Very‐long‐chain fatty acid biosynthesis is controlled through the expression and specificity of the condensing enzyme

Abstract

SummaryThe Arabidopsis FATTY ACID ELONGATION1 (FAE1) gene encodes a putative seed-specific condensing enzyme. It is the first of four enzyme activities that comprise the microsomal fatty acid elongase (FAE) involved in the biosynthesis of very-long-chain fatty acids (VLCFAs). FAEI has been expressed in yeast and in tissues of Arabidopsis and tobacco, where significant quantities of VLCFAs are not found. The introduction of FAE1 alone in these systems is sufficient for the production of VLCFAs, for wherever FAE1 was expressed, VLCFAs accumulated. These results indicate that FAE1 is the rate-limiting enzyme for VLCFA biosynthesis in Arabidopsis seed, because introduction of extra copies of FAE1 resulted in higher levels of the VLCFAs. Furthermore, the condensing enzyme is the activity of the elongase that determines the acyl chain length of the VLCFAs produced. In contrast, it appears that the other three enzyme activities of the elongase are found ubiquitously throughout the plant, are not rate-limiting and play no role in the control of VLCFA synthesis. The ability of yeast containing FAE1 to synthesize VLCFAs suggests that the expression and the acyl chain length specificity of the condensing enzyme, along with the apparent broad specificities of the other three FAE activities, may be a universal eukaryotic mechanism for regulating the amounts and acyl chain length of VLCFAs synthesized.

Expression of the Isochrysis C18-Δ9 Polyunsaturated Fatty Acid Specific Elongase Component Alters Arabidopsis Glycerolipid Profiles

“…The condensation reaction catalyzed by a substrate-specific condensing enzyme is considered to be rate limiting; hence, FAE1 most probably encodes the condensing component (Kunst et al, 1992;Millar and Kunst, 1997).…”

Disruption of Glycosylphosphatidylinositol-Anchored Lipid Transfer Protein Gene Altered Cuticular Lipid Composition, Increased Plastoglobules, and Enhanced Susceptibility to Infection by the Fungal Pathogen Alternaria brassicicola

“…During this process, the C16 and C18 fatty acids synthesized in the plastids are exported to the cytosol, where they are further elongated to VLCFAs in the range of 20 to 34 carbons by the fatty acid elongase complex on the endoplasmic reticulum (ER; Millar and Kunst, 1997;Millar et al, 1999;Todd et al, 1999;Yephremov et al, 1999;Fiebig et al, 2000;Clemens and Kunst, 2001;Hooker et al, 2002;Dietrich et al, 2005;Zheng et al, 2005). The elongated VLCFAs are then further transformed by two principal wax biosynthetic pathways: an acyl reduction pathway that produces primary alcohols and wax esters, and a decarbonylation pathway that leads to the formation of aldehydes, alkanes, secondary alcohols, and ketones (Aarts et al, 1995;Kunst and Samuels, 2003;Rowland et al, 2006).…”

Salt Induction of Fatty Acid Elongase and Membrane Lipid Modifications in the Extreme Halotolerant Alga Dunaliella salina

“…A cloned cDNA for a salt-inducible gene was found to encode the microsomal enzyme ␤-ketoacyl-CoA synthase (Kcs) that catalyzes the condensation of acyl-CoAs with malonyl-CoA to yield ␤-ketoacyl-CoA and CO 2 . This reaction is the first and rate-limiting of four reactions leading to fatty acid elongation by sequential addition of C2 units to acyls of at least C12 (Lessire et al, 1989;Millar and Kunst, 1997). The primary substrates for elongation are the products of de novo fatty acid biosynthesis in the plastid that employs the acyl carrier protein, rather than CoA, as acyl carrier.…”