Production of pinostilbene compounds by the expression of resveratrol O-methyltransferase genes in Escherichia coli

Resveratrol (3,4′,5-trans-trihydroxystilbene) is a polyphenolic phytoalexin that belongs to a family of naturally occurring stilbenes. It has been reported that the health-promoting activities of certain methylated resveratrol derivatives are more effective than those of unmodified resveratrol. In this study, we isolated two candidate genes with resveratrol O-methyltransferase (ROMT) activity from grape (Vitis riparia) and sorghum (Sorghum bicolor). To assess their ROMT activities in vivo, we synthesized VrROMT and SbROMT3 following codon-optimization and expressed the VrROMTsyn and SbROMT3syn genes using a dual expression vector system. Furthermore, we attempted to produce pterostilbene from resveratrol as a substrate by the expression of two putative ROMT proteins in Escherichia coli. Unexpectedly, expression of the SbROMT3syn gene in E. coli led to the production of mono-methylated stilbene (3,4′-dihydroxy-5-methoxy-trans-stilbene, pinostilbene) from resveratrol compounds. However, a very small amount of di-methylated stilbene (3,5-dimethoxy-4′-hydroxy-trans-stilbene, pterostilbene) was also detected. Consistently, we found that in vitro methylation assays of resveratrol by recombinant SbROMT3syn produced pinostilbene as the major product besides a very small amount of pterostilbene. By contrast, very small amounts of methylated resveratrol derivatives were detected in E. coli expressing the VrROMTsyn protein. This suggests that the SbROMT3syn is more useful in the production of pinostilbene compounds than pterostilbene from resveratrol in E. coli.