Two Acyltransferases Contribute Differently to Linolenic Acid Levels in Seed Oil

Abstract

ORCID IDs: 0000-0001-6929-7859 (S.M.); 0000-0003-3152-0394 (D.S.); 0000-0001-8255-3255 (C.H.); 0000-0003-0489-3072 (K.C.); 0000-0002-9888-7003 (I.F.).Acyltransferases are key contributors to triacylglycerol (TAG) synthesis and, thus, are of great importance for seed oil quality. The effects of increased or decreased expression of ACYL-COENZYME A:DIACYLGLYCEROL ACYLTRANSFERASE1 (DGAT1) or PHOSPHOLIPID:DIACYLGLYCEROL ACYLTRANSFERASE (PDAT) on seed lipid composition were assessed in several Camelina sativa lines. Furthermore, in vitro assays of acyltransferases in microsomal fractions prepared from developing seeds of some of these lines were performed. Decreased expression of DGAT1 led to an increased percentage of 18:3n-3 without any change in total lipid content of the seed. The tri-18:3 TAG increase occurred predominantly in the cotyledon, as determined with matrix-assisted laser desorption/ionization-mass spectrometry, whereas species with two 18:3n-3 acyl groups were elevated in both cotyledon and embryonal axis. PDAT overexpression led to a relative increase of 18:2n-6 at the expense of 18:3n-3, also without affecting the total lipid content. Differential distributions of TAG species also were observed in different parts of the seed. The microsomal assays revealed that C. sativa seeds have very high activity of diacylglycerol-phosphatidylcholine interconversion. The combination of analytical and biochemical data suggests that the higher 18:2n-6 content in the seed oil of the PDAT overexpressors is due to the channeling of fatty acids from phosphatidylcholine into TAG before being desaturated to 18:3n-3, caused by the high activity of PDAT in general and by PDAT specificity for 18:2n-6. The higher levels of 18:3n-3 in DGAT1-silencing lines are likely due to the compensatory activity of a TAG-synthesizing enzyme with specificity for this acyl group and more desaturation of acyl groups occurring on phosphatidylcholine.

Acyl-CoA:lysophosphatidylcholine acyltransferases (LPCATs) of Camelina sativa seeds: biochemical properties and function

“…The mature seeds of C. sativa contained approximately 80% unsaturated fatty acids (18:3, 37%: 18:2, 18%; 20:1, 13%; and 18:1, 12%, approximately). Similar fatty acid compositions of acyl lipids of C. sativa seeds have also been reported by others (Zubr 1997;Gugel and Falk 2006;Rodriguez-Rodriguez et al 2013;Marmon et al 2017). After 31 DAF, the net increase in the acyl lipids in C. sativa seeds was not recorded.…”

Spatial analysis of lipid metabolites and expressed genes reveals tissue‐specific heterogeneity of lipid metabolism in high‐ and low‐oil Brassica napus L. seeds

“…The transcript levels of PAP were also higher in the OC and EA of ZS11 than in WH5557, whereas DGAT transcript levels (sum of DGAT1 and DGAT2 ) were similar in the OC and EA tissues between two accessions (Figures d and a). In another TAG biosynthesis route, lysophosphatidylcholine acyltransferase (LPCAT) transfers an acyl chain from the acyl‐CoA pool to LPC to form PC, and then via phospholipid:diacylglycerol acyltransferase (PDAT) from PC to DAG to form TAG (Chapman and Ohlrogge, ; Marmon et al ., ). Somewhat contradictory with expectations (if LPCAT and PDAT were important in determining oil content differences between these two accessions), the transcript levels of LPCAT were highest in all of the seed tissues of WH5557 compared with ZS11.…”

“…MALDI‐MS imaging (MALDI‐MSI) has been used to study the spatial distribution of lipid metabolites, phosphatidylcholines (PCs) and TAGs in various oilseed samples including Gossypium hirsutum (Horn et al ., , ), Camelina sativa (Horn et al ., ; Marmon et al ., ; Usher et al ., ), and Arabidopsis thaliana (Sturtevant et al ., ). In a particularly relevant example, the examination of developing B .…”

Properties and Biotechnological Applications of Acyl‐CoA:diacylglycerol Acyltransferase and Phospholipid:diacylglycerol Acyltransferase from Terrestrial Plants and Microalgae

“…decreased linoleic acid content) in many transgenic lines, supporting the contribution of PDAT1 in seed oil biosynthesis. Consistently, microRNA‐mediated downregulation of PDAT1 in C. sativa led to a decrease in the linoleic acid content, whereas overexpression of PDAT1 had an opposite effect (Marmon et al, ). The changes in fatty‐acid composition in these PDAT1 overexpression or downregulation lines, however, were not accompanied by any significant effects on the total oil content.…”