Two Arabidopsis 3‐ketoacyl CoA synthase genes, KCS20 and KCS2/DAISY, are functionally redundant in cuticular wax and root suberin biosynthesis, but differentially controlled by osmotic stress

Abstract

SUMMARYVery-long-chain fatty acids (VLCFAs) are essential precursors of cuticular waxes and aliphatic suberins in roots. The first committed step in VLCFA biosynthesis is condensation of C 2 units to an acyl CoA by 3-ketoacyl CoA synthase (KCS). In this study, two KCS genes, KCS20 and KCS2/DAISY, that showed higher expression in stem epidermal peels than in stems were isolated. The relative expression of KCS20 and KCS2/DAISY transcripts was compared among various Arabidopsis organs or tissues and under various stress conditions, including osmotic stress. Although the cuticular waxes were not significantly altered in the kcs20 and kcs2/daisy-1 single mutants, the kcs20 kcs2/daisy-1 double mutant had a glossy green appearance due to a significant reduction of the amount of epicuticular wax crystals on the stems and siliques. Complete loss of KCS20 and KCS2/DAISY decreased the total wax content in stems and leaves by 20% and 15%, respectively, and an increase of 10-34% was observed in transgenic leaves that over-expressed KCS20 or KCS2/DAISY. The stem wax phenotype of the double mutant was rescued by expression of KSC20. In addition, the kcs20 kcs2/daisy-1 roots exhibited growth retardation and abnormal lamellation of the suberin layer in the endodermis. When compared with the single mutants, the roots of kcs20 kcs2/daisy-1 double mutantss exhibited significant reduction of C 22 and C 24 VLCFA derivatives but accumulation of C 20 VLCFA derivatives in aliphatic suberin. Taken together, these findings indicate that KCS20 and KCS2/DAISY are functionally redundant in the two-carbon elongation to C 22 VLCFA that is required for cuticular wax and root suberin biosynthesis. However, their expression is differentially controlled under osmotic stress conditions. Keywords: Arabidopsis thaliana, 3-ketoacyl CoA synthase, suberin, very-long-chain fatty acids (VLCFAs), wax. INTRODUCTIONVery-long-chain fatty acids (VLCFAs) are fatty acids with chains of 20 or more carbons. In plants, VLCFAs are essential precursors of various lipids, including the cuticular waxes that cover the aerial surfaces (for review, see Jenks et al., 1994;Post-Beittenmiller, 1996;Kunst and Samuels, 2003;Samuels et al., 2008), the aliphatic suberin embedded in the cell walls of the root endodermis and the periderm of shoots and roots (for review, see Kolattukudy, 1980Kolattukudy, , 2001Bernards, 2002;Franke and Schreiber, 2007;Pollard et al., 2008), the triacylglycerols (TAGs) that accumulate in seeds (Stefansson et al., 1961;Lassner et al., 1996;Barret et al., 1998), and the sphingolipids and phospholipids in cell membranes (Schneiter et al., 1996;Devaiah et al., 2006;Dickson et al., 2006). VLCFA derivatives act as protective barriers between plants and the environment, provide energy storage in seeds, and function as signaling molecules in membranes.Cuticular waxes are mainly composed of complex mixtures of VLCFAs and their derivatives, aldehydes, alkanes, primary In higher plants, root suberin is organized in a characteristic lamella structure that conta...

Apoplastic Diffusion Barriers in Arabidopsis

“…For example, localized suberization is modified in response to drought, salinity or wounding. Consistent with these observations, the suberin biosynthetic genes are transcriptionally activated by the same environmental factors Lee et al, 2009;Domergue et al, 2010). The BDG, LACS2 and PEC1 genes that are involved in cutin deposition are also transcriptionally upregulated by drought and abscisic acid Cuticle formation is regulated during organ development and by environmental factors.…”

“…In Arabidopsis, the initial step of FAE is catalyzed by 21 members of the 3-keto acyl-CoA synthase (KCS) family. The enzymes encoded by KCS2/DAISY (At1g04220) and KCS20 (At5g43760) have been demonstrated to be involved in the production of >C20 suberin constituents Lee et al, 2009). The moderate chemical phenotypes and the substantial amounts of very long-chain suberin monomers observed in these mutants indicate the participation of one or more additional KCS enzymes in suberin biosynthesis.…”

Exploiting Natural Variation to Uncover an Alkene Biosynthetic Enzyme in Poplar

“…PotriKCS1 and 2 fall into the same clade as Arabidopsis KCS2 and 20, two condensing enzymes that have been reported to produce predominantly saturated VLCFAs up to 26 carbons in length and are implicated in suberin biosynthesis in roots and wax formation in stems (Tresch et al, 2012;Trenkamp et al, 2004;Lee et al, 2009;Franke et al, 2009;Blacklock and Jaworski, 2006). This suggests that KCSs are very plastic enzymes, whose substrate specificity can quickly change to increase wax diversity.…”

The MYB96 Transcription Factor Regulates Cuticular Wax Biosynthesis under Drought Conditions inArabidopsis

“…A major functional category of the upregulated genes included those encoding a subset of wax biosynthetic enzymes ( Figure 1B; see Supplemental Data Set 1B online), such as KCS1, KCS2, KCS6, KCR1, ECERIFERUM1 (CER1), and CER3 (Aarts et al, 1995;Todd et al, 1999;Fiebig et al, 2000;Rowland et al, 2007;Beaudoin et al, 2009;Lee et al, 2009b). Genes encoding putative wax transporters were also upregulated in the mutant ( Figures 1B and 1C), suggesting that cuticular wax biosynthesis and transport are broadly influenced in the myb96-1D mutant.…”