Rhododendron dauricum L. produces daurichromenic acid, the anti-HIV meroterpenoid consisting of sesquiterpene and orsellinic acid (OSA) moieties. To characterize the enzyme responsible for OSA biosynthesis, a cDNA encoding a novel polyketide synthase (PKS), orcinol synthase (ORS), was cloned from young leaves of R. dauricum. The primary structure of ORS shared relatively low identities to those of PKSs 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 OSA. The ORS identified in this study is the first plant PKS that generates acetate-derived aromatic tetraketides, such as orcinol and OSA. Interestingly, OSA production was clearly enhanced in the presence of Cannabis sativa olivetolic acid cyclase, suggesting that the ORS is involved in OSA biosynthesis together with an unidentified cyclase in R. dauricum.

Rhododendron dauricum produces daurichromenic acid, an anti-HIV meroterpenoid, via oxidative cyclization of the farnesyl group of grifolic acid. The prenyltransferase (PT) that synthesizes grifolic acid is a farnesyltransferase in plant specialized metabolism. In this study, we demonstrated that the isoprenoid moiety of grifolic acid is derived from the 2-C-methyl-d-erythritol-4-phosphate pathway that takes place in plastids. We explored candidate sequences of plastid-localized PT homologs and identified a cDNA for this PT, RdPT1, which shares moderate sequence similarity with known aromatic PTs. RdPT1 is expressed exclusively in the glandular scales, where daurichromenic acid accumulates. In addition, the gene product was targeted to plastids in plant cells. The recombinant RdPT1 regiospecifically synthesized grifolic acid from orsellinic acid and farnesyl diphosphate, demonstrating that RdPT1 is the farnesyltransferase involved in daurichromenic acid biosynthesis. This enzyme strictly preferred orsellinic acid as a prenyl acceptor, whereas it had a relaxed specificity for prenyl donor structures, also accepting geranyl and geranylgeranyl diphosphates with modest efficiency to synthesize prenyl chain analogs of grifolic acid. Such a broad specificity is a unique catalytic feature of RdPT1 that is not shared among secondary metabolic aromatic PTs in plants. We discuss the unusual substrate preference of RdPT1 using a molecular modeling approach. The biochemical properties as well as the localization of RdPT1 suggest that this enzyme produces meroterpenoids in glandular scales cooperatively with previously identified daurichromenic acid synthase, probably for chemical defense on the surface of R. dauricum plants.

The synthesis of dicarboxylic acids (DCAs) in Candida tropicalis is thought to be induced by a decrease in fatty acyl-CoA-oxidase activity. However, in the present study we demonstrate that repression of the POX4 gene, encoding fatty acyl-CoA oxidase, does not directly lead to high-level production of DCAs. No fatty acyl-CoA-oxidase activity was detected if the POX4 gene of C. tropicalis strain 1098 (wild-type strain) was disrupted. Furthermore, introduction of the POX4 gene from C. tropicalis strain M1210A3, which is a mutant derived from strain 1098 and is used as an industrial DCA-producing strain, still exhibited low-level fatty acyl-CoA-oxidase activity. Nevertheless, production of DCA was not observed in either case. Furthermore, the increase in acyl-CoA-oxidase activity by expression of the POX4 gene in strain M1210A3 did not reduce high-level production of DCA. These results suggest that alterations in acyl-CoA-oxidase activity are not necessarily related to production of DCA in industrial DCA-producing C. tropicalis M1210A3.

We evaluated the performance of a resorcinol-formaldehyde (RF) hydrogel as an adsorbent for removing aqueous cesium ions (Cs + ), by synthesizing cylindrical pellets of RF gels under different molar ratios (R/C) between resorcinol (R) and sodium carbonate (C) as the catalyst for the sol-gel polycondensation in the range from 2.5 to 400. The RF gel prepared at R/C = 2.5, containing the greatest amount of sodium ion (Na + ), had the greatest Cs + adsorption amount (0.660 mmol g −1 ), because Cs + could be adsorbed on the network structure in the gel through exchange with Na + at an equal molar ratio, but with the smallest effective diffusion coefficient of Cs + (1.45 × 10 -12 m 2 s −1 ). Kinetic analyses based on the Dryden-Kay and intra-particle diffusion models revealed that the diffusivity of Cs + in the RF gel depended strongly on the density of the network structure, which can be controlled by varying the R/C ratio.

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 Prime Archives in Plant Sciences: 2 nd Edition 3 www.videleaf.com 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.