Sunflower (Helianthus annuus) long‐chain acyl‐coenzyme A synthetases expressed at high levels in developing seeds

Abstract

Long chain fatty acid synthetases (LACSs) activate the fatty acid chains produced by plastidial de novo biosynthesis to generate acyl-CoA derivatives, important intermediates in lipid metabolism. Oilseeds, like sunflower, accumulate high levels of triacylglycerols (TAGs) in their seeds to nourish the embryo during germination. This requires that sunflower seed endosperm supports very active glycerolipid synthesis during development. Sunflower seed plastids produce large amounts of fatty acids, which must be activated through the action of LACSs, in order to be incorporated into TAGs. We cloned two different LACS genes from developing sunflower endosperm, HaLACS1 and HaLACS2, which displayed sequence homology with Arabidopsis LACS9 and LACS8 genes, respectively. These genes were expressed at high levels in developing seeds and exhibited distinct subcellular distributions. We generated constructs in which these proteins were fused to green fluorescent protein and performed transient expression experiments in tobacco cells. The HaLACS1 protein associated with the external envelope of tobacco chloroplasts, whereas HaLACS2 was strongly bound to the endoplasmic reticulum. Finally, both proteins were overexpressed in Escherichia coli and recovered as active enzymes in the bacterial membranes. Both enzymes displayed similar substrate specificities, with a very high preference for oleic acid and weaker activity toward stearic acid. On the basis of our findings, we discuss the role of these enzymes in sunflower oil synthesis.

The composition of surface wax on trichomes of Arabidopsis thaliana differs from wax on other epidermal cells

“…To date, only LACS1, LACS2 and LACS8 have been localized to the ER (Zhao et al ., ; Pulsifer et al ., ), the sub‐cellular compartment of wax biosynthesis. However, a sunflower LACS8 homolog showed substrate specificity towards 16:0 and 18:2 fatty acids, suggesting a role in oil seed or phospholipid rather than wax biosynthesis (Aznar‐Moreno et al ., ). Overall, previous evidence therefore suggested that LACS1 and LACS2 are both involved in wax formation, possibly together with other homologs such as LACS4 (and LACS3).…”

Progress in modification of sunflower oil to expand its industrial value

“…High TAG accumulation in sunflower seed is a function of a high rate of fatty acid synthesis. This high rate of fatty acid synthesis is dependent on high efficiency of photosynthates translocation and, more importantly, high rates of key enzymes such as fatty acid synthtase, thioesterase and acyl‐CoA synthtase . Two HaLACS genes (HaLACS1 and HaLACS2) were found to be actively involved in sunflower for activation of acyl which results in the high rate of TAG accumulation in seed …”

Molecular cloning and characterization of the genes encoding a microsomal oleate Δ12 desaturase (CsFAD2) and linoleate Δ15 desaturase (CsFAD3) from Camelina sativa

“…In seeds, de novo fatty acid biosynthesis takes place in the plastids and it is catalyzed by the fatty acid synthase complex (FAS), producing palmitoyl-ACP (16:0-ACP) and stearoyl-ACP (18:0-ACP) as the final products (Pidkowitc et al, 2007), both of which can be desaturated by the soluble Δ 9 stearoyl-ACP desaturase to yield palmitoyl-ACP (16:1 Δ9 -ACP) and oleoyl-ACP (18:1 Δ9 -ACP: Shanklin and Cahoon, 1998;Rodríguez-Rodríguez et al, 2015). This pool of acyl-ACPs are hydrolysed by acyl-ACP thioesterases (Voelker et al, 1997;Rodríguez-Rodríguez et al, 2014), and the resulting free fatty acids are exported out of the plastid and esterified with coenzyme A by long-acyl-CoAsynthetases (Aznar-Moreno et al, 2014). These acyl-CoAs can be incorporated into phosphatidylcholine, and oleic acid can be further desaturated by endoplasmic reticulum desaturases to linoleic and linolenic acids (Kang et al, 2011).…”