Two FAD3 Desaturase Genes Control the Level of Linolenic Acid in Flax Seed

Abstract

Industrial oil flax (Linum usitatissimum) and edible oil or solin flax differ markedly in seed linolenic acid levels. Despite the economic importance of low-linolenic-acid or solin flax, the molecular mechanism underlying this trait has not been established. Two independently inherited genes control the low-linolenic-acid trait in flax. Here, we identified two genes, LuFAD3A and LuFAD3B that encode microsomal desaturases capable of desaturating linoleic acid. The deduced proteins encoded by these genes shared 95.4% identity. In the low-linolenic-acid line solin 593-708, both LuFAD3A and LuFAD3B carry point mutations that produce premature stop codons. Expression of these genes in yeast (Saccharomyces cerevisiae) demonstrated that, while the wild-type proteins were capable of desaturating linoleic acid, the truncated proteins were inactive. Furthermore, the low-linolenic-acid phenotype in flax was complemented by transformation with a wild-type gene. Codominant DNA markers were developed to distinguish between null and wild-type alleles of both genes, and linolenic acid levels cosegregated with genotypes, providing further proof that LuFAD3A and LuFAD3B are the major genes controlling linolenic acid levels in flax. The level of LuFAD3 transcripts in seeds peaked at about 20 d after flowering, and transcripts were not detectable in leaf, root, or stem tissue. A dramatic reduction in transcript levels of both genes occurred in the low-linolenicacid solin line, which was likely due to nonsense-mediated decay.The seed oil of flax (Linum usitatissimum) is notable for its high level of linolenic acid, generally around 45% to 65%, which gives it a high drying quality, making it useful for industrial purposes. The development of low-linolenic-acid flax lines (Green, 1986;Rowland, 1991), known as solin or linola types, expanded the potential markets for flaxseed oil. Compared to oil from traditional flax cultivars, low-linolenic-acid oil is less subject to rapid oxidation and is thus more competitive as a cooking or salad oil (Bhatty, 1995). Two recessive genes at independent loci control the low-linolenic-acid trait in flax (Rowland, 1991). Following ethyl methanesulfonate (EMS) mutagenesis, Rowland (1991) identified an M2 seed carrying mutations in both these genes. The resulting line had a linolenic acid content of less than 2% compared to levels of approximately 49% in the wild-type parent McGregor. Similarly, Green and Marshall (1984) isolated two EMS-derived mutants with linolenic acid contents of approximately 30% and by recombining these lines were able to obtain plants with linolenic acid contents below 2% (Green, 1986). In contrast to the dramatic reduction of linolenic acid in seeds, the levels in leaf tissue remained unchanged (Tonnet and Green, 1987).Linolenic acid is produced through the desaturation of linoleic acid by omega-3/delta-15 desaturases. In plants, this reaction occurs both in the plastids and in the endoplasmic reticulum (ER). Arabidopsis (Arabidopsis thaliana) carries two plastidial desaturases...

Identification of bifunctional Δ12/ω3 fatty acid desaturases for improving the ratio of ω3 to ω6 fatty acids in microbes and plants

“…Seed-specific expression of Arabidopsis 3 desaturase (FAD3) in soybean resulted in 53.0%TFA ALA (34). Seed-specific expression of a flax 3 desaturase in a double mutant of flax lacking both FAD3 genes resulted in 41.0%TFA ALA in seeds (32). Soybean is an ideal choice for the economic production of 3 LC-PUFAs in plants.…”

Devolopmental and growth temperature regulation of omega-3 fatty acid desaturase genes in safflower (Carthamus tinctorius L.)

“…In oil crops, FAD3 desaturase is an essential enzyme in the production of LNA during seed development. The regulation of the FAD3 gene has proven a successful strategy for modifying the LNA properties of seed oils (Bilyeu et al, 2003;Vrinten et al, 2005;Kim et al, 2008). The presence of FAD3 in safflower raised the question of why it does not contribute LNA synthesis in safflower seeds.…”

“…Three independent microsomal ω-3 desaturase genes, named GmFAD3A, GmFAD3B, and GmFAD3C, have been shown to contribute to soybean seed linolenic acid levels (Bilyeu et al, 2003). Two FAD3 desaturase genes were identified in flax (LuFAD3A and LuFAD3B) (Vrinten et al, 2005) and periila (PfFAD3A and PfFAD3B), which control the level of linolenic acid in seeds (Kim et al, 2008). Genes encoding plastidial ω-3 desaturases (FAD7/8) were isolated from Arabidopsis thaliana (Iba et al, 1993;Gibson et al, 1994), Glycine max (van de Loo and Somerville, 1994), Zea mays (Berberich et al, 1998), and Descurainia sophia (Tang et al, 2007).…”

Biochemical diversity of fatty acid composition in flax from VIR genetic collection and effect of environment on its development

“…н.). Мутация в гене LuFAD3B в большей степени снижает содержание линолено-вой кислоты, чем LuFAD3A (Vrinten et al, 2005).…”

“…У арабидоп-сиса, как модельного объекта для изучения генетического контроля биосин-теза запасных липидов (Browse, Somerville, 1994, Ohlrogge, Browse, 1995, Chapman et al, 2012, было установлено, что изменение температуры вли-яет на проявление дефектных генов, контролирующих биосинтез ЖК, затрагивающее размеры растения, ан-тоциановую окраску и появление некрозов (Ohlrogge, Browse, 1995). У льна мутанты с нарушением биосин-теза ЖК получены только для генов fad2 и fad3, и у них не выявлено плейотропного эффекта на другие признаки (Vrinten et al, 2005;Thambugala et al, 2013;Chen et al, 2015).…”