COSY catalyses trans–cis isomerization and lactonization in the biosynthesis of coumarins

Abstract

Coumarins or 1,2-benzopyrones comprise a large class of secondary metabolites ubiquitously found in the plant kingdom. In many plant species, coumarins are particularly important for iron acquisition and plant defense. Here we show that COUMARIN SYNTHASE (COSY) is a key enzyme in the biosynthesis of coumarins. Arabidopsis thaliana cosy mutants are strongly reduced in coumarin levels and accumulate ohydroxyphenylpropanoids instead. Accordingly, cosy mutants have reduced iron content and show growth defects when grown under conditions where iron availability is limited. Recombinant COSY is able to produce umbelliferone, esculetin and scopoletin from their respective o-hydroxycinnamoyl-CoA thioesters via two reaction steps: a trans-cis isomerization followed by a lactonization. This conversion happens partially spontaneously and is catalyzed by light, which explains why the need for an enzyme for this conversion has been overlooked. The combined results show that COSY has an essential role in the biosynthesis of coumarins in organs that are shielded from light, such as roots. These findings provide routes to improving coumarin production in crops or via microbial fermentation.

Convergent evolution of the UbiA prenyltransferase family underlies the independent acquisition of furanocoumarins in plants

“…However, this enzyme might contribute to umbelliferone synthesis in other species. An in vitro experiment demonstrated that AtCOSY is able to synthesize this FC precursor from 2,4‐dihydroxycinamoyl‐CoA (Vanholme et al ., ). The homologous genes of AtCOSY are conserved in various angiosperm taxa, including FC‐rich species, that is, fig, Angelica archangelica (Apiaceae), Bituminaria bituminosa (Fabaceae) and Citrus × paradisi (Rutaceae) (Murray et al ., ) (Fig.…”

“…Recently, a new gene encoding an enzyme catalysing trans‐cis isomerization and lactonization of o ‐hydroxycinnamoyl‐CoA (Vanholme et al ., ) was reported, which serves as an alternative route to the nonenzymatic process in coumarin skeleton formation (Fig. ).…”

“…). This A. thaliana COUMARIN SYNTHASE ( COSY ) is responsible for the formation of scopoletin and esculetin (Vanholme et al ., ), neither of which is demonstrated to be incorporated into FCs in plants. However, this enzyme might contribute to umbelliferone synthesis in other species.…”

Coumarin accumulation and trafficking in Arabidopsis thaliana: a complex and dynamic process

“…Previous studies have shown that the co‐cultivation of mutants defective in coumarin biosynthesis (e.g. f6′h1‐1 , cosy‐1 and cosy‐2 ) with WT plants was sufficient to rescue the mutant phenotypes (Rodriguez‐Celma et al ., 2013; Schmidt et al ., 2014; Vanholme et al ., 2019). In addition, chemical complementation experiments for f6′h1‐1 , s8h‐1 and s8h‐2 mutants showed that exogenous provision of coumarins (i.e.…”

IRONMAN Tunes Responses to Iron Deficiency in Concert with Environmental pH

“…In the light, 6-hydroxyferuloyl-CoA is converted into scopoletin, a reaction that occurs partially spontaneous. In light-protected organs such as roots, scopoletin biosynthesis is dependent on enzymatic catalysis via COUMARIN SYNTHASE (COSY) (Vanholme et al, 2019). Similar to F6’H1, COSY activity is indispensable for growth on alkaline substrates (Vanholme et al, 2019), suggesting that compounds which are produced downstream of scopoletin are required for the mobilization of Fe.…”