Storage lipid accumulation and acyltransferase action in developing flaxseed

Abstract

Investigations of storage lipid synthesis in developing flaxseed (Linum usitatissimum) provide useful information for designing strategies to enhance the oil content and nutritional value of this crop. Lipid content and changes in the FA composition during seed development were examined in two cultivars of flax (AC Emerson and Vimy). The oil content on a dry weight basis increased steadily until about 20 d after flowering (DAF). The proportion of alpha-linolenic acid (alpha-18:3, 18:3cisDelta9,12,15) in TAG increased during seed development in both cultivars while the proportions of linoleic acid (18:2cisDelta9,12) and saturated FA decreased. The developmental and substrate specificity characteristics of microsomal DAG acyltransferase (DGAT, EC 2.3.1.20) and lysophosphatidic acid acyltransferase (LPAAT, EC 2.3.1.51) were examined using cultivar AC Emerson. The maximal acyltransferase specific activities occurred in the range of 8-14 DAF, during rapid lipid accumulation on a per seed basis. Acyl-CoA of EPA (20:5cisDelta5,8,11,14,17) or DHA (22:6 cis4,7,10,13,16,19) were included in the specificity studies. DGAT displayed enhanced specificity for alpha-18:3-CoA, whereas the preferred substrate of [PAAT was 18:2-CoA. Both enzymes could use EPA- or DHA-CoA to varying extents. Developing flax embryos were able to take up and incorporate these nutritional FA into TAG and other intermediates in the TAG-formation pathway. This study suggests that if the appropriate acyl-CoA-dependent desaturation/elongation pathways are introduced and efficiently expressed in flax, this may lead to the conversion of alpha-18:3-CoA into EPA-CoA, thereby providing an activated substrate for TAG formation.

In Vivo and in Vitro Evidence for Biochemical Coupling of Reactions Catalyzed by Lysophosphatidylcholine Acyltransferase and Diacylglycerol Acyltransferase

“…As shown in Fig. 5, DGAT1-1 exhibited small but significant changes of substrate specificity toward the acyl-CoA substrates, and the highest specificity was observed with 18:3-CoA, which is in close agreement with substrate specificity data for overall microsomal DGAT activity from developing flax embryos (34).…”

Characteristics of High α‐Linolenic Acid Accumulation in Seed Oils

“…The data from both lipid analysis and Northern blot highly suggest that the reduced linolenic acid content in soybean compared with high 18:3 accumulators is mainly due to the lower transcript level of x-3 desaturase. Byrum et al [33] found that the reduced 18:3 concentration in the soybean genotype A5 was at least partially the result of a microsomal x-3 desaturase gene with a reduced activity. Collectively, these results indicate that one can obtain B. napus, soybeans or other oilseed crops that accumulate high x-3 fatty acid levels simply by increasing expression of the x-3 desaturase gene by use of a strong promoter or trans-activation.…”

Pathways of Lipid Metabolism in Marine Algae, Co-Expression Network, Bottlenecks and Candidate Genes for Enhanced Production of EPA and DHA in Species of Chromista

“…The acyltransferases residing in the ER are required for the esterification of FAs to the desired sn -position of the glycerol-backbone. Most likely the acyltransferases involved in the n -3 LC-PUFA synthesis are similar to those in plants (lysophospholipid acyltransferases (LPLAT), acyl-CoA:glycerol-3-phosphate acyltransferase (GPAT) and acyl-CoA:lysophosphatidic acyltransferase (LPAAT)) [117,118]. The latter two represent enzymes of the Kennedy pathway in the ER [119].…”

“…Overexpression of genes encoding high substrate specific acyltransferases would lead to a higher esterification rate of acyl-donor to a specific sn -position of the glycerol-3-phosphate or the PC. The two ER-localized enzymes of the Kennedy pathway (GPAT and LPAAT) and the LPLAT are responsible for the incorporation of activated FAs into membrane lipids, or precursors of membrane lipids [117,118]. Recently, it was shown that an ER-membrane bound TpGPAT from the marine diatom T. pseudonana affected FA composition and accumulation in triacylglycerides and phospholipids by overexpression in a GPAT-deficient yeast strain [128].…”