The Unique Role of the ECERIFERUM2-LIKE Clade of the BAHD Acyltransferase Superfamily in Cuticular Wax Metabolism

Abstract

The elongation of very-long-chain fatty acids is a conserved process used for the production of many metabolites, including plant cuticular waxes. The elongation of precursors of the most abundant cuticular wax components of some plants, however, is unique in requiring ECERIFERUM2-LIKE (CER2-LIKE) proteins. CER2-LIKEs are a clade within the BAHD superfamily of acyltransferases. They are known to be required for cuticular wax production in both Arabidopsis and maize based on mutant studies. Heterologous expression of Arabidopsis and rice CER2-LIKEs in Saccharomyces cerevisiae has demonstrated that they modify the chain-length specificity of elongation when paired with particular condensing enzymes. Despite sequence homology, CER2-LIKEs are distinct from the BAHD superfamily in that they do not appear to use acyl transfer activity to fulfill their biological function. Here, we review the discovery and characterization of CER2-LIKEs, propose several models to explain their function, and explore the importance of CER2-LIKE proteins for the evolution of plant cuticles.

Cuticular Waxes of Arabidopsis thaliana Shoots: Cell-Type-Specific Composition and Biosynthesis

“…Based on Arabidopsis ksc mutant analyses, the KCS enzyme KCS6/CER6 was found to be central for cuticular wax biosynthesis, as it elongates C 24 to C 28 acyl-CoAs. More recently, it was shown that the KCS6/CER6 FAE complex may be associated with CER2-LIKE proteins, then enabling elongation of acyl-CoAs up to C 34 ( Figure 3 ), yet the mechanism of action of CER2-LIKE proteins remains unknown [ 22 , 23 , 24 , 25 ].…”

Single nuclei transcriptome of the Lesser Duckweed Lemna minuta reveals cell trajectories for an entire plant

“…5B and 7). The frond epidermal cells were defined by the marker gene ECERIFERUM-like , which has been shown to be important for cuticle wax development (Haslam et al, 2017). Additional markers include an auxin efflux carrier in starch metabolising cells PIN-FORMED (PIN7) aiding root termination (Kim et al, 2013; Rosquete and Kleine-Vehn, 2018).…”

The Polyketide Components of Waxes and the Cer-cqu Gene Cluster Encoding a Novel Polyketide Synthase, the β-Diketone Synthase, DKS

“…Two important facets must be kept in mind when contemplating this question. Firstly, the ubiquitous KCS elongation systems require At CER-22-like proteins for the final elongation steps [ 57 ]. When these genes are mutated, shorter chain lengths are present in the wax.…”

“… What genes determine the deduced thioesterase, decarboxylase, methylketone reductase, and ester synthase enzymes in the alkan-2-ol ester branch pathway? Why are AtCER2 orthologs, that are required for the final KCS elongation steps of ubiquitous wax aliphatics [ 57 ], apparently not required for the final elongations in synthesis of the β-diketone aliphatics? What are the roles of the barley Cer-a , - b , - x and - yl loci products in eliminating almost all or all synthesis of polyketide wax aliphatics, and simultaneously modifying synthesis of ubiquitous wax aliphatics?…”

“…Why are AtCER2 orthologs, that are required for the final KCS elongation steps of ubiquitous wax aliphatics [ 57 ], apparently not required for the final elongations in synthesis of the β-diketone aliphatics?…”