Genetic diversity of SAD and FAD genes responsible for the fatty acid composition in flax cultivars and lines

BACKGROUND

Flax (Linum usitatissimum L.) is grown for fiber and seed in many countries. Flax cultivars differ in the oil composition and, depending on the ratio of fatty acids, are used in pharmaceutical, food, or paint industries. It is known that genes of SAD (stearoyl-ACP desaturase) and FAD (fatty acid desaturase) families play a key role in the synthesis of fatty acids, and some alleles of these genes are associated with a certain composition of flax oil. However, data on genetic polymorphism of these genes are still insufficient.

RESULTS

On the basis of the collection of the Institute for Flax (Torzhok, Russia), we formed a representative set of 84 cultivars and lines reflecting the diversity of fatty acid composition of flax oil. An approach for the determination of full-length sequences of SAD1, SAD2, FAD2A, FAD2B, FAD3A, and FAD3B genes using the Illumina platform was developed and deep sequencing of the 6 genes in 84 flax samples was performed on MiSeq. The obtained high coverage (about 400x on average) enabled accurate assessment of polymorphisms in SAD1, SAD2, FAD2A, FAD2B, FAD3A, and FAD3B genes and evaluation of cultivar/line heterogeneity. The highest level of genetic diversity was observed for FAD3A and FAD3B genes - 91 and 62 polymorphisms respectively. Correlation analysis revealed associations between particular variants in SAD and FAD genes and predominantly those fatty acids whose conversion they catalyze: SAD - stearic and oleic acids, FAD2 - oleic and linoleic acids, FAD3 - linoleic and linolenic acids. All except one low-linolenic flax cultivars/lines contained both the substitution of tryptophan to stop codon in the FAD3A gene and histidine to tyrosine substitution in the FAD3B gene, while samples with only one of these polymorphisms had medium content of linolenic acid and cultivars/lines without them were high-linolenic.

CONCLUSIONS

Genetic polymorphism of SAD and FAD genes was evaluated in the collection of flax cultivars and lines with diverse oil composition, and associations between particular polymorphisms and the ratio of fatty acids were revealed. The achieved results are the basis for the development of marker-assisted selection and DNA-based certification of flax cultivars.

Molecular identification and functional characterization of a cyanogenic glucosyltransferase from flax (Linum unsitatissimum)

Flax seed has become consumers’ choice for not only polyunsaturated alpha-linolenic fatty acid but also nutraceuticals such as lignans and soluble fiber. There is, however, a major drawback of flax as a source of functional food since the seeds contain significant level of cyanogenic glucosides. The final step of cyanogenic glucoside biosynthesis is mediated by UDP-glucose dependent glucosyltransferase. To date, no flax cyanogenic glucosyl transferase genes have been reported with verified biochemical functionality. Here we present a study on the identification and enzymatic characterization of a first flax cyanogenic glucosyltransferase, LuCGT1. We show that LuCGT1 was highly active towards both aliphatic and aromatic substrates. The LuCGT1 gene is expressed in leaf tissues as well as in developing seeds, and its expression level was drastically reduced in flax mutant lines low in cyanogenic glucosides. Identification of LuCGT1 provides a molecular handle for developing gene specific markers for targeted breeding of low cyanogenic glucosides in flax.

Flax rhamnogalacturonan lyases: phylogeny, differential expression and modeling of protein structure

Rhamnogalacturonan lyases (RGLs; EC 4.2.2.23) degrade the rhamnogalacturonan I (RG-I) backbone of pectins present in the plant cell wall. These enzymes belong to polysaccharide lyase family 4, members of which are mainly from plants and plant pathogens. RGLs are investigated, as a rule, as pathogen 'weapons' for plant cell wall degradation and subsequent infection. Despite the presence of genes annotated as RGLs in plant genomes and the presence of substrates for enzyme activity in plant cells, evidence supporting the involvement of this enzyme in certain processes is limited. The differential expression of some RGL genes in flax (Linum usitatissimum L.) tissues, revealed in our previous work, prompted us to carry out a total revision (phylogenetic analysis, analysis of expression and protein structure modeling) of all the sequences of flax predicted as coding for RGLs. Comparison of the expressions of LusRGL in various tissues of flax stem revealed that LusRGLs belong to distinct phylogenetic clades, which correspond to two co-expression groups. One of these groups comprised LusRGL6-A and LusRGL6-B genes and was specifically upregulated in flax fibers during deposition of the tertiary cell wall, which has complex RG-I as a key noncellulosic component. The results of homology modeling and docking demonstrated that the topology of the LusRGL6-A catalytic site allowed binding to the RG-I ligand. These findings lead us to suggest the presence of RGL activity in planta and the involvement of special isoforms of RGLs in the modification of RG-I of the tertiary cell wall in plant fibers.

Temporal biosynthesis of flavone constituents in flax growth stages

Previous studies showed that chalcone synthase (chs) silencing in flax (Linum usitatisimum) induces a signal transduction cascade that leads to extensive modification of plant metabolism. Result presented in the current study, performed on field grown flax plants - (across the whole vegetation period) demonstrates that, in addition to its role in tannin and lignin biosynthesis, the chs gene also participates in the regulation of flavone biosynthesis during plant growth. Apigenin and luteolin glycosides constitute the flavones, the major group of flavonoids in flax. Alterations in their levels correlate with plant growth, peaking at the flower initiation stage. Suppression of chs gene expression causes significant changes in the ratio of flavone constituents at the early stage of flax growth. A significant correlation between flavonoid 3'-hydroxylase (F3'H) gene expression and accumulation of luteolin glycosides has been found, indicating that flavone biosynthesis during flax growth and development is regulated by temporal expression of this gene. The lack of such a correlation between the flavone synthase (FNS) gene and flavone accumulation in the course of plant growth suggests that the main route of flavone biosynthesis is mediated by eriodictyol. This is the first report indicating the ratio of flavone constituents as a potent marker of flax growth stages and temporal expression of F3'H, the key gene of their biosynthesis.

Influence of spray drying encapsulation on the retention of antioxidant properties and microstructure of flaxseed protein hydrolysates

In this research, bioactive peptides produced from flaxseed protein by alcalase, pancreatin, trypsin and pepsin, were encapsulated by spray drying. After analysis of amino acid composition and antioxidant properties of hydrolysates, the effect of spray-drying encapsulation via different maltodextrin (MD) to hydrolysate ratios (1:1, 2:1 and 3:1 w/w) on the production yield, physicochemical properties, functional activities, chemical structure, and morphology of final powder particles were evaluated. Among the hydrolysates, peptides produced with alcalase had the highest hydrolysis degree (38.2%), hydrophobic amino acids (255 mg/g) and antioxidants (126 mg/g). Among spray-dried samples, the powders obtained by 3:1 w/w ratio (MD: peptide) showed the highest radical scavenging activity for DPPH^- (68.93%), ABTS⁺ (85.62%), hydroxyl (94.97%), nitric oxide (64.03%), reducing power (95.49%), total antioxidant activity (96.68%), and iron (95.31%) and copper (95.49%) chelating activity. Evaluation of chemical structure (FTIR) indicated that hydrolysates were coated and dispersed within maltodextrin matrix. SEM images showed the effect of different carrier ratios on the production of irregular and shrunk particles with different sizes and matrix-type structures.

RNAi-mediated silencing of pinoresinol lariciresinol reductase in Linum album hairy roots alters the phenolic accumulation in response to fungal elicitor

Lignans are diphenolic compounds produced in plants via coupling of two coniferyl alcohol molecules with the aid of a dirigent protein to form pinoresinol (PINO). The latter is reduced via lariciresinol (LARI) to secoisolariciresinol by the bifunctional pinoresinol-lariciresinol reductase (PLR). In this study, we clarified the consequences of altered lignan biosynthesis on amino acids, phenolics compounds and lignin in the hairy roots of Linum album with an ihpRNAi construct to silence PLR gene expression. Down-regulation of PLR-La1 resulted in up to an 8.3 and 3.3-time increased PINO and LARI content respectively, and reduced levels of podophyllotoxin (PTOX) and 6-methoxy podophyllotoxin (6-MPTOX). By Suppression of PLR expression, the metabolites belonging to shikimate and phenylpropanoid pathways are conducted to phenolic compounds and lignin accumulations. Although PINO and LARI were induced in response to fungal elicitor, the accumulation of PTOX and 6-MPTOX did not occur in PLR down-regulated roots. Our result also demonstrated variation in amino acids, phenolic compounds and lignin levels in presence of the fungal elicitation in PLR down regulated-roots. This data assert the accumulation of aryltetralin lignans in interactions with plant pathogens by PLR activity and the importance this enzyme for defense against pathogens in L. album.

Expression of heterologous lycopene β-cyclase gene in flax can cause silencing of its endogenous counterpart by changes in gene-body methylation and in ABA homeostasis mechanism

Previously we described flax plants with expression of Arabidopsis lycopene β-cyclase (lcb) gene in which decreased expression of the endogenous lcb and increased resistance to fungal pathogen was observed. We suggested that co-suppression was responsible for the change. In this study we investigated the molecular basis of the observed effect in detail. We found that methylation changes in the Lulcb gene body might be responsible for repression of the gene. Treatment with azacitidine (DNA methylation inhibitor) confirmed the results. Moreover, we studied how the manipulation of carotenoid biosynthesis pathway increased ABA level in these plants. We suggest that elevated ABA levels may be responsible for the increased resistance of the flax plants to pathogen infection through activation of chitinase (PR gene).

Molecular details of secretory phospholipase A2 from flax (Linum usitatissimum L.) provide insight into its structure and function

Secretory phospholipase A₂ (sPLA₂) are low molecular weight proteins (12-18 kDa) involved in a suite of plant cellular processes imparting growth and development. With myriad roles in physiological and biochemical processes in plants, detailed analysis of sPLA₂ in flax/linseed is meagre. The present work, first in flax, embodies cloning, expression, purification and molecular characterisation of two distinct sPLA₂s (I and II) from flax. PLA₂ activity of the cloned sPLA₂s were biochemically assayed authenticating them as bona fide phospholipase A₂. Physiochemical properties of both the sPLA₂s revealed they are thermostable proteins requiring di-valent cations for optimum activity.While, structural analysis of both the proteins revealed deviations in the amino acid sequence at C- & N-terminal regions; hydropathic study revealed LusPLA₂I as a hydrophobic protein and LusPLA₂II as a hydrophilic protein. Structural analysis of flax sPLA₂s revealed that secondary structure of both the proteins are dominated by α-helix followed by random coils. Modular superimposition of LusPLA₂ isoforms with rice sPLA₂ confirmed monomeric structural preservation among plant phospholipase A₂ and provided insight into structure of folded flax sPLA₂s.

Molecular details of secretory phospholipase A2 from flax (Linum usitatissimum L.) provide insight into its structure and function

Secretory phospholipase A2 (sPLA2) are low molecular weight proteins (12-18 kDa) involved in a suite of plant cellular processes imparting growth and development. With myriad roles in physiological and biochemical processes in plants, detailed analysis of sPLA2 in flax/linseed is meagre. The present work, first in flax, embodies cloning, expression, purification and molecular characterisation of two distinct sPLA2s (I and II) from flax. PLA2 activity of the cloned sPLA2s were biochemically assayed authenticating them as bona fide phospholipase A2. Physiochemical properties of both the sPLA2s revealed they are thermostable proteins requiring di-valent cations for optimum activity.While, structural analysis of both the proteins revealed deviations in the amino acid sequence at C- & N-terminal regions; hydropathic study revealed LusPLA2I as a hydrophobic protein and LusPLA2II as a hydrophilic protein. Structural analysis of flax sPLA2s revealed that secondary structure of both the proteins are dominated by α-helix followed by random coils. Modular superimposition of LusPLA2 isoforms with rice sPLA2 confirmed monomeric structural preservation among plant phospholipase A2 and provided insight into structure of folded flax sPLA2s.

Functional characterization of the pinoresinol-lariciresinol reductase-2 gene reveals its roles in yatein biosynthesis and flax defense response

MAIN CONCLUSION

This study provides new insights into the biosynthesis regulation and in planta function of the lignan yatein in flax leaves. Pinoresinol-lariciresinol reductases (PLR) catalyze the conversion of pinoresinol into secoisolariciresinol (SECO) in lignan biosynthesis. Several lignans are accumulated in high concentrations, such as SECO accumulated as secoisolariciresinol diglucoside (SDG) in seeds and yatein in aerial parts, in the flax plant (Linum usitatissimum L.) from which two PLR enzymes of opposite enantioselectivity have been isolated. While LuPLR1 catalyzes the biosynthesis of (+)-SECO leading to (+)-SDG in seeds, the role(s) of the second PLR (LuPLR2) is not completely elucidated. This study provides new insights into the in planta regulation and function of the lignan yatein in flax leaves: its biosynthesis relies on a different PLR with opposite stereospecificity but also on a distinct expression regulation. RNAi technology provided evidence for the in vivo involvement of the LuPLR2 gene in the biosynthesis of (-)-yatein accumulated in flax leaves. LuPLR2 expression in different tissues and in response to stress was studied by RT-qPCR and promoter-reporter transgenesis showing that the spatio-temporal expression of the LuPLR2 gene in leaves perfectly matches the (-)-yatein accumulation and that LuPLR2 expression and yatein production are increased by methyl jasmonate and wounding. A promoter deletion approach yielded putative regulatory elements. This expression pattern in relation to a possible role for this lignan in flax defense is discussed.

Spatial regulation of monolignol biosynthesis and laccase genes control developmental and stress-related lignin in flax

BACKGROUND

Bast fibres are characterized by very thick secondary cell walls containing high amounts of cellulose and low lignin contents in contrast to the heavily lignified cell walls typically found in the xylem tissues. To improve the quality of the fiber-based products in the future, a thorough understanding of the main cell wall polymer biosynthetic pathways is required. In this study we have carried out a characterization of the genes involved in lignin biosynthesis in flax along with some of their regulation mechanisms.

RESULTS

We have first identified the members of the phenylpropanoid gene families through a combination of in silico approaches. The more specific lignin genes were further characterized by high throughput transcriptomic approaches in different organs and physiological conditions and their cell/tissue expression was localized in the stems, roots and leaves. Laccases play an important role in the polymerization of monolignols. This multigenic family was determined and a miRNA was identified to play a role in the posttranscriptional regulation by cleaving the transcripts of some specific genes shown to be expressed in lignified tissues. In situ hybridization also showed that the miRNA precursor was expressed in the young xylem cells located near the vascular cambium. The results obtained in this work also allowed us to determine that most of the genes involved in lignin biosynthesis are included in a unique co-expression cluster and that MYB transcription factors are potentially good candidates for regulating these genes.

CONCLUSIONS

Target engineering of cell walls to improve plant product quality requires good knowledge of the genes responsible for the production of the main polymers. For bast fiber plants such as flax, it is important to target the correct genes from the beginning since the difficulty to produce transgenic material does not make possible to test a large number of genes. Our work determined which of these genes could be potentially modified and showed that it was possible to target different regulatory pathways to modify lignification.

IMPACT OF FABRICS FROM TRANSGENIC FLAX PLANT ON HUMAN DERMAL FIBROBLASTS IN VITRO PROLIFERATION

Previously it was documented that transgenic flax plants, which contained an increased level of polyphenolic compounds, significantly improved healing of skin wounds lesions. In order to recognize mechanisms of beneficial action of transgenic flax fabrics on wound healing, in the present study the impact of flax fabric pieces/cuts from three types of transgenic flax on normal human dermal fibroblasts primary culture (NHDF) was investigated. NHDF cell cultures were exposed for 48 h to specific area of flax fabric cuts, made from M50, B 14 and M50+B14 (intertwined fibers of M and B), or parallely, extracts from fibers of the tested flax materials to cell culture medium. Cultures were inspected for cell viability, proliferation, cell cycle changes and for their resistance to oxidative stress (consecutive addition of H₂,O₂, to harvested cell cultures). None of the tested flax fabrics were cytotoxic to fibroblast cultures and also did not increase significantly a frequency of apoptotic cells in cultures. In the comet assay, the tested flax fabrics revealed significant protective effect on DNA damage ciused by addition of H₂0₂ to the cultures at the end of incubation time. Fabrics from transgenic flax significantly enhanced fibroblasts proliferation in vitro estimated with the SRB test. Flow cytometric analysis revealed higher frequency of cells in the S phase, in the presence of transgenic flax fabrics. Fabrics from B14 and M50+B14 flax are the most potent activators of NHDF cells in applied in vityo tests, hence they could be recommended for elaboration of new type bandage, able to improve skin wound healing.

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.

Sequence characterization and in silico structure prediction of fatty acid desaturases in linseed varieties with differential fatty acid composition

BACKGROUND

Linseed is the richest agricultural source of α-linolenic acid (ALA), an ω-3 fatty acid (FA) that offers several nutritional benefits. In the present study, sequence characterization of six desaturase genes (SAD1, SAD2, FAD2, FAD2-2, FAD3A and FAD3B) and 3D structure prediction of their proteins from ten Indian linseed varieties differing in ALA content were performed to determine whether the nucleotide and amino acid (AA) sequence variants have any functional implications in differential accumulation of ALA or other FAs in linseed.

RESULTS

The SAD and FAD2 genes exhibited few sequence variations among the ten varieties, forming only one or two protein isoforms. In contrast, the FAD3A and FAD3B genes showed more sequence variations and three or four protein isoforms. Interestingly, the two high-ALA varieties NL260 and Padmini had the same FAD3B nucleotide and protein isoforms, which differed from all other varieties. Surprisingly, no AA changes altered the 3D structures of the desaturase proteins.

CONCLUSION

Several nucleotide and AA sequence variations in desaturase genes were observed; however, they did not alter the 3D structure of any desaturase protein and were not correlated with FA levels among the ten linseed varieties, which had different ALA contents. This suggests a complex regulatory process of biosynthesis of FAs in linseed. © 2016 Society of Chemical Industry.

Functional analyses of cellulose synthase genes in flax (Linum usitatissimum) by virus-induced gene silencing

Flax (Linum usitatissimum) bast fibres are located in the stem cortex where they play an important role in mechanical support. They contain high amounts of cellulose and so are used for linen textiles and in the composite industry. In this study, we screened the annotated flax genome and identified 14 distinct cellulose synthase (CESA) genes using orthologous sequences previously identified. Transcriptomics of 'primary cell wall' and 'secondary cell wall' flax CESA genes showed that some were preferentially expressed in different organs and stem tissues providing clues as to their biological role(s) in planta. The development for the first time in flax of a virus-induced gene silencing (VIGS) approach was used to functionally evaluate the biological role of different CESA genes in stem tissues. Quantification of transcript accumulation showed that in many cases, silencing not only affected targeted CESA clades, but also had an impact on other CESA genes. Whatever the targeted clade, inactivation by VIGS affected plant growth. In contrast, only clade 1- and clade 6-targeted plants showed modifications in outer-stem tissue organization and secondary cell wall formation. In these plants, bast fibre number and structure were severely impacted, suggesting that the targeted genes may play an important role in the establishment of the fibre cell wall. Our results provide new fundamental information about cellulose biosynthesis in flax that should facilitate future plant improvement/engineering.

Kinetics of glucosylated and non-glucosylated aryltetralin lignans in Linum hairy root cultures

Due to their pronounced cytotoxic activity, a number of aryltetralin lignans (ATLs), such as podophyllotoxin (PTOX), are used as antitumor compounds. The production of such molecules from entire plants or plant cell-tissue-organ cultures is thus of interest to the pharmaceutical industry. Hairy root cultures constitute a good tool not only for phytochemical production but also for investigating plant secondary metabolism. This work reports on the growth and ATL biosynthesis in two hairy root cultures of Linum album Kotschy ex Boiss. and Linum flavum. The kinetics of accumulation of the intermediates of MPTOX biosynthesis and of their glucosylated forms are described over a 21-day period of growth. An accumulation of non-glucosylated forms of the ATLs during the exponential phase of the cultures is followed by an accumulation of the glucosylated forms during the stationary phase. Our results show a strong coordination of the biosynthetic paths derived from deoxypodophyllotoxin via deoxypodophyllotoxin 6-hydroxylase and deoxypodophyllotoxin 7-hydroxylase, and a coordinated glucosylation of podophyllotoxin, methoxypodophyllotoxin, and 5'-demethoxymethoxypodophyllotoxin. Furthermore, our results suggest an important role of β-peltatin-6-glucoside formation in the control of ATL accumulation in Linum hairy root cultures.

Development of high oleic oil crop platform in flax through RNAi-mediated multiple FAD2 gene silencing

Simultaneous gene silencing of both FAD2 genes in high linoleic acid flax leads to high level of oleic acid, which is stable across multiple generations. High oleic oil is one of the preferred traits in oil crop engineering due to its stability and multiple applications as an industrial feedstock. Flax possesses two isoforms of FAD2 enzymes that desaturate monounsaturated oleic acid to polyunsaturated linoleic acid. These two enzymes are encoded by two FAD2 genes. By simultaneous gene silencing both FAD2 genes in high linoleic acid flax, Linola, high level of oleic acid up to 80% was achieved in 69 silencing lines. The high oleic trait was stable across multiple generations with oleic acid reaching up to 77% in homozygote T3 progeny. The RNAi-mediated gene-silencing approach generated high oleic linseed oil, as well as a high oleic platform that can be exploited for further fatty acid engineering.

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.

Ectopic lignification in the flax lignified bast fiber1 mutant stem is associated with tissue-specific modifications in gene expression and cell wall composition

Histochemical screening of a flax ethyl methanesulfonate population led to the identification of 93 independent M2 mutant families showing ectopic lignification in the secondary cell wall of stem bast fibers. We named this core collection the Linum usitatissimum (flax) lbf mutants for lignified bast fibers and believe that this population represents a novel biological resource for investigating how bast fiber plants regulate lignin biosynthesis. As a proof of concept, we characterized the lbf1 mutant and showed that the lignin content increased by 350% in outer stem tissues containing bast fibers but was unchanged in inner stem tissues containing xylem. Chemical and NMR analyses indicated that bast fiber ectopic lignin was highly condensed and rich in G-units. Liquid chromatography-mass spectrometry profiling showed large modifications in the oligolignol pool of lbf1 inner- and outer-stem tissues that could be related to ectopic lignification. Immunological and chemical analyses revealed that lbf1 mutants also showed changes to other cell wall polymers. Whole-genome transcriptomics suggested that ectopic lignification of flax bast fibers could be caused by increased transcript accumulation of (1) the cinnamoyl-CoA reductase, cinnamyl alcohol dehydrogenase, and caffeic acid O-methyltransferase monolignol biosynthesis genes, (2) several lignin-associated peroxidase genes, and (3) genes coding for respiratory burst oxidase homolog NADPH-oxidases necessary to increase H2O2 supply.

Oligonucleotide treatment causes flax β-glucanase up-regulation via changes in gene-body methylation

BACKGROUND

Nowadays, the challenge for biotechnology is to develop tools for agriculture and industry to provide plants characterized by productivity and quality that will satisfy the growing demand for different kinds of natural products. To meet the challenge, the generation and application of genetically modified plants is justified. However, the strong social resistance to genetically modified organisms and restrictive regulations in European Union countries necessitated the development of a new technology for new plant types generation which uses the knowledge resulting from analysis of genetically modified plants to generate favourably altered plants while omitting the introduction of heterologous genes to their genome. Four-year experiments led to the development of a technology inducing heritable epigenetic gene activation without transgenesis.

RESULTS

The method comprises the induction of changes in methylation/demethylation of the endogenous gene by the plant's treatment with short oligodeoxynucleotides antisense to the coding region. In vitro cultured plants and F3 generation flax plants overproducing the β-1,3-glucanase gene (EMO-βGlu flax) were characterized by up-regulation of β-glucanase and chitinase genes, decreases in the methylation of CCGG sequences in the β-glucanase gene and in total DNA methylation and, more importantly, reasonable resistance against Fusarium infection. In addition, EMO-βGlu flax obtained by this technology showed similar features as those obtained by genetic engineering.

CONCLUSION

To our best knowledge, this is the first report on plant gene activation by treatment with oligodeoxynucleotides homologous to the coding region of the gene. Apart from the evident effectiveness, the most important issue is that the EMO method allows generation of favourably altered plants, whose cultivation makes the plant producer independent from the complicated procedure of obtaining an agreement on GMO release into the environment and whose products might be more easily introduced to the global market.

Genetically modified flax expressing NAP-SsGT1 transgene: examination of anti-inflammatory action

The aim of the work was to define the influence of dietary supplementation with GM (genetically modified) GT#4 flaxseed cake enriched in polyphenols on inflammation development in mice liver. Mice were given ad libitum isoprotein diets: (1) standard diet; (2) high-fat diet rich in lard, high-fat diet enriched with 30% of (3) isogenic flax Linola seed cake; and (4) GM GT#4 flaxseed cake; for 96 days. Administration of transgenic and isogenic seed cake lowered body weight gain, of transgenic to the standard diet level. Serum total antioxidant status was statistically significantly improved in GT#4 flaxseed cake group and did not differ from Linola. Serum thiobarbituric acid reactive substances, lipid profile and the liver concentration of pro-inflammatory cytokine tumor necrosis factor-α were ameliorated by GM and isogenic flaxseed cake consumption. The level of pro-inflammatory cytokine interferon-γ did not differ between mice obtaining GM GT#4 and non-GM flaxseed cakes. The C-reactive protein concentration was reduced in animals fed GT#4 flaxseed cake and did not differ from those fed non-GM flaxseed cake-based diet. Similarly, the liver structure of mice consuming diets enriched in flaxseed cake was improved. Dietetic enrichment with GM GT#4 and non-GM flaxseed cakes may be a promising solution for health problems resulting from improper diet.

RNAi-mediated pinoresinol lariciresinol reductase gene silencing in flax (Linum usitatissimum L.) seed coat: consequences on lignans and neolignans accumulation

RNAi technology was applied to down regulate LuPLR1 gene expression in flax (Linum usitatissimum L.) seeds. This gene encodes a pinoresinol lariciresinol reductase responsible for the synthesis of (+)-secoisolariciresinol diglucoside (SDG), the major lignan accumulated in the seed coat. If flax lignans biological properties and health benefits are well documented their roles in planta remain unclear. This loss of function strategy was developed to better understand the implication of the PLR1 enzyme in the lignan biosynthetic pathway and to provide new insights on the functions of these compounds. RNAi plants generated exhibited LuPLR1 gene silencing as demonstrated by quantitative RT-PCR experiments and the failed to accumulate SDG. The accumulation of pinoresinol the substrate of the PLR1 enzyme under its diglucosylated form (PDG) was increased in transgenic seeds but did not compensate the overall loss of SDG. The monolignol flux was also deviated through the synthesis of 8-5' linked neolignans dehydrodiconiferyl alcohol glucoside (DCG) and dihydro-dehydrodiconiferyl alcohol glucoside (DDCG) which were observed for the first time in flax seeds.

Chitinase-like (CTL) and cellulose synthase (CESA) gene expression in gelatinous-type cellulosic walls of flax (Linum usitatissimum L.) bast fibers

Plant chitinases (EC 3.2.1.14) and chitinase-like (CTL) proteins have diverse functions including cell wall biosynthesis and disease resistance. We analyzed the expression of 34 chitinase and chitinase-like genes of flax (collectively referred to as LusCTLs), belonging to glycoside hydrolase family 19 (GH19). Analysis of the transcript expression patterns of LusCTLs in the stem and other tissues identified three transcripts (LusCTL19, LusCTL20, LusCTL21) that were highly enriched in developing bast fibers, which form cellulose-rich gelatinous-type cell walls. The same three genes had low relative expression in tissues with primary cell walls and in xylem, which forms a xylan type of secondary cell wall. Phylogenetic analysis of the LusCTLs identified a flax-specific sub-group that was not represented in any of other genomes queried. To provide further context for the gene expression analysis, we also conducted phylogenetic and expression analysis of the cellulose synthase (CESA) family genes of flax, and found that expression of secondary wall-type LusCESAs (LusCESA4, LusCESA7 and LusCESA8) was correlated with the expression of two LusCTLs (LusCTL1, LusCTL2) that were the most highly enriched in xylem. The expression of LusCTL19, LusCTL20, and LusCTL21 was not correlated with that of any CESA subgroup. These results defined a distinct type of CTLs that may have novel functions specific to the development of the gelatinous (G-type) cellulosic walls.

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.

Manipulating cinnamyl alcohol dehydrogenase (CAD) expression in flax affects fibre composition and properties

BACKGROUND

In recent decades cultivation of flax and its application have dramatically decreased. One of the reasons for this is unpredictable quality and properties of flax fibre, because they depend on environmental factors, retting duration and growing conditions. These factors have contribution to the fibre composition, which consists of cellulose, hemicelluloses, lignin and pectin. By far, it is largely established that in flax, lignin reduces an accessibility of enzymes either to pectin, hemicelluloses or cellulose (during retting or in biofuel synthesis and paper production).Therefore, in this study we evaluated composition and properties of flax fibre from plants with silenced CAD (cinnamyl alcohol dehydrogenase) gene, which is key in the lignin biosynthesis. There is evidence that CAD is a useful tool to improve lignin digestibility and/or to lower the lignin levels in plants.

RESULTS

Two studied lines responded differentially to the introduced modification due to the efficiency of the CAD silencing. Phylogenetic analysis revealed that flax CAD belongs to the "bona-fide" CAD family. CAD down-regulation had an effect in the reduced lignin amount in the flax fibre cell wall and as FT-IR results suggests, disturbed lignin composition and structure. Moreover introduced modification activated a compensatory mechanism which was manifested in the accumulation of cellulose and/or pectin. These changes had putative correlation with observed improved fiber's tensile strength. Moreover, CAD down-regulation did not disturb at all or has only slight effect on flax plants' development in vivo, however, the resistance against flax major pathogen Fusarium oxysporum decreased slightly. The modification positively affected fibre possessing; it resulted in more uniform retting.

CONCLUSION

The major finding of our paper is that the modification targeted directly to block lignin synthesis caused not only reduced lignin level in fibre, but also affected amount and organization of cellulose and pectin. However, to conclude that all observed changes are trustworthy and correlated exclusively to CAD repression, further analysis of the modified plants genome is necessary. Secondly, this is one of the first studies on the crop from the low-lignin plants from the field trail which demonstrates that such plants could be successfully cultivated in a field.

[Cellulose synthase genes that control the fiber formation of flax (Linum usitatissimum L.)]

Four cellulose synthase genes were identified by analysis of their class-specific regions (CSRII) in plants of fiber flax during the "rapid growth" stage. These genes were designated as LusCesA1, LusCesA4, LusCesA7 and LusCesA9. LusCesA4, LusCesA7, and LusCesA9 genes were expressed in the stem; LusCesA1 and LusCesA4 genes were expressed in the apex part of plants, and the LusCesA4 gene was expressed in the leaves of fiber flax. The expression of the LusCesA7 and LusCesA9 genes was specific to the stems of fiber flax. These genes may influence the quality of the flax fiber.

Crystallization and preliminary X-ray diffraction analysis of the flax cytokinin oxidase LuCKX1.1

The plant hormones cytokinins play a central role in regulating cell division and developmental events. Cytokinin oxidase regulates the levels of these plant hormones by catalyzing their irreversible oxidation, which contributes to the regulation of various morpho-physiological processes controlled by cytokinins. In this study, the crystallization and preliminary X-ray diffraction analysis of the flax cytokinin oxidase LuCKX1.1 are reported. Plate-like crystals of LuCKX1.1 were obtained using PEG 3350 as a precipitant and diffracted X-rays to 1.78 Å resolution. The protein crystals have the symmetry of space group C2 and are most likely to contain two molecules per asymmetric unit.

Genetic variation of six desaturase genes in flax and their impact on fatty acid composition

Flax (Linum usitatissimum L.) is one of the richest plant sources of omega-3 fatty acids praised for their health benefits. In this study, the extent of the genetic variability of genes encoding stearoyl-ACP desaturase (SAD), and fatty acid desaturase 2 (FAD2) and 3 (FAD3) was determined by sequencing the six paralogous genes from 120 flax accessions representing a broad range of germplasm including some EMS mutant lines. A total of 6 alleles for sad1 and sad2, 21 for fad2a, 5 for fad2b, 15 for fad3a and 18 for fad3b were identified. Deduced amino acid sequences of the alleles predicted 4, 2, 3, 4, 6 and 7 isoforms, respectively. Allele frequencies varied greatly across genes. Fad3a, with 110 SNPs and 19 indels, and fad3b, with 50 SNPs and 5 indels, showed the highest levels of genetic variations. While most of the SNPs and all the indels were silent mutations, both genes carried nonsense SNP mutations resulting in premature stop codons, a feature not observed in sad and fad2 genes. Some alleles and isoforms discovered in induced mutant lines were absent in the natural germplasm. Correlation of these genotypic data with fatty acid composition data of 120 flax accessions phenotyped in six field experiments revealed statistically significant effects of some of the SAD and FAD isoforms on fatty acid composition, oil content and iodine value. The novel allelic variants and isoforms identified for the six desaturases will be a resource for the development of oilseed flax with unique and useful fatty acid profiles.

Genetic variation of six desaturase genes in flax and their impact on fatty acid composition

Flax (Linum usitatissimum L.) is one of the richest plant sources of omega-3 fatty acids praised for their health benefits. In this study, the extent of the genetic variability of genes encoding stearoyl-ACP desaturase (SAD), and fatty acid desaturase 2 (FAD2) and 3 (FAD3) was determined by sequencing the six paralogous genes from 120 flax accessions representing a broad range of germplasm including some EMS mutant lines. A total of 6 alleles for sad1 and sad2, 21 for fad2a, 5 for fad2b, 15 for fad3a and 18 for fad3b were identified. Deduced amino acid sequences of the alleles predicted 4, 2, 3, 4, 6 and 7 isoforms, respectively. Allele frequencies varied greatly across genes. Fad3a, with 110 SNPs and 19 indels, and fad3b, with 50 SNPs and 5 indels, showed the highest levels of genetic variations. While most of the SNPs and all the indels were silent mutations, both genes carried nonsense SNP mutations resulting in premature stop codons, a feature not observed in sad and fad2 genes. Some alleles and isoforms discovered in induced mutant lines were absent in the natural germplasm. Correlation of these genotypic data with fatty acid composition data of 120 flax accessions phenotyped in six field experiments revealed statistically significant effects of some of the SAD and FAD isoforms on fatty acid composition, oil content and iodine value. The novel allelic variants and isoforms identified for the six desaturases will be a resource for the development of oilseed flax with unique and useful fatty acid profiles.

Structure-function relationship in the CYP74 family: conversion of divinyl ether synthases into allene oxide synthases by site-directed mutagenesis

Non-classical P450s of CYP74 family control several enzymatic conversions of fatty acid hydroperoxides to bioactive oxylipins in plants, some invertebrates and bacteria. The family includes two dehydrases, namely allene oxide synthase (AOS) and divinyl ether synthase (DES), and two isomerases, hydroperoxide lyase (HPL) and epoxyalcohol synthase. To study the interconversion of different CYP74 enzymes, we prepared the mutant forms V379F and E292G of tobacco (CYP74D3) and flax (CYP74B16) divinyl ether synthases (DESs), respectively. In contrast to the wild type (WT) enzymes, both mutant forms lacked DES activity. Instead, they produced the typical AOS products, α-ketols and (in the case of the flax DES mutant) 12-oxo-10,15-phytodienoic acid. This is the first demonstration of DES into AOS conversions caused by single point mutations.

Identification and characterization of cis-acting elements involved in the regulation of ABA- and/or GA-mediated LuPLR1 gene expression and lignan biosynthesis in flax (Linum usitatissimum L.) cell cultures

Pinoresinol lariciresinol reductase 1, encoded by the LuPLR1 gene in flax (Linum usitatissimum L.), is responsible for the biosynthesis of (+)-secoisolariciresinol, a cancer chemopreventive phytoestrogenic lignan accumulated in high amount in the hull of flaxseed. Our recent studies have demonstrated a key role of abscisic acid (ABA) in the regulation of LuPLR1 gene expression and thus of the (+)-secoisolariciresinol synthesis during the flax seedcoat development. It is well accepted that gibberellins (GA) and ABA play antagonistic roles in the regulation of numerous developmental processes; therefore it is of interest to clarify their respective effects on lignan biosynthesis. Herein, using flax cell suspension cultures, we demonstrate that LuPLR1 gene expression and (+)-secoisolariciresinol synthesis are up-regulated by ABA and down-regulated by GA. The LuPLR1 gene promoter analysis and mutation experiments allow us to identify and characterize two important cis-acting sequences (ABRE and MYB2) required for these regulations. These results imply that a cross-talk between ABA and GA signaling orchestrated by transcription factors is involved in the regulation of lignan biosynthesis. This is particularly evidenced in the case of the ABRE cis-regulatory sequence of LuPLR1 gene promoter that appears to be a common target sequence of GA and ABA signals.

Fibres from flax overproducing β-1,3-glucanase show increased accumulation of pectin and phenolics and thus higher antioxidant capacity

BACKGROUND

Recently, in order to improve the resistance of flax plants to pathogen infection, transgenic flax that overproduces β-1,3-glucanase was created. β-1,3-glucanase is a PR protein that hydrolyses the β-glucans, which are a major component of the cell wall in many groups of fungi. For this study, we used fourth-generation field-cultivated plants of the Fusarium -resistant transgenic line B14 to evaluate how overexpression of the β-1,3-glucanase gene influences the quantity, quality and composition of flax fibres, which are the main product obtained from flax straw.

RESULTS

Overproduction of β-1,3-glucanase did not affect the quantity of the fibre obtained from the flax straw and did not significantly alter the essential mechanical characteristics of the retted fibres. However, changes in the contents of the major components of the cell wall (cellulose, hemicellulose, pectin and lignin) were revealed. Overexpression of the β-1,3-glucanase gene resulted in higher cellulose, hemicellulose and pectin contents and a lower lignin content in the fibres. Increases in the uronic acid content in particular fractions (with the exception of the 1 M KOH-soluble fraction of hemicelluloses) and changes in the sugar composition of the cell wall were detected in the fibres of the transgenic flax when compared to the contents for the control plants. The callose content was lower in the fibres of the transgenic flax. Additionally, the analysis of phenolic compound contents in five fractions of the cell wall revealed important changes, which were reflected in the antioxidant potential of these fractions.

CONCLUSION

Overexpression of the β-1,3-glucanase gene has a significant influence on the biochemical composition of flax fibres. The constitutive overproduction of β-1,3-glucanase causes a decrease in the callose content, and the resulting excess glucose serves as a substrate for the production of other polysaccharides. The monosaccharide excess redirects the phenolic compounds to bind with polysaccharides instead of to partake in lignin synthesis. The mechanical properties of the transgenic fibres are strengthened by their improved biochemical composition, and the increased antioxidant potential of the fibres supports the potential use of transgenic flax fibres for biomedical applications.

Effects of genetic modifications to flax (Linum usitatissimum) on arbuscular mycorrhiza and plant performance

Although arbuscular mycorrhizal fungi (AMF) are known for their positive effect on flax growth, the impact of genetic manipulation in this crop on arbuscular mycorrhiza and plant performance was assessed for the first time. Five types of transgenic flax that were generated to improve fiber quality and resistance to pathogens, through increased levels of either phenylpropanoids (W92.40), glycosyltransferase (GT4, GT5), or PR2 beta-1,3-glucanase (B14) or produce polyhydroxybutyrate (M50), were used. Introduced genetic modifications did not change the degree of mycorrhizal colonization as compared to parent cultivars Linola and Nike. Arbuscules were well developed in each tested transgenic type (except M50). In two lines (W92.40 and B14), a higher abundance of arbuscules was observed when compared to control, untransformed flax plants. However, in some cases (W92.40, GT4, GT5, and B14 Md), the mycorrhizal dependency for biomass production of transgenic plants was slightly lower when compared to the original cultivars. No significant influence of mycorrhiza on the photosynthetic activity of transformed lines was found, but in most cases P concentration in mycorrhizal plants remained higher than in nonmycorrhizal ones. The transformed flax lines meet the demands for better quality of fiber and higher resistance to pathogens, without significantly influencing the interaction with AMF.

Natural hypolignification is associated with extensive oligolignol accumulation in flax stems

Flax (Linum usitatissimum) stems contain cells showing contrasting cell wall structure: lignified in inner stem xylem tissue and hypolignified in outer stem bast fibers. We hypothesized that stem hypolignification should be associated with extensive phenolic accumulation and used metabolomics and transcriptomics to characterize these two tissues. (1)H nuclear magnetic resonance clearly distinguished inner and outer stem tissues and identified different primary and secondary metabolites, including coniferin and p-coumaryl alcohol glucoside. Ultrahigh-performance liquid chromatography-Fourier transform ion cyclotron resonance-mass spectrometry aromatic profiling (lignomics) identified 81 phenolic compounds, of which 65 were identified, to our knowledge, for the first time in flax and 11 for the first time in higher plants. Both aglycone forms and glycosides of monolignols, lignin oligomers, and (neo)lignans were identified in both inner and outer stem tissues, with a preponderance of glycosides in the hypolignified outer stem, indicating the existence of a complex monolignol metabolism. The presence of coniferin-containing secondary metabolites suggested that coniferyl alcohol, in addition to being used in lignin and (neo)lignan formation, was also utilized in a third, partially uncharacterized metabolic pathway. Hypolignification of bast fibers in outer stem tissues was correlated with the low transcript abundance of monolignol biosynthetic genes, laccase genes, and certain peroxidase genes, suggesting that flax hypolignification is transcriptionally regulated. Transcripts of the key lignan genes Pinoresinol-Lariciresinol Reductase and Phenylcoumaran Benzylic Ether Reductase were also highly abundant in flax inner stem tissues. Expression profiling allowed the identification of NAC (NAM, ATAF1/2, CUC2) and MYB transcription factors that are likely involved in regulating both monolignol production and polymerization as well as (neo)lignan production.

Abscisic acid regulates pinoresinol-lariciresinol reductase gene expression and secoisolariciresinol accumulation in developing flax (Linum usitatissimum L.) seeds

Secoisolariciresinol diglucoside (SDG), the main phytoestrogenic lignan of Linum usitatissimum, is accumulated in the seed coat of flax during its development and pinoresinol-lariciresinol reductase (PLR) is a key enzyme in flax for its synthesis. The promoter of LuPLR1, a flax gene encoding a pinoresinol lariciresinol reductase, contains putative regulatory boxes related to transcription activation by abscisic acid (ABA). Gel mobility shift experiments evidenced an interaction of nuclear proteins extracted from immature flax seed coat with a putative cis-acting element involved in ABA response. As ABA regulates a number of physiological events during seed development and maturation we have investigated its involvement in the regulation of this lignan synthesis by different means. ABA and SDG accumulation time courses in the seed as well as LuPLR1 expression were first determined in natural conditions. These results showed that ABA timing and localization of accumulation in the flax seed coat could be correlated with the LuPLR1 gene expression and SDG biosynthesis. Experimental modulations of ABA levels were performed by exogenous application of ABA or fluridone, an inhibitor of ABA synthesis. When submitted to exogenous ABA, immature seeds synthesized 3-times more SDG, whereas synthesis of SDG was reduced in immature seeds treated with fluridone. Similarly, the expression of LuPLR1 gene in the seed coat was up-regulated by exogenous ABA and down-regulated when fluridone was applied. These results demonstrate that SDG biosynthesis in the flax seed coat is positively controlled by ABA through the transcriptional regulation of LuPLR1 gene.

Analysis of LuPME3, a pectin methylesterase from Linum usitatissimum, revealed a variability in PME proteolytic maturation

Pectin methylesterase (PME) catalyses the de-methylesterification of pectin in plant cell walls during cell elongation. (1) Pectins are mainly composed of α(1, 4)-D-galacturonosyl acid units that are synthesised in a methylesterified form in the Golgi apparatus to prevent any interaction with Ca2+ ions during their intracellular transport. (2) The highly methylesterified pectins are then secreted into the apoplasm (3) and subsequently de-methylesterified in muro by PMEs. This can either induce the formation of pectin gels through the Ca2+ crosslinking of neighbouring non-methylesterified chains or create substrates for pectin-degrading enzymes such as polygalacturonases and pectate lyases for the initiation of cell wall loosening. (4) PMEs belong to a large multigene family. Sixty-six PME-related genes are predicted in the Arabidopsis genome. (1) Among them, we have recently shown that AtPME3 (At3g14310), a major basic PME isoform in A. thaliana, is ubiquitously expressed in vascular tissues and play a role in adventitious rooting. (5) In flax (Linum usitatissimum), three genes encoding PMEs have been sequenced so far, including LuPME3, the orthologue of AtPME3. Analysis of the LuPME3 isoform brings new insights into the processing of these proteins.

Interaction between boron and aluminum and their effects on phenolic metabolism of Linum usitatissimum L. roots

Aluminum toxicity is the most important limiting factor for plant growth and development in acidic soils (pH < 5.5). Inhibition of root growth has been considered as a sensitive marker of aluminum toxicity and the best indicator of boron deficiency as well. On the other hand cell wall phenolics (lignin and phenolic acids) have important roles in the reduction of extensibility of cell wall under stress conditions. Therefore, the interaction between boron and aluminum on phenolic compounds and the activity of the enzymes involved in their biosynthesis were investigated in flax seedlings. The seedlings were grown in Hoagland's solution and were treated with 3 B levels (4.5, 45 and 450 μM of H₃BO₃ at deficient, normal, and excess conditions, respectively) and 3 Al levels (0, 50 and 100 μM of AlCl₃.6H₂O). The results showed that Al treatment did not affect B content of roots (B content of Al-treated and non-treated plants were identical), while B treatment, particularly in higher concentrations, decreased Al content of roots compared with the control plants. In addition, the highest B concentration prevented the inhibitory effect of Al on the root length of plants. High concentrations of B also resulted in the decrease of enzyme activities involved in phenolic compounds (i.e., phenylalanine ammonia-lyase, polyphenol oxidase and peroxidase), decrease of lignin content and wall-bound phenols under Al stress, thereby ameliorating Al toxicity. The results suggest that the requirement of flax plants for B under Al stress conditions is higher than that required for growth in normal conditions without Al.

Green leaf divinyl ether synthase: gene detection, molecular cloning and identification of a unique CYP74B subfamily member

Enzymes of the CYP74 family (P450 superfamily) play a key role in the plant lipoxygenase signalling cascade. Recently we detected a pathogen inducible divinyl ether synthase (DES) in flax leaves [Chechetkin, Blufard, Hamberg, Grechkin, 2008]. This prompted us to examine the CYP74 genes in the flax leaf transcriptome. Since the flax genome is not sequenced, we used the PCR approach with degenerate primers related to the conserved domains of selected CYP74 genes; this revealed several CYP74 transcripts in flax leaves. One transcript belongs to the previously described allene oxide synthase (LuAOS, CYP74A, GenBank ID: U00428.1). Another one contains the ORF (1473 bp) of an unknown CYP74B16 gene. Three more nearly identical sequences, including one expressed pseudogene, were also identified. The recombinant CYP74B16 protein expressed in Escherichia coli had 491 amino acid residues and MW of 56 kDa. The preferred substrate of this enzyme is the 13-hydroperoxide of α-linolenic acid, and the reaction product was identified by mass spectrometry, NMR and UV spectroscopy as the divinyl ether (9Z,11E)-12-[(1'Z,3'Z)-hexadienyloxy]-9,11-dodecadienoic acid, (ω5Z)-etherolenic acid. All previously known CYP74B subfamily enzymes are hydroperoxide lyases. The novel flax enzyme CYP74B16 (LuDES) is an unprecedented DES member of the CYP74B subfamily.

Functional and bioinformatic characterisation of sequence variants of Fad3 gene from flax

BACKGROUND

Desaturases are enzymes that drive the multi-step fatty acid biosynthetic pathway. As evident from directed mutagenesis, single base changes in their polypeptide can potentially alter their structure and may result in altered substrate specificity, regioselectivity and even loss of function. The authors have previously isolated several sequence variants of Δ15 desaturase from flax while attempting to clone that gene. The aim of the present study was to analyse these gene variants for their functionality and to predict the tertiary structure of the protein in order to correlate the functional differences with the protein structure.

RESULTS

The variants differed in the rate at which they could convert linoleic acid to α-linolenic acid. The highest conversion rate was 7.03%, while the lowest was 2.39%. The overall shape of the predicted 3D model of the protein is a compact cylinder containing α-helices and β-sheets. The Ramchandran plot of this model revealed that 98.5% of the residues are located in allowed region, which denotes a stable structure.

CONCLUSION

Although the structures of the variants are apparently similar, subtle changes account for variation in their activity. Besides, these substitutions may alter their cross-talk with other proteins and thus differentially influence their specificity, localisation and stability, which in turn may explain the diversity in their function.

Development of cellulosic secondary walls in flax fibers requires beta-galactosidase

Bast (phloem) fibers, tension wood fibers, and other cells with gelatinous-type secondary walls are rich in crystalline cellulose. In developing bast fibers of flax (Linum usitatissimum), a galactan-enriched matrix (Gn-layer) is gradually modified into a mature cellulosic gelatinous-layer (G-layer), which ultimately comprises most of the secondary cell wall. Previous studies have correlated this maturation process with expression of a putative β-galactosidase. Here, we demonstrate that β-galactosidase activity is in fact necessary for the dynamic remodeling of polysaccharides that occurs during normal secondary wall development in flax fibers. We found that developing stems of transgenic (LuBGAL-RNAi) flax with reduced β-galactosidase activity had lower concentrations of free Gal and had significant reductions in the thickness of mature cellulosic G-layers compared with controls. Conversely, Gn-layers, labeled intensively by the galactan-specific LM5 antibody, were greatly expanded in LuBGAL-RNAi transgenic plants. Gross morphology and stem anatomy, including the thickness of bast fiber walls, were otherwise unaffected by silencing of β-galactosidase transcripts. These results demonstrate a specific requirement for β-galactosidase in hydrolysis of galactans during formation of cellulosic G-layers. Transgenic lines with reduced β-galactosidase activity also had biochemical and spectroscopic properties consistent with a reduction in cellulose crystallinity. We further demonstrated that the tensile strength of normal flax stems is dependent on β-galactosidase-mediated development of the phloem fiber G-layer. Thus, the mechanical strength that typifies flax stems is dependent on a thick, cellulosic G-layer, which itself depends on β-galactosidase activity within the precursor Gn-layer. These observations demonstrate a novel role for matrix polysaccharides in cellulose deposition; the relevance of these observations to the development of cell walls in other species is also discussed.

Proteomics analysis of flax grown in Chernobyl area suggests limited effect of contaminated environment on seed proteome

The accident at the Chernobyl Nuclear Power Plant (CNPP) on April 26, 1986 is the most serious nuclear disaster in human history. Surprisingly, while the area proximal to the CNPP remains substantially contaminated with long-lived radioisotopes including (90)Sr and (137)Cs, the local ecosystem has been able to adapt. To evaluate plant adaptation, seeds of a local flax (Linum usitatissimum) variety Kyivskyi were sown in radio-contaminated and control fields of the Chernobyl region. A total protein fraction was isolated from mature seeds, and analyzed using 2-dimensional electrophoresis combined with tandem-mass spectrometry. Interestingly, growth of the plants in the radio-contaminated environment had little effect on proteome and only 35 protein spots differed in abundance (p-value of ≤0.05) out of 720 protein spots that were quantified for seeds harvested from both radio-contaminated and control fields. Of the 35 differentially abundant spots, 28 proteins were identified using state-of-the-art MS(E) method. Based on the observed changes, the proteome of seeds from plants grown in radio-contaminated soil display minor adjustments to multiple signaling pathways.

[Development of specific and degenerated primers to CesA genes encoding flax (Linum usitatissimum L.) cellulose synthase]

Cellulose synthase catalytic subunit genes, CesA, have been discovered in several higher plant species, and it has been shown that the CesA gene family has multiple members. HVR2 fragment of these genes determine the class specificity of the CESA protein and its participation in the primary or secondary cell wall synthesis. The aim of this study was development of specific and degenerated primers to flax CesA gene fragments leading to obtaining the class specific HVR2 region of the gene. Two pairs of specific primers to the certain fragments of CesA-1 and CesA-6 genes and one pair of degenerated primers to HVR2 region of all flax CesA genes were developed basing on comparison of six CesA EST sequences of flax and full cDNA sequences of Arabidopsis, poplar, maize and cotton plants, obtained from GenBank. After amplification of flax cDNA, the bands of expected size were detected (201 and 300 b.p. for the CesA-1 and CesA-6, and 600 b.p. for the HVR2 region of CesA respectively). The developed markers can be used for cloning and sequencing of flax CesA genes, identifying their number in flax genome, tissue and stage specificity.

Pinoresinol-lariciresinol reductases with opposite enantiospecificity determine the enantiomeric composition of lignans in the different organs of Linum usitatissimum L

Lignans in higher plants represent an ideal class of natural products to be investigated for the origin of stereochemical diversity since chiral lignans occur in pure enantiomeric form as well as in enantiomeric mixtures. Seeds of Linum usitatissimum contain 8S, 8'S-(+)- and 8R, 8'R-(-)-secoisolariciresinol [SS-(+)- and RR-(-)-secoisolariciresinol, respectively] as diglucosides (SS- and RR-secoisolariciresinol diglucosides) whereas aerial parts of flowering L. usitatissimum accumulate only lignans derived from RR-(-)-secoisolariciresinol. Pinoresinol-lariciresinol reductase (PLR) catalyzes two early steps in lignan biosynthesis. Up to now, only a cDNA encoding a PLR ( PLR-LU1) which is enantiospecific for the conversion of 8S, 8'S-(-)-pinoresinol (SS-pinoresinol) via 8S, 8'S-(-)-lariciresinol (SS-lariciresinol) to SS-(+)-secoisolariciresinol was cloned. Here we present the cloning of a cDNA encoding a RR-pinoresinol-RR-lariciresinol reductase ( PLR-LU2) from the leaves of L. usitatissimum which converts only RR-pinoresinol to RR-secoisolariciresinol. In leaves and stems of L. usitatissimum accumulating the 8R, 8'R-enantiomers of lignans, only PLR-LU2 was transcriptionally active. Both PLR-LU1 and PLR-LU2 transcripts were observed in seeds and contribute to the synthesis of SS- and RR-secoisolariciresinol, respectively. Thus, the enantiomeric composition of lignans in the organs of L. usitatissimum appears to be determined by the relative action of two PLRs with opposite enantiospecificities rather than by a single enzyme of low enantiospecificity.

Temporal regulation of cell-wall pectin methylesterase and peroxidase isoforms in cadmium-treated flax hypocotyl

BACKGROUND AND AIMS

In hypocotyls of flax (Linum usitatissimum) cadmium-induced reorientation of growth (i.e. an increase in expansion and a decrease in elongation) coincides with marked changes in the methylesterification and cross-linking of homogalacturonans within various cell-wall (CW) domains. The aim of the present study was to examine the involvement of pectin methylesterase (PME) and peroxidase (PER) in this cadmium-induced CW remodelling.

METHODS

CW proteins were extracted from hypocotyls of 10- and 18-d-old flax that had been treated or not treated with 0.5 mm Cd(NO(3))(2). PME and PER expression within these extracts was detected by LC/MS, by isoelectric focusing and enzyme activity assays. Transcript expression by RT-PCR of known flax PME and PER genes was also measured in corresponding samples.

KEY RESULTS

In cadmium-treated seedlings, PME activity increased as compared with controls, particularly at day 10. The increased activity of PME was accompanied by increased abundance of both a basic protein isoform (B2) and a particular transcript (Lupme5). In contrast, induction of PER activity by cadmium was highest at day 18. Among the four reported PER genes, Flxper1 and 3 increased in abundance in the presence of cadmium at day 18.

CONCLUSIONS

The temporal regulation of Lupme and Flxper genes and of their respective enzyme activities fits the previously reported cadmium-induced structural changes of homogalacturonans within the CWs. After PME-catalysed de-esterification of homogalacturonans, their cross-linking would depend on the activity of PERs interacting with calcium-dimerized blocks and reinforce the cell cohesion during the cadmium-induced swelling.

Identification of a potential bottleneck in branched chain fatty acid incorporation into triacylglycerol for lipid biosynthesis in agronomic plants

In plant, unusual fatty acids are produced by a limited number of species. The industrial benefits of these unusual structures have led several groups to study their production in transgenic plants. Their research results led to very modest accumulation in seeds which was largely due to a limited knowledge of the lipid metabolism and fatty acid transfer in plants. More specifically we need to better understand the substrate specificity and selectivity of acyltransferases which are required for the incorporation of these unusual fatty acids into storage triacylglycerols. In our studies we have compared the incorporation of [(14)C] Oleoyl-CoA and Branched Chain Acyls-CoA into [(3)H] LPA-C18:1 by the Lysophosphatidic acid Acyltransferase (LPAAT) from developing seeds of agronomic plants (flax (Linum usitatissimum) and rape (Brassica napus)) and from a plant capable of producing high amounts of hydroxy fatty acids (castor bean (Ricinus communis)). Our assays demonstrate that LPAATs of the three studied species (1) incorporated preferentially oleyl-CoA, (2) could incorporate cyclopropane acyl-CoA when added alone as a substrate, however very weakly for rapeseed and castor bean seeds, (3) presented a low capacity to incorporate methyl branched acyl-CoA when added alone as a substrate (4) weakly incorporated cyclopropane acyl-CoA and was unable to incorporate methyl branched acyl-CoA when presented with an equimolar mix of oleyl-CoA and branched chain acyl-CoA. In all cases, the LPAAT had a low affinity for branched chain acyl-CoAs. The results show that LPAAT activity from agronomic plants constitutes a bottleneck for the incorporation of branched Chain acyl-CoA into PA.

Caffeoyl coenzyme A O-methyltransferase down-regulation is associated with modifications in lignin and cell-wall architecture in flax secondary xylem

Caffeoyl coenzyme A O-methyltransferase (CCoAOMT, EC 2.1.1.104) down-regulated-flax (Linum usitatissimum) plants were generated using an antisense strategy and functionally characterized. Chemical analyses (acetyl bromide and thioacidolysis) revealed that the lignin quantity was reduced and that the Syringyl/Guaïacyl (S/G) lignin monomer ratio was modified in the non-condensed lignin fraction of two independent down-regulated lines. These modifications were associated with altered xylem organization (both lines), reduced cell-wall thickness (one line) and the appearance of an irregular xylem (irx) phenotype (both lines). In addition UV microspectroscopy also indicated that CCoAOMT down-regulation induced changes in xylem cell-wall structure and the lignin fractions. Microscopic examination also suggested that CCoAOMT down-regulation could influence individual xylem cell size and identity. As a first step towards investigating the cellular mechanisms responsible for the unusual structure of flax lignin (G-rich, condensed), recombinant flax CCoAOMT protein was produced and its affinity for different potential substrates evaluated. Results indicated that the preferred substrate was caffeoyl coenzyme A, followed by 5-hydroxyconiferaldehyde suggesting that flax CCoAOMT possesses a small, but probably significant 5' methylating activity, in addition to a more usual 3' methylating activity.

Hinokinin biosynthesis in Linum corymbulosum Reichenb

Due to their peculiar stereochemistry and numerous biological activities, lignans are of widespread interest. As only a few biosynthetic steps have been clarified to date, we aimed to further resolve the molecular basis of lignan biosynthesis. To this end, we first established that the biologically active lignan (-)-hinokinin could be isolated from in vitro cultures of Linum corymbulosum. Two hypothetical pathways were outlined for the biosynthesis of (-)-hinokinin. In both pathways, (+)-pinoresinol serves as the primary substrate. In the first pathway, pinoresinol is reduced via lariciresinol to secoisolariciresinol by a pinoresinol-lariciresinol reductase, and methylenedioxy bridges are formed later. In the second pathway, pinoresinol itself is the substrate for formation of the methylenedioxy bridges, resulting in consecutive production of piperitol and sesamin. To determine which of the proposed hypothetical pathways acts in vivo, we first isolated several cDNAs encoding one pinoresinol-lariciresinol reductase (PLR-Lc1), two phenylcoumaran benzylic ether reductases (PCBER-Lc1 and PCBER-Lc2), and two PCBER-like proteins from a cDNA library of L. corymbulosum. PLR-Lc1 was found to be enantiospecific for the conversion of (+)-pinoresinol to (-)-secoisolariciresinol, which can be further converted to give (-)-hinokinin. Hairy root lines with significantly reduced expression levels of the plr-Lc1 gene were established using RNAi technology. Hinokinin accumulation was reduced to non-detectable levels in these lines. Our results strongly indicate that PLR-Lc1 participates in (-)-hinokinin biosynthesis in L. corymbulosum by the first of the two hypothetical pathways via (-)-secoisolariciresinol.

A lipoxygenase-divinyl ether synthase pathway in flax (Linum usitatissimum L.) leaves

Incubation of linoleic acid with an enzyme preparation from leaves of flax (Linum usitatissimum L.) led to the formation of a divinyl ether fatty acid, i.e. (9Z,11E,1'Z)-12-(1'-hexenyloxy)-9,11-dodecadienoic [(omega5Z)-etheroleic] acid, as well as smaller amounts of 13-hydroxy-9(Z),11(E)-octadecadienoic acid. The 13-hydroperoxide of linoleic acid afforded the same set of products, whereas incubations of alpha-linolenic acid and its 13-hydroperoxide afforded the divinyl ether (9Z,11E,1'Z,3'Z)-12-(1',3'-hexadienyloxy)-9,11-dodecadienoic [(omega5Z)-etherolenic] as the main product. Identification of both divinyl ethers was substantiated by their UV, mass-, (1)H NMR and COSY spectral data. In addition to the 13-lipoxygenase and divinyl ether synthase activities demonstrated by these results, flax leaves also contained allene oxide synthase activity as judged by the presence of endogenously formed (15Z)-cis-12-oxo-10,15-phytodienoic acid in all incubations.

A possible role of prolyl oligopeptidase during Linum usitatissimum (flax) seed development

Involvement of prolyl oligopeptidases (POPs) in the control of several mammalian peptide hormone signalling pathways has been studied extensively in recent years. POPs are ubiquitous enzymes, but little attention has been paid to understanding their function in plants. Using a cDNA-AFLP approach, two flax (Linum usitatissimum) POP ESTs were identified as being specifically expressed in the early stages of flax seed development. This specific expression was confirmed using real time RT-PCR and in situ hybridisation approaches. Seed expression of Arabidopsis POP genes was measured and showed no specificity. Comparison between results obtained with flax and Arabidopsis is discussed in order to address a hypothetic function for POPs during seed formation. These results provide the first insights into POP gene expression and hypothetical function in plants.

A flax fibre proteome: identification of proteins enriched in bast fibres

BACKGROUND

Bast fibres from the phloem tissues of flax are scientifically interesting and economically useful due in part to a dynamic system of secondary cell wall deposition. To better understand the molecular mechanisms underlying the process of cell wall development in flax, we extracted proteins from individually dissected phloem fibres (i.e. individual cells) at an early stage of secondary cell wall development, and compared these extracts to protein extracts from surrounding, non-fibre cells of the cortex, using fluorescent (DiGE) labels and 2D-gel electrophoresis, with identities assigned to some proteins by mass spectrometry.

RESULTS

The abundance of many proteins in fibres was notably different from the surrounding non-fibre cells of the cortex, with approximately 13% of the 1,850 detectable spots being significantly (> 1.5 fold, p < or = 0.05) enriched in fibres. Following mass spectrometry, we assigned identity to 114 spots, of which 51 were significantly enriched in fibres. We observed that a K+ channel subunit, annexins, porins, secretory pathway components, beta-amylase, beta-galactosidase and pectin and galactan biosynthetic enzymes were among the most highly enriched proteins detected in developing flax fibres, with many of these proteins showing electrophoretic patterns consistent with post-translational modifications.

CONCLUSION

The fibre-enriched proteins we identified are consistent with the dynamic process of secondary wall deposition previously suggested by histological and biochemical analyses, and particularly the importance of galactans and the secretory pathway in this process. The apparent abundance of beta-amylase suggests that starch may be an unappreciated source of materials for cell wall biogenesis in flax bast fibres. Furthermore, our observations confirm previous reports that correlate accumulation proteins such as annexins, and specific heat shock proteins with secondary cell wall deposition.