The Acyl Desaturase CER17 Is Involved in Producing Wax Unsaturated Primary Alcohols and Cutin Monomers

Abstract

We report n-6 monounsaturated primary alcohols (C 26:1 , C 28:1 , and C 30:1 homologs) in the cuticular waxes of Arabidopsis (Arabidopsis thaliana) inflorescence stem, a class of wax not previously reported in Arabidopsis. The Arabidopsis cer17 mutant was completely deficient in these monounsaturated alcohols, and CER17 was found to encode a predicted ACYL-COENZYME A DESATURASE LIKE4 (ADS4). Studies of the Arabidopsis cer4 mutant and yeast variously expressing CER4 (a predicted fatty acyl-CoA reductase) with CER17/ADS4, demonstrated CER4's principal role in synthesis of these monounsaturated alcohols. Besides unsaturated alcohol deficiency, cer17 mutants exhibited a thickened and irregular cuticle ultrastructure and increased amounts of cutin monomers. Although unsaturated alcohols were absent throughout the cer17 stem, the mutation's effects on cutin monomers and cuticle ultrastructure were much more severe in distal than basal stems, consistent with observations that the CER17/ADS4 transcript was much more abundant in distal than basal stems. Furthermore, distal but not basal stems of a double mutant deficient for both CER17/ADS4 and LONG-CHAIN ACYL-COA SYNTHETASE1 produced even more cutin monomers and a thicker and more disorganized cuticle ultrastructure and higher cuticle permeability than observed for wild type or either mutant parent, indicating a dramatic genetic interaction on conversion of very long chain acyl-CoA precursors. These results provide evidence that CER17/ADS4 performs n-6 desaturation of very long chain acyl-CoAs in both distal and basal stems and has a major function associated with governing cutin monomer amounts primarily in the distal segments of the inflorescence stem. Plant cuticle coats most aerial surfaces of vascular plants and plays a major role in coordinating interactions between the plant and its environment (Rensing et al., 2008; Yeats and Rose, 2013). The cuticle is primarily composed of two lipid classes, the non-polymerized (free) cuticular waxes and the cutin polyester, both of which are synthesized by epidermal cells. Common plant wax compounds are the very long chain fatty acids (VLCFAs) and their derivatives including aldehydes, primary alcohols, alkanes, secondary alcohols, ketones, and esters (Samuels et al., 2008). As much as 4.0% of total waxes on Arabidopsis (Ara-bidopsis thaliana) inflorescence stems are composed of numerous yet unidentified wax compounds (Jenks et al., 1995). Cutin consists primarily of C 16 and C 18 fatty acid derivatives (e.g. hydroxy fatty acids and dicar-boxylic acids), which are linked by ester bonds; however , glycerol and small amounts of longer chain cutin monomers have also been reported (Pollard et al., 2008). In the past decade, there has been significant progress toward understanding the molecular mechanisms controlling the cuticular wax biosynthetic pathway based primarily on studies of wax-deficient mutants (Bernard and Joubès, 2013; Yeats and Rose, 2013). Synthesis of wax occurs in epidermal cells and begins with C 16 and C 18 lon...

Compositional and transcriptomic analysis associated with cuticle lipid production on rosette and inflorescence stem leaves in the extremophyte Thellungiella salsuginea

“…Primary alcohols are produced by the acyl reduction pathway via the CER4 acyl‐CoA reductase (Rowland et al ) and wax esters via the WS transacylase (Li et al ). A desaturated wax primary alcohol generated by CER17 was recently reported (Yang et al ). From the pathway of decarbonylation, aldehydes, hydrocarbons, secondary alcohols and ketones can be produced beginning with the reduction of VLCFAs to aldehydes in which aldehyde generating WAX2/CER3 acyl‐CoA reductase and the alkane generating CER1 aldehyde decarbonylase are involved (Aarts et al , Chen et al , Bernard et al ).…”

Update on Cuticular Wax Biosynthesis and Its Roles in Plant Disease Resistance

“…These elongated very-long-chain acyl-CoAs were then modified into alkanes by the ECERIFERUM1 (CER1)/ECERIFERUM3 (CER3)/CYTOCHROME B5 (CYTB5) complex in an alkane-forming pathway, and these very-long-chain alkanes could be further oxidized to secondary alcohols and ketones by the CYP95A family cytochrome P450 enzymes MIDCHAIN ALKANE HYDROXYLASE1 (MAH1) ( Figure 1 ) [ 59 , 60 , 61 ]. In the alcohol-forming pathway, very-long-chain acyl-CoAs were converted into the n-6 monounsaturated fatty acids by the acyl desaturase ECERIFERUM17 (CER17), which was followed by the formation of primary alcohols catalyzed by the fatty acyl-CoA reductase ECERIFERUM4 (CER4) ( Figure 1 ) [ 62 , 63 ]. In addition, the Arabidopsis WAX SYNTHASE/ACYL-COA: DIACYLGLYCEROL ACYLTRANSFERASE 1 (WSD1) catalyzed the formation of wax esters through using acyl-CoAs and primary alcohols as precursors in the alcohol-forming pathway ( Figure 1 ) [ 64 ].…”

Epigenetic Activation of Enoyl-CoA Reductase By An Acetyltransferase Complex Triggers Wheat Wax Biosynthesis

“…It is well established in model plant Arabidopsis (Arabidopsis thaliana) that cuticular wax biosynthesis begins with the esterification of CoA to the plastid-derived C 16 and C 18 fatty acids by long-chain acyl-CoA synthetase proteins in the endoplasmic reticulum (ER), and the generated C 16 and C 18 acyl-CoAs are elongated to VLC acyl-CoAs under the action of the fatty acid elongase complex and ECERIFERUM2 proteins (Xia et al, 1996;Todd et al, 1999;Fiebig et al, 2000;Hooker et al, 2002;Schnurr et al, 2004;Zheng et al, 2005;Bach et al, 2008;Beaudoin et al, 2009;Lee et al, 2009;Lü et al, 2009;Weng et al, 2010;Haslam et al, 2012;Haslam and Kunst, 2013;Kim et al, 2013;Haslam et al, 2015). The elongated VLC acyl-CoAs are then modified into aldehydes, alkanes, secondary alcohols, and ketones by an alkane-forming pathway, or into primary alcohols and wax esters by an alcoholforming pathway (Aarts et al, 1995;Millar et al, 1999;Chen et al, 2003;Rowland et al, 2006Rowland et al, , 2007Greer et al, 2007;Bourdenx et al, 2011;Bernard et al, 2012;Yang et al, 2017;Pascal et al, 2019). As a core component of fatty acid elongase complex, enoyl-CoA reductase (ECR) catalyzes the final step in the biosynthesis of VLC acyl-CoAs (Zheng et al, 2005).…”