Metabolic engineering of fatty acid biosynthetic pathway in sesame (Sesamum indicum L.): assembling tools to develop nutritionally desirable sesame seed oil

Abstract

Vegetable oils are an essential component of human diet, in terms of their health beneficial roles. Despite their importance, the fatty acid profile of most commonly used edible oil seed crop plants are imbalanced; this skewed ratio of fatty acids in the diet has been shown to be a major reason for the occurrence of cardiovascular and autoimmune diseases. Until recently, it was not possible to exert significant control over the fatty acid composition of vegetable oils derived from different plants. However, the advent of metabolic engineering, knowledge of the genetic networks and regulatory hierarchies in plants have offered novel opportunities to tailor-made the composition of vegetable oils for their optimization in regard to food functionality and dietary requirements. Sesame (Sesamum indicum L.) is one of the ancient oilseed crop in Indian subcontinent but its seed oil is devoid of balanced proportion of x-6:x-3 fatty acids. A recent study by our group has shed new lights on metabolic engineering strategies for the purpose of nutritional improvement of sesame seed oil to divert the carbon flux from the production of linoleic acid (C18:2) to a-linolenic acid (C18:3). Apart from that, this review evaluates current understanding of regulation of fatty acid biosynthetic pathways in sesame and attempts to identify the major options of metabolic engineering to produce superior sesame seed oil.Keywords 1,2-sn-diacylglycerol acyltransferase Á Fatty acid desaturase Á Fatty acyl-ACP thioesterase Á Sesame seed oil Á Stearoyl-acyl-carrier protein D9-desaturase Abbreviations ACCase Acetyl Co-A carboxylase ADP Adenosine diphosphate ATP Adenosine triphosphate CVD Cardiovascular diseases DAG 1,2-diacylglycerol DGAT 1,2-sn-diacylglycerol acyltransferase ER Endoplasmic reticulum FA Fatty acid FAD3 Fatty acid desaturase-3 FAD7 Fatty acid desaturase-7 FAE Fatty acid elongase FAS Fatty acid synthase

Occurrence of plastidial triacylglycerol synthesis and the potential regulatory role of AGPAT in the model diatom Phaeodactylum tricornutum

“…The elevated production of PUFAs such as C20:4 and C20:5 in the study could be due to the elevated supply of fatty acid precursors by overexpressed PtAGPAT. Bhunia et al [ 38 ] reported that the content of fatty acids such as C20:4 and C20:5 were significantly influenced by the availability of precursor molecules. Fatty acids synthesized in the chloroplast were transported to cytosol where CoA was attached by long-chain fatty acyl-CoA synthetase and subsequent for esterification.…”

The FAD2 Gene in Plants: Occurrence, Regulation, and Role

“…The FAD3 is a microsomal enzyme located in the ER facing the cytosol, whereas FAD7 and FAD8 are plastidial enzymes located in the inner membrane of the chloroplast envelope. In addition, FAD7 can also be found in the thylakoid of the chloroplasts ( Andreu et al, 2007 ; Bhunia et al, 2016 ). In contrast to this, FAD4 and FAD5 produce C16:1 from C16:0 in particular for phosphatidyl glycerol and mono-galactosyldiacylglycerols (MGDG), respectively ( Murphy and Piffanelli, 1998 ).…”

“… General biosynthetic pathway of fatty acids and lipids in plants [PC phosphocholine; FAD fatty acid desaturase: KAS ketoacyl-ACP synthase] ( Guan et al, 2012c : Suresha et al, 2012 ; Bhunia et al, 2016 ). …”

“…The acyl-CoA pool undergoes several modifications regarding elongation, desaturation and exchange, catalyzed by a different ER membrane bound proteins, which constitute the eukaryotic pathway of lipid biosynthesis. In the ER, C18:1-CoA is incorporated into membrane phosphatidylcholine (PC) and desaturated to C18:2-PC by the ω-6 fatty acid desaturase (FAD2), and then C18:2-PC is desaturated to C18:3-PC by the ω-3 fatty acid desaturase (FAD3) ( Bhunia et al, 2016 ). The first acylation reaction catalyzed by a glycerol-3-phosphate acyltransferase (GPAT) yields lysophosphatidic acid (LPA), which is further acylated by a lysophosphatidic acid acyltransferase (LPAAT) to the phosphatidic acid (PA).…”

“…The desaturation of stearic acid (C18:0) to oleic acid (C18:1) is catalyzed by stearoyl-acyl carrier protein desaturase (SAD). Further desaturation of oleic acid to linoleic acid (18:2) is catalyzed by FAD2 in the ER and FAD6 in the plastid, whereas linoleic acid desaturation to γ-linolenic acid (C18:3, n6) is catalyzed by FAD3 in the ER and FAD7/FAD8 in the plastid ( Zhang et al, 2012 ; Bhunia et al, 2016 ).…”