Frontiers in Plant Science (Sep 2016)
A novel class of plant type III polyketide synthase involved in orsellinic acid biosynthesis from Rhododendron dauricum
Abstract
Rhododendron dauricum L. produces daurichromenic acid, the anti-HIV meroterpenoid consisting of sesquiterpene and orsellinic acid moieties. To characterize the enzyme responsible for orsellinic acid biosynthesis, a cDNA encoding a novel polyketide synthase, orcinol synthase (ORS), was cloned from young leaves of R. dauricum. The primary structure of ORS shared relatively low identities to those of polyketide synthases from other plants, and the active site of ORS had a unique amino acid composition. The bacterially expressed, recombinant ORS accepted acetyl-CoA as the preferable starter substrate, and produced orcinol as the major reaction product, along with four minor products including orsellinic acid. The ORS identified in this study is the first plant polyketide synthase that generates acetate-derived aromatic tetraketides, such as orcinol and orsellinic acid. Interestingly, orsellinic acid production was clearly enhanced in the presence of Cannabis sativa olivetolic acid cyclase, suggesting that the ORS is involved in orsellinic acid biosynthesis together with an unidentified cyclase in R. dauricum.
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