Abstract
The aerial organs of most terrestrial plants are covered by a hydrophobic protective cuticle. The main constituent of the cuticle is the lipid polyester cutin, which is composed of aliphatic and aromatic domains. The aliphatic component is a polyester between fatty acid/alcohol and hydroxycinnamoyl acid. The BAHD/HxxxD family enzymes are central to the synthesis of these polyesters. The nature of this class of enzymes in bryophytes has not been explored to date. Here, a gene encoding a fatty ω-hydroxyacid/fatty alcohol hydroxycinnamoyl transferase (HFT) has been isolated from the liverwort Marchantia emarginata and has been functionally characterized. Experiments based on recombinant protein showed that the enzyme uses ω-hydroxy fatty acids or primary alcohols as its acyl acceptor and various hydroxycinnamoyl-CoAs—preferentially feruloyl-CoA and caffeoyl-CoA—as acyl donors at least in vitro. The transient expression of a MeHFT-GFP fusion transgene in the Nicotiana benthamiana leaf demonstrated that MeHFT is directed to the cytoplasm, suggesting that the feruloylation of cutin monomers takes place there.
Highlights
The evolution of plants from marine/aquatic to terrestrial organisms has necessitated the development of a protective outer coat, primarily to prevent water loss [1,2,3]
Experiments based on recombinant protein showed that the enzyme uses ω-hydroxy fatty acids or primary alcohols as its acyl acceptor and various hydroxycinnamoyl-CoAs—preferentially feruloyl-CoA and caffeoyl-CoA—as acyl donors at least in vitro
Cutin has a high content of the C16 fatty acid ferulic acid and the C18 fatty acid p-coumaric acid linked by esterification to glycerol [1,5,6]
Summary
The evolution of plants from marine/aquatic to terrestrial organisms has necessitated the development of a protective outer coat, primarily to prevent water loss [1,2,3]. Three functional classes of these enzymes have been identified, namely the alcohol acetyltransferases [11,12,13], the anthocyanin/flavonoid acyltransferases [14,15,16,17,18] and the hydroxycinnamoyl transferases [19,20,21]. Their molecular masses range from 48 to 55 kDa [10]. The enzyme hydroxycinnamoyl-CoA:ω-hydroxyacid/fatty alcohol transferase (HHT) catalyzes the formation of aromatic esters in lipidic polymers. The enzyme appears to be involved in the formation of alkyl hydroxycinnamate esters and is active in the cytoplasm; in vitro, the enzyme can use either feruloyl or caffeoyl-CoA as its acyl donor, and ω-hydroxyacids or fatty alcohols as its acyl acceptor
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