Genetic control of polyunsaturated fatty acid biosynthesis in flax (Linum usitatissimum) seed oil

Diversity of Linum genetic resources in global genebanks: from agro-morphological characterisation to novel genomic technologies - a review

Linseed or flaxseed is a well-recognized nutritional food with nutraceutical properties owing to high omega-3 fatty acid (α-Linolenic acid), dietary fiber, quality protein, and lignan content. Currently, linseed enjoys the status of a 'superfood' and its integration in the food chain as a functional food is evolving continuously as seed constituents are associated with lowering the risk of chronic ailments, such as heart diseases, cancer, diabetes, and rheumatoid arthritis. This crop also receives much attention in the handloom and textile sectors as the world's coolest fabric linen is made up of its stem fibers which are endowed with unique qualities such as luster, tensile strength, density, bio-degradability, and non-hazardous nature. Worldwide, major linseed growing areas are facing erratic rainfall and temperature patterns affecting flax yield, quality, and response to biotic stresses. Amid such changing climatic regimes and associated future threats, diverse linseed genetic resources would be crucial for developing cultivars with a broad genetic base for sustainable production. Furthermore, linseed is grown across the world in varied agro-climatic conditions; therefore it is vital to develop niche-specific cultivars to cater to diverse needs and keep pace with rising demands globally. Linseed genetic diversity conserved in global genebanks in the form of germplasm collection from natural diversity rich areas is expected to harbor genetic variants and thus form crucial resources for breeding tailored crops to specific culinary and industrial uses. Global genebank collections thus potentially play an important role in supporting sustainable agriculture and food security. Currently, approximately 61,000 germplasm accessions of linseed including 1,127 wild accessions are conserved in genebanks/institutes worldwide. This review analyzes the current status of Linum genetic resources in global genebanks, evaluation for agro-morphological traits, stress tolerance, and nutritional profiling to promote their effective use for sustainable production and nutrition enhancement in our modern diets.

Identification of LncRNAs and Functional Analysis of ceRNA Related to Fatty Acid Synthesis during Flax Seed Development

Flax is a flowering plant cultivated for its oil and contains various unsaturated fatty acids. Linseed oil is known as the "deep-sea fish oil" of plants, and is beneficial to brain and blood lipids, among other positive effects. Long non-coding RNAs (lncRNAs) play an important role in plant growth and development. There are not many studies assessing how lncRNAs are related to the fatty acid synthesis of flax. The relative oil contents of the seeds of the variety Heiya NO.14 (for fiber) and the variety Macbeth (for oil) were determined at 5 day, 10 day, 20 day, and 30 day after flowering. We found that 10-20 day is an important period for ALA accumulation in the Macbeth variety. The strand-specific transcriptome data were analyzed at these four time points, and a series of lncRNAs related to flax seed development were screened. A competing endogenous RNA (ceRNA) network was constructed and the accuracy of the network was verified using qRT-PCR. MSTRG.20631.1 could act with miR156 on the same target, squamosa promoter-binding-like protein (SPL), to influence fatty acid biosynthesis through a gluconeogenesis-related pathway during flax seed development. This study provides a theoretical basis for future studies assessing the potential functions of lncRNAs during seed development.

Development and Complex Application of Methods for the Identification of Mutations in the FAD3A and FAD3B Genes Resulting in the Reduced Content of Linolenic Acid in Flax Oil

Flax is grown worldwide for seed and fiber production. Linseed varieties differ in their oil composition and are used in pharmaceutical, food, feed, and industrial production. The field of application primarily depends on the content of linolenic (LIN) and linoleic (LIO) fatty acids. Inactivating mutations in the FAD3A and FAD3B genes lead to a decrease in the LIN content and an increase in the LIO content. For the identification of the three most common low-LIN mutations in flax varieties (G-to-A in exon 1 of FAD3A substituting tryptophan with a stop codon, C-to-T in exon 5 of FAD3A leading to arginine to a stop codon substitution, and C-to-T in exon 2 of FAD3B resulting in histidine to tyrosine substitution), three approaches were proposed: (1) targeted deep sequencing, (2) high resolution melting (HRM) analysis, (3) cleaved amplified polymorphic sequences (CAPS) markers. They were tested on more than a thousand flax samples of various types and showed promising results. The proposed approaches can be used in marker-assisted selection to choose parent pairs for crosses, separate heterogeneous varieties into biotypes, and select genotypes with desired homozygous alleles of the FAD3A and FAD3B genes at the early stages of breeding for the effective development of varieties with a particular LIN and LIO content, as well as in basic studies of the molecular mechanisms of fatty acid synthesis in flax seeds to select genotypes adequate to the tasks.

Overexpression of WRINKLED1 improves the weight and oil content in seeds of flax (Linum usitatissimum L.)

Seeds of flax (Linum usitatissimum L.) are highly rich in both oil and linolenic acid (LIN). It is crucial for flax agricultural production to identify positive regulators of fatty acid biosynthesis. In this study, we find that WRINKLED1 transcription factors play important positive roles during flax seed oil accumulation. Two WRINKLED1 genes, LuWRI1a and LuWRI1b, were cloned from flax, and LuWRI1a was found be expressed predominantly in developing seeds during maturation. Overexpression of LuWRI1a increased seed size, weight, and oil content in Arabidopsis and increased seed storage oil content in transgenic flax without affecting seed production or seed oil quality. The rise in oil content in transgenic flax seeds was primarily attributable to the increase in seed weight, according to a correlational analysis. Furthermore, overexpression or interference of LuWRI1a upregulated the expression of genes in the fatty acid biosynthesis pathway and LAFL genes, and the expression level of WRI1 was highly significantly positively associated between L1L, LEC1, and BCCP2. Our findings give a theoretical scientific foundation for the future application of genetic engineering to enhance the oil content of plant seeds.

Changes in Fatty Acid, Tocopherol and Sterol Contents of Oils Extracted from Several Vegetable Seeds

Oil contents of seeds changed between 15.89 g/100 g (purslane) and 38.97 g/100 g (black radish). Palmitic acid contents of oil samples were found between 2.2 g/100 g (turnip) and 15.0 g/100 g (purslane). While oleic acid contents of oil samples change between 12.1% (turnip) and 69.8% (purple carrot), linoleic acid contents of oils were determined between 8.9% (black radish) and 57.0% (onion). The highest linolenic acid was found in purslane oil (26.7%). While α-tocopherol contents of oil samples range from 2.01 mg/kg (purple carrot) to 903.01 mg/kg (onion), γ-tocopherol contents of vegetable seed oils changed between 1.14 mg/kg (curly lettuce) and 557.22 mg/kg (purslane). While campesterin contents of seed oils change between 203.2 mg/kg (purple carrot) and 2808.5 mg/kg (cabbage Yalova), stosterin contents of oil samples varied from 981.5 (curly lettuce) to 4843.3 mg/kg (purslane). The highest brassicasterin and δ5-avenasterin were found in red cabbage oil (894.5 mg/kg) and purslane seed oils (971.3 mg/kg), respectively. Total sterol contents of seed oils changed between 2960.4 mg/kg (purple carrot) and 9185.1 mg/kg (purslane). According to the results, vegetable seeds have different bioactive compound such as fatty acid, tocopherol and phytosterol.

Engineering Trienoic Fatty Acids into Cottonseed Oil Improves Low-Temperature Seed Germination, Plant Photosynthesis and Cotton Fiber Quality

Alpha-linolenic acid (ALA, 18:3Δ9,12,15) and γ-linolenic acid \ (GLA, 18:3Δ6,9,12) are important trienoic fatty acids, which are beneficial for human health in their own right, or as precursors for the biosynthesis of long-chain polyunsaturated fatty acids. ALA and GLA in seed oil are synthesized from linoleic acid (LA, 18:2Δ9,12) by the microsomal ω-3 fatty acid desaturase (FAD3) and Δ6 desaturase (D6D), respectively. Cotton (Gossypium hirsutum L.) seed oil composition was modified by transforming with an FAD3 gene from Brassica napus and a D6D gene from Echium plantagineum, resulting in approximately 30% ALA and 20% GLA, respectively. The total oil content in transgenic seeds remained unaltered relative to parental seeds. Despite the use of a seed-specific promoter for transgene expression, low levels of GLA and increased levels of ALA were found in non-seed cotton tissues. At low temperature, the germinating cottonseeds containing the linolenic acid isomers elongated faster than the untransformed controls. ALA-producing lines also showed higher photosynthetic rates at cooler temperature and better fiber quality compared to both untransformed controls and GLA-producing lines. The oxidative stability of the novel cottonseed oils was assessed, providing guidance for potential food, pharmaceutical and industrial applications of these oils.

Variation of fatty acid composition in seed oil in the collection of induced oil flax (Linum humile Mill.) mutants

A wide variety of application fields for flax seeds requires for breeders to develop new varieties with different characteristics, corresponding to the intended final product. The method of experimental mutagenesis is one of the ways to solve this problem. This method allows mutant lines with an array of morphometric and biochemical traits to be created from a single species and within a relatively short period of time. The article demonstrates that treatment of Linum humile Mill. seeds of the cultivars Iceberg and Solnech-ny with the new chemical mutagens DG-2, DG-6, DG-7, DG-9 (derivatives of dimethyl sulfate (DMS)) as well as with the mutagens DMS and EMS resulted in the production of mutant lines and accessions with altered morphometric and biochemical parameters. Seeds of the initial cultivars were treated with 0.5 and 0.05 % aqueous solutions of the above mentioned substances and planted in the field to raise M1, M2, and M3generations. Ultimately, 27 types of mutations were identified and subdivided into five groups by morphometric characteristics. The fatty acid composition of seed oil for the isolated mutant specimens was studied: the content of palmitic, stearic, oleic, linoleic (w6) and lino-lenic (w3) acids, as well as the w6/w3 ratio. The statistical analysis showed significant distinctions between the mutant lines in the biochemical composition of the oil. A strong negative correlation between the content of linoleic and linolenic acids was demonstrated, as well as a positive relationship of average strength between the content of stearic and oleic acids for the both varieties. The mutant accessions obtained can be used as donor material for conducting breeding work on flax in various directions.

Multiplexed shotgun sequencing reveals congruent three-genome phylogenetic signals for four botanical sections of the flax genus Linum

A genome-wide detection of phylogenetic signals by next generation sequencing (NGS) has recently emerged as a promising genomic approach for phylogenetic analysis of non-model organisms. Here we explored the use of a multiplexed shotgun sequencing method to assess the phylogenetic relationships of 18 Linum samples representing 16 species within four botanical sections of the flax genus Linum. The whole genome DNAs of 18 Linum samples were fragmented, tagged, and sequenced using an Illumina MiSeq. Acquired sequencing reads per sample were further separated into chloroplast, mitochondrial and nuclear sequence reads. SNP calls upon genome-specific sequence data sets revealed 6143 chloroplast, 2673 mitochondrial, and 19,562 nuclear SNPs. Phylogenetic analyses based on three-genome SNP data sets with and without missing observations showed congruent three-genome phylogenetic signals for four botanical sections of the Linum genus. Specifically, two major lineages showing a separation of Linum-Dasylinum sections and Linastrum-Syllinum sections were confirmed. The Linum section displayed three major branches representing two major evolutionary stages leading to cultivated flax. Cultivated flax and its immediate progenitor were formed as its own branch, genetically more closely related to L. decumbens and L. grandiflorum with chromosome count of eight, and distantly apart from six other species with chromosome count of nine. Five species of the Linastrum and Syllinum sections were genetically more distant from cultivated flax, but they appeared to be more closely related to each other, even with variable chromosome counts. These findings not only provide the first evidence of congruent three-genome phylogenetic pathways within the Linum genus, but also demonstrate the utility of the multiplexed shotgun sequencing in acquisition of three-genome phylogenetic signals of non-model organisms.

Structural organization of fatty acid desaturase loci in linseed lines with contrasting linolenic acid contents

Flax (Linum usitatissimum L.), the richest crop source of omega-3 fatty acids (FAs), is a diploid plant with an estimated genome size of ~370 Mb and is well suited for studying genomic organization of agronomically important traits. In this study, 12 bacterial artificial chromosome clones harbouring the six FA desaturase loci sad1, sad2, fad2a, fad2b, fad3a and fad3b from the conventional variety CDC Bethune and the high linolenic acid line M5791 were sequenced, analysed and compared to determine the structural organization of these loci and to gain insights into the genetic mechanisms underlying FA composition in flax. With one gene every 3.2-4.6 kb, the desaturase loci have a higher gene density than the genome's average of one gene per 7.8-8.2 kb. The gene order and orientation across the two genotypes were generally conserved with the exception of the sad1 locus that was predicted to have additional genes in CDC Bethune. High sequence conservation in both genic and intergenic regions of the sad and fad2b loci contrasted with the significant level of variation of the fad2a and fad3 loci, with SNPs being the most frequently observed mutation type. The fad2a locus had 297 SNPs and 36 indels over ~95 kb contrasting with the fad2b locus that had a mere seven SNPs and four indels in ~110 kb. Annotation of the gene-rich loci revealed other genes of known role in lipid or carbohydrate metabolic/catabolic pathways. The organization of the fad2b locus was particularly complex with seven copies of the fad2b gene in both genotypes. The presence of Gypsy, Copia, MITE, Mutator, hAT and other novel repeat elements at the desaturase loci was similar to that of the whole genome. This structural genomic analysis provided some insights into the genomic organization and composition of the main desaturase loci of linseed and of their complex evolution through both tandem and whole genome duplications.

Influence of cadmium and mycorrhizal fungi on the fatty acid profile of flax (Linum usitatissimum) seeds

BACKGROUND

The soil environment can affect not only the quantity of crops produced but also their nutritional quality. We examined the combined effects of below-ground cadmium (0, 5, and 15 ppm) and mycorrhizal fungi (presence and absence) on the concentration of five major fatty acids within flax seeds (Linum usitatissimum).

RESULTS

Plants grown with mycorrhizal fungi produced seeds that contained higher concentrations of unsaturated (18:1, 18:2 and 18:3), but not saturated (16:0 and 18:0) fatty acids. The effects of mycorrhizal fungi on the concentration of unsaturated fatty acids in seeds were most pronounced when plant roots were exposed to 15 ppm Cd (i.e. the concentrations of 18:1, 18:2 and 18:3 increased by 169%, 370% and 150%, respectively).

CONCLUSIONS

The pronounced effects of mycorrhizal fungi on the concentration of unsaturated fatty acids at 15 ppm Cd may have been due to the presence of elevated levels of Cd within seeds. Our results suggest that, once the concentration of cadmium within seeds reaches a certain threshold, this heavy metal may improve the efficiency of enzymes that convert saturated fatty acids to unsaturated fatty acids.

QTL for fatty acid composition and yield in linseed (Linum usitatissimum L.)

The combined SSR-SNP map and 20 QTL for agronomic and quality traits will assist in marker assisted breeding as well as map-based cloning of key genes in linseed. Flax is an important nutraceutical crop mostly because it is a rich source of omega-3 fatty acids and antioxidant compounds. Canada is the largest producer and exporter of oilseed flax (or linseed), creating a growing need to improve crop productivity and quality. In this study, a genetic map was constructed based on selected 329 single nucleotide polymorphic markers and 362 simple sequence repeat markers using a recombinant inbred line population of 243 individuals from a cross between the Canadian varieties CDC Bethune and Macbeth. The genetic map consisted of 15 linkage groups comprising 691 markers with an average marker density of one marker every 1.9 cM. A total of 20 quantitative trait loci (QTL) were identified corresponding to 14 traits. Three QTL each for oleic acid and stearic acid, two QTL each for linoleic acid and iodine value and one each for palmitic acid, linolenic acid, oil content, seed protein, cell wall, straw weight, thousand seed weight, seeds per boll, yield and days to maturity were identified. The QTL for cell wall, straw weight, seeds per boll, yield and days to maturity all co-located on linkage group 4. Analysis of the candidate gene regions underlying the QTL identified proteins involved in cell wall and fibre synthesis, fatty acid biosynthesis as well as their metabolism and yield component traits. This study provides the foundation for assisting in map-based cloning of the QTL and marker assisted selection of a wide range of quality and agronomic traits in linseed and potentially fibre flax.

Characterization of a stearoyl-acyl carrier protein desaturase gene family from chocolate tree, Theobroma cacao L

In plants, the conversion of stearoyl-ACP to oleoyol-ACP is catalyzed by a plastid-localized soluble stearoyl-acyl carrier protein (ACP) desaturase (SAD). The activity of SAD significantly impacts the ratio of saturated and unsaturated fatty acids, and is thus a major determinant of fatty acid composition. The cacao genome contains eight putative SAD isoforms with high amino acid sequence similarities and functional domain conservation with SAD genes from other species. Sequence variation in known functional domains between different SAD family members suggested that these eight SAD isoforms might have distinct functions in plant development, a hypothesis supported by their diverse expression patterns in various cacao tissues. Notably, TcSAD1 is universally expressed across all the tissues, and its expression pattern in seeds is highly correlated with the dramatic change in fatty acid composition during seed maturation. Interestingly, TcSAD3 and TcSAD4 appear to be exclusively and highly expressed in flowers, functions of which remain unknown. To test the function of TcSAD1 in vivo, transgenic complementation of the Arabidopsis ssi2 mutant was performed, demonstrating that TcSAD1 successfully rescued all AtSSI2 related phenotypes further supporting the functional orthology between these two genes. The identification of the major SAD gene responsible for cocoa butter biosynthesis provides new strategies for screening for novel genotypes with desirable fatty acid compositions, and for use in breeding programs to help pyramid genes for quality and other traits such as disease resistance.

Fatty acid, tocopherol and squalene contents of Rosaceae seed oils

BACKGROUND

The aim of current study is to establish the composition of these seeds belong to Rosaceae family with respect to fatty acid, tocopherol and squalene content.

RESULTS

The oil contents of seeds varied between 3.49 (Cotoneaster bullatus) to 46.15 g/100 g (Prunus tenella). The main fatty acids of seed oils were oleic (6.50 - 67.11 %), linoleic (22.08 - 68.62 %) and 20:1n-7 (0.10 - 61.59 %). As observed, the oils of seed were rich in linoleic and oleic acids. Total tocopherol contents ranged between 7.06 mg/100 g (Prunus tenella) to 165.74 mg/100 g (Potentilla glandulosa ssp. pseudorupestris). The major tocopherols were γ-tocopherol, ranging from 2.08 mg/100 g to 106.01 mg/100 g; α-tocopherol ranging from 2.86 mg100 g to 74.26 mg/100 g and δ-tocopherol ranging used in this experiment were found between 0.02 mg/100 g (Alchemilla caucasica) to o.29 mg/100 g (Cotoneaster simonsii).

CONCLUSIONS

These results show that Rosaceae seed oils can be a potential saurce of valuable oil which might be useful for the evaluation of dietary information in important food crops and other industrial applications.

Diversity analysis in Indian genotypes of linseed (Linum usitatissimum L.) using AFLP markers

AFLP fingerprinting of 45 Indian genotypes of linseed was carried out to determine the genetic relationship among them. Sixteen primer combinations produced 1142 fragments with 1129 as polymorphic and 13 as monomorphic fragments. Polymorphic fragments varied from 44 (E-ACA/M-CTA) to 94 (E-AGC/M-CAC) with an average of 70.6 fragments per primer combination. The frequency of polymorphism varied from 93.7% to 100% with an average of 98.8% across all the genotypes. The PIC value ranged from 0.19 to 0.31 with an average of 0.23 per primer combination. The primer pair E-AGC/M-CAC showed the maximum PIC value (0.31) followed by E-AGC/M-CAG (0.29), E-AAC/M-CAG (0.26) and E-AGC/M-CTA (0.25). Resolving power (RP) and marker index (MI) varied from 13.73 to 43.50 and 8.81 to 28.91 respectively. The Jaccard's similarity coefficient varied from 0.16 to 0.57 with an average of 0.26 ± 0.05. The maximum genetic similarities (57%) were detected between genotypes Him Alsi-1 and Him Alsi-2, followed by Him Alsi-1 and GS41 and GS41 and LC-54. The genotypes R-552, Himani, RKY-14, Meera, Indira Alsi-32 and Suyog were found to be more divergent genotypes. The NJ clustering grouped all the 45 genotypes into three major clusters. In general the genotypes of cluster III had high oil content and those of cluster I had low oil content. At the population level, within population variance was much higher than between populations variance.

Fatty acid composition and desaturase gene expression in flax (Linum usitatissimum L.)

Little is known about the relationship between expression levels of fatty acid desaturase genes during seed development and fatty acid (FA) composition in flax. In the present study, we looked at promoter structural variations of six FA desaturase genes and their relative expression throughout seed development. Computational analysis of the nucleotide sequences of the sad1, sad2, fad2a, fad2b, fad3a and fad3b promoters showed several basic transcriptional elements including CAAT and TATA boxes, and several putative target-binding sites for transcription factors, which have been reported to be involved in the regulation of lipid metabolism. Using semi-quantitative reverse transcriptase PCR, the expression patterns throughout seed development of the six FA desaturase genes were measured in six flax genotypes that differed for FA composition but that carried the same desaturase isoforms. FA composition data were determined by phenotyping the field grown genotypes over four years in two environments. All six genes displayed a bell-shaped pattern of expression peaking at 20 or 24 days after anthesis. Sad2 was the most highly expressed. The expression of all six desaturase genes did not differ significantly between genotypes (P = 0.1400), hence there were no correlations between FA desaturase gene expression and variations in FA composition in relatively low, intermediate and high linolenic acid genotypes expressing identical isoforms for all six desaturases. These results provide further clues towards understanding the genetic factors responsible for FA composition in flax.

Phylogenetic pinpointing of a paleopolyploidy event within the flax genus (Linum) using transcriptomics

BACKGROUND AND AIMS

Cultivated flax (Linum usitatissimum) is known to have undergone a whole-genome duplication around 5-9 million years ago. The aim of this study was to investigate whether other whole-genome duplication events have occurred in the evolutionary history of cultivated flax. Knowledge of such whole-genome duplications will be important in understanding the biology and genomics of cultivated flax.

METHODS

Transcriptomes of 11 Linum species were sequenced using the Illumina platform. The short reads were assembled de novo and the DupPipe pipeline was used to look for signatures of polyploidy events from the age distribution of paralogues. In addition, phylogenies of all paralogues were assembled within an estimated age window of interest. These phylogenies were assessed for evidence of a paleopolyploidy event within the genus Linum.

KEY RESULTS

A previously unknown paleopolyploidy event that occurred 20-40 million years ago was discovered and shown to be specific to a clade within Linum containing cultivated flax (L. usitatissimum) and other mainly blue-flowered species. The finding was supported by two lines of evidence. First, a significant change of slope (peak) was shown in the age distribution of paralogues that was phylogenetically restricted to, and ubiquitous in, this clade. Second, a large number of paralogue phylogenies were retrieved that are consistent with a polyploidy event occurring within that clade.

CONCLUSIONS

The results show the utility of multi-species transcriptomics for detecting whole-genome duplication events and demonstrate that that multiple rounds of polyploidy have been important in shaping the evolutionary history of flax. Understanding and characterizing these whole-genome duplication events will be important for future Linum research.

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.

Genotyping by RAD sequencing enables mapping of fatty acid composition traits in perennial ryegrass (Lolium perenne (L.))

Perennial ryegrass (Lolium perenne L.) is the most important forage crop in temperate livestock agriculture. Its nutritional quality has significant impact on the quality of meat and milk for human consumption. Evidence suggests that higher energy content in forage can assist in reducing greenhouse gas emissions from ruminants. Increasing the fatty acid content (especially α-linolenic acid, an omega-3 fatty acid) may thus contribute to better forage, but little is known about the genetic basis of variation for this trait. To this end, quantitative trait loci (QTLs) were identified associated with major fatty acid content in perennial ryegrass using a population derived from a cross between the heterozygous and outbreeding high-sugar grass variety AberMagic and an older variety, Aurora. A genetic map with 434 restriction-associated DNA (RAD) and SSR markers was generated. Significant QTLs for the content of palmitic (C16:0) on linkage groups (LGs) 2 and 7; stearic (C18:0) on LGs 3, 4 and 7; linoleic (C18:2n-6) on LGs 2 and 5; and α-linolenic acids (C18:3n-3) on LG 1 were identified. Two candidate genes (a lipase and a beta-ketoacyl CoA synthase), both associated with C16:0, and separately with C18:2n-6 and C18:0 contents, were identified. The physical positions of these genes in rice and their genetic positions in perennial ryegrass were consistent with established syntenic relationships between these two species. Validation of these associations is required, but the utility of RAD markers for rapid generation of genetic maps and QTL analysis has been demonstrated for fatty acid composition in a global forage crop.

Characteristics of grains and oils of four different oats (Avena sativaL.) cultivars growing in Turkey

Some physical and chemical properties of four oat (Avena sativa L.) varieties (BDMY-6, BDMY-7, Che-Chois and Y-2330) harvested from Konya in Turkey were investigated. The weight of the grain, moisture, crude protein, crude ash, crude fibre, crude energy, crude oil and water-soluble extract contents of all oat variety grains were analysed. Contents of aluminium, calcium, cadmium, phosphorus, magnesium, zinc, lead, potassium and manganese were also determined in the oat grains. The specific gravity, refractive index, free fatty acids, peroxide value, saponification number and unsaponifiable matter were determined in the grain oil. Tocopherol contents of these four oat grain oils were measured. Palmitic acid (15.72%), oleic acid (33.97-51.26%) and linoleic acid (22.80-35.90%) were found to be rich in protein, oil, fibre, unsaturated fatty acids and minerals, suggesting that they may be valuable for food uses. Due to high nutritive values, it is recommended to process for healthy food products.

Advances in the molecular genetic analysis of the flax-flax rust interaction

The L6 and M rust-resistance genes, representing two of the five rust-resistance gene loci in flax (Linum usitatissimum), have been cloned. The molecular data are fully consistent with earlier genetic data: the L locus is a single gene with multiple alleles expressing different rust resistance specificities, and the M locus is complex, containing an array of about 15 similar genes. Thus, while L6 and M resistance genes have 86% nucleotide identity, their locus structure is very different. These genes encode products belonging to the nucleotide binding site-leucine-rich repeat class of disease-resistance proteins. Analysis of alleles from the L locus and chimeric genes is providing evidence suggesting that important specificity determinants occur in the C-terminal half of the proteins, the region containing the leucine-rich repeats. The isolation and characterization of the rust (Melampsora lini) avirulence genes that correspond to the cloned rust-resistance genes is one of the major challenges remaining to the understanding of this system.

Biosynthesis of linolenate in developing embryos and cell-free preparations of high-linolenate linseed (Linum usitatissimum) and low-linolenate mutants

Biosynthesis of alpha-linolenate was investigated in developing embryos of the high-linolenic (45%) linseed cv. Glenelg, two mutant lines (M1589 and M1722) having reduced linolenic acid content (30%), and a very low linolenic (2%) genotype (Zero) obtained by recombination of the M1589 and M1722 mutations. Glenelg embryos showed an exponential rate of linolenate synthesis that paralleled their exponential pattern of triacylglycerol accumulation. The Zero line, although showing a pattern of triacylglycerol accumulation similar to that of Glenelg, accumulated linolenate at only a very low and constant rate throughout embryo development. An NADH- and O2-dependent decrease in oleate and increase in linolenate content of phosphatidylcholine was observed in dilute homogenates prepared from Glenelg embryos at 21 days after flowering, indicating active oleoyl- and linoleoyl-phosphatidylcholine desaturases in these preparations. While oleate decreased similarly in both sn positions of phosphatidylcholine, the increase in linolenate was confined mostly to the sn-2 position. Homogenates prepared from the mutant lines showed decreases in oleoyl-phosphatidylcholine similar to those of the wild-type Glenelg, whereas the increase in linolenoyl-phosphatidylcholine was substantially lower in M1589 and M1722 and barely detected in Zero. In vivo labeling experiments with detached embryos at 17 days after flowering, as well as analysis of endogenous linolenate content in various lipids, indicated that only delta 15-phospholipid desaturases, and not delta 15-galactolipid desaturases, were affected by the mutations. Embryos from M1722 had amounts of both radioactive and endogenous linolenate at position sn-1 of phosphatidylcholine that were close to those of the wild-type embryos, whereas M1589 had only 30 and 50% of these levels, respectively. The regulation of linolenic acid content in oilseeds is discussed on the basis of the results obtained.