, UGT74S1 and UGT94H1 showed a coordinated gene expression with that of pinoresinol-lariciresinol reductase (PLR) and their gene expression patterns correlated with SDG biosynthesis. Enzyme assays of the five heterologously expressed UGTs identified UGT74S1 as the only one using SECO as substrate, forming SECO monoglucoside (SMG) and then SDG in a sequential manner. CONCLUSION: We have cloned and characterized five flax UGTs and provided evidence that UGT74S1 uses SECO as substrate to form SDG in vitro. This study allowed us to propose a model for the missing step in SDG lignan biosynthesis.

Dietary flaxseed intake exacerbates acute colonic mucosal injury and inflammation induced by dextran sodium sulfate.

Flaxseed (FS), a dietary oilseed, contains a variety of anti-inflammatory bioactives, including fermentable fiber, phenolic compounds (lignans), and the n-3 polyunsaturated fatty acid (PUFA) α-linolenic acid. The objective of this study was to determine the effects of FS and its n-3 PUFA-rich kernel or lignan- and soluble fiber-rich hull on colitis severity in a mouse model of acute colonic inflammation. C57BL/6 male mice were fed a basal diet (negative control) or a basal diet supplemented with 10% FS, 6% kernel, or 4% hull for 3 wk prior to and during colitis induction via 5 days of 2% (wt/vol) dextran sodium sulfate (DSS) in their drinking water (n = 12/group). An increase in anti-inflammatory metabolites (hepatic n-3 PUFAs, serum mammalian lignans, and cecal short-chain fatty acids) was associated with consumption of all FS-based diets, but not with anti-inflammatory effects in DSS-exposed mice. Dietary FS exacerbated DSS-induced acute colitis, as indicated by a heightened disease activity index and an increase in colonic injury and inflammatory biomarkers [histological damage, apoptosis, myeloperoxidase, inflammatory cytokines (IL-6 and IL-1ß), and NF-κB signaling-related genes (Nfkb1, Ccl5, Bcl2a1a, Egfr, Relb, Birc3, and Atf1)]. Additionally, the adverse effect of the FS diet was extended systemically, as serum cytokines (IL-6, IFNγ, and IL-1ß) and hepatic cholesterol levels were increased. The adverse effects of FS were not associated with alterations in fecal microbial load or systemic bacterial translocation (endotoxemia). Collectively, this study demonstrates that although consumption of a 10% FS diet enhanced the levels of n-3 PUFAs, short-chain polyunsaturated fatty acids, and lignans in mice, it exacerbated DSS-induced colonic injury and inflammation.

Prenatal alcohol exposure alters phosphorylation and glycosylation of proteins in rat offspring liver.

To gain more insights into the translational and PTM that occur in rat offspring exposed to alcohol in utero, 2-D PAGE with total, phospho- and glycoprotein staining and MALDI-MS/MS and database searching were conducted. The results, based on fold-change expression, revealed a down-regulation of total protein expression by prenatal alcohol exposure in 7-day-old and 3-month-old rats. There was an up-regulation of protein phosphorylation but a down-regulation of glycosylation by prenatal alcohol exposure in both age groups. Of 31 protein spots examined per group, differentially expressed proteins were identified as ferritin light chain, aldo-keto reductase, tumor rejection antigen gp96, fructose-1,6-bisphosphatase, glycerol-3-phosphate dehydrogenase, malate dehydrogenase, and gamma-actin. Increased phosphorylation was observed in proteins such as calmodulin, gluthatione S-transferase, glucose regulated protein 58, alpha-enolase, eukaryotic translation elongation factor 1 beta-2, riboprotein large P2, agmatinase, ornithine carbamoyltransferase, quinolinate phosphoribosyltransferase, formimidoyltransferase cyclodeaminase, and actin. In addition, glycosylation of adenosine kinase, adenosylhomocysteine hydrolase, and 3-hydroxyanthranilate dioxygenase was reduced. Pathways affected by these protein alterations include cell signaling, cellular stress, protein synthesis, cytoskeleton, as well as glucose, aminoacid, adenosine and energy metabolism. The activity of the gluconeogenic enzyme fructose-1,6-bisphosphatase was elevated by prenatal alcohol. The observations may have important physiological implications.

Assessment of molecular diversity at QTLs for preharvest sprouting resistance in wheat using microsatellite markers.

Breeding for preharvest sprouting (PHS) resistance is of great interest in wheat-growing areas where high rainfall occurs during grain ripening and harvest. We have characterized 32 wheat accessions using 33 microsatellite markers flanking PHS quantitative trait loci (QTLs) previously identified on group 3, 4, 5, and 6 chromosomes of hexaploid wheat. A total of 229 alleles, with an average of 6.94 alleles per marker, were observed among the 32 wheat lines. The polymorphic information content (PIC) was estimated and ranged between 0.25 and 0.90, with an average of 0.67. A cluster analysis revealed 3 main clusters and 3 singlet wheat lines, which is in agreement with pedigree-based relationships, seed coat colour, and origin. Canadian wheat accessions were subdivided into 4 sub-clusters based on pedigree and wheat classes. Grouping of preharvest sprouting germplasm into clusters was consistent with cluster-specific allele diversity observed in the PHS-resistant lines AUS1408, Red-RL4137, White-RL4137, and Kenya321. The implications of these findings in white wheat breeding for PHS tolerance are discussed.

Temporal gene expression profiling of the wheat leaf rust pathosystem using cDNA microarray reveals differences in compatible and incompatible defence pathways.

In this study, we detail the construction of a custom cDNA spotted microarray containing 7728 wheat ESTs and the use of the array to identify host genes that are differentially expressed upon challenges with leaf rust fungal pathogens. Wheat cultivar RL6003 (Thatcher Lr1) was inoculated with Puccinia triticina virulence phenotypes BBB (incompatible) or TJB (7-2) (compatible) and sampled at four different time points (3, 6, 12, and 24 hours) after inoculation. Transcript expression levels relative to a mock treatment were measured. One hundred ninety two genes were found to have significantly altered expression between the compatible and incompatible reactions. Among those were genes involved in photosynthesis, the production of reactive oxygen species, ubiquitination, signal transduction, as well as in the shikimate/phenylpropanoid pathway. These data indicate that various metabolic pathways are affected, some of which might be used by RL6003 to mount a coordinated defense against an incompatible fungal pathogen.

Gene expression of stearoyl-ACP desaturase and delta12 fatty acid desaturase 2 is modulated during seed development of flax (Linum usitatissimum).

Flax's recent popularity in human and animal foods is mostly due to its desirable FA composition. Flax is an excellent source of omega-3 FA, which have been shown to have many health benefits. To date, little is known about the genetic and environmental factors that control the FA composition of flax seeds. To elucidate some of the important genetic components, reverse transcriptase (RT)-PCR and real-time PCR were used to determine the expression profiles of two key FA biosynthetic genes during seed development. Plants of flax cultivar AC McDuff were grown under field conditions, and RNA was extracted from ovaries and developing bolls collected from 2 d after anthesis (DAA) to maturity. Desaturation enzymes stearoyl-ACP desaturase (SAD) and delta12 FA desaturase 2 (FAD2) were both expressed in ovaries, and their expression was differentially modulated throughout seed development. SAD was most highly expressed in ovaries. Its expression quickly decreased until 4 DAA; this was followed by a slight peak at 8 DAA, only to return to relatively low levels of expression in maturing bolls, ranging from 2.1% to 4.5% relative to the level observed in ovaries. FAD2 expression displayed a different temporal pattern. While expression of FAD2 did decrease in the early stages of seed development, expression increased starting at 8 DAA, peaking at 16 DAA, when it was 158% relative to the level observed in ovaries. FAD2, which desaturates oleic acid (18:1cisdelta9) into linoleic acid (18:2cisdelta9,12), is therefore controlled at the transcription level. To relate enzyme expression with FA profile, GC was performed on the same subsamples used for RT-PCR and real-time PCR, and proportions of palmitic, stearic, oleic, linoleic, and linolenic acids were determined for the same developmental stages. Although FAD2 expression increased from 8 to 16 DAA, relative changes in linoleic acid (18:2cis delta9,12) were not observed. However, linolenic acid (ALA; alpha-18:3; 18:3cisdelta9,12,15) levels increased steadily, meaning that linoleic acid (18:2cisdelta9,12) is a transient substrate converted by FAD3 as quickly as it is produced by FAD2. Phenotypes are the result of genotypes, environment, and the interaction of the two. To evaluate the environmental impact on the production of FA in flax, FA profiles were assessed in a total of four environments (two locations, two years). Warm and dry environmental conditions resulted in lower levels of PUFA 18:2cisdelta9,12 and 18:3cisdelta9,12,15, and higher levels of 18:1 cisdelta9. FAD2 expression and/or activity may therefore be affected by the environment.

Suppression of induced resistance in cucumber through disruption of the flavonoid pathway.

ABSTRACT In this study, cucumber plants (Cucumis sativus) expressing induced resistance against powdery mildew (caused by Podosphaera xanthii) were infiltrated with inhibitors of cinnamate 4-hydroxylase, 4-coumarate:CoA ligase (4CL), and chalcone synthase (CHS) to evaluate the role of flavonoid phytoalexin production in induced disease resistance. Light and transmission electron microscopy demonstrated ultrastructural changes in inhibited plants, and biochemical analyses determined levels of CHS and beta-glucosidase enzyme activity and 4CL protein accumulation. Our results showed that elicited plants displayed a high level of induced resistance. In contrast, down regulation of CHS, a key enzyme of the flavonoid pathway, resulted in nearly complete suppression of induced resistance, and microscopy confirmed the development of healthy fungal haustoria within these plants. Inhibition of 4CL ligase, an enzyme largely responsible for channeling phenylpropanoid metabolites into the lignin pathway, had little effect on induced disease resistance. Biochemical analyses revealed similar levels of 4CL protein accumulation for all treatments, suggesting no alterations of nontargeted functions within inhibited plants. Collectively, the results of this study support the idea that induced resistance in cucumber is largely correlated with rapid de novo biosynthesis of flavonoid phytoalexin compounds.