Enhanced neutraceutical serotonin derivatives of rice seed by hydroxycinnamoyl-CoA:serotonin N-(hydroxycinnamoyl)transferase

Serotonin derivatives such as p-coumaroylserotonin and feruloylserotonin, a family of plant polyphenol compounds, have been implicated in an array of biological activities including antioxidative activity, but neither their production nor identification has been reported in crop plants. Here, we report the detection and enhanced synthesis of serotonin derivatives in rice seeds. We identified that wild-type rice seeds synthesized a basal levels of serotonin derivatives with around 30 ng g−1 seed weight. However, transgenic rice expressing the pepper hydroxycinnamoyl-CoA:serotonin N-(hydroxycinnamoyl)transferase (SHT) produced on average 274 ng g−1 seed weight which was nine-fold higher than wild-type. In addition, production of serotonin derivatives increased upon chemical treatments such as trans-cinnamic acid and tyramine in both wild-type and transgenic rice by two- to three-fold. The DPPH radical scavenging activities of transgenic rice were higher than that of wild-type and showed concentration dependent of serotonin derivatives. These results demonstrate that overexpression of SHT provides the feasibility of engineering increased neutraceutical serotonin derivative levels in plants using this gene.