Isolation of polyphenol oxidase genes from Portulaca oleracea and evaluation of their ability to metabolize endocrine-disrupting chemicals

Portulaca (Portulaca oleracea cv.), a garden plant, efficiently removes endocrine-disrupting chemicals (EDCs) including bisphenol A (BPA) from hydroponic solution. We hypothesized that polyphenol oxidase (PPO) was involved in the initial steps of detoxifying EDCs in portulaca roots. In order to elucidate the molecular basis of portulaca's ability to metabolize EDCs, we first isolated five PPO genes (PoPPO1-5) that were expressed mainly in portulaca roots. Among these genes, PoPPO2, PoPPO4 and PoPPO5 were introduced into cultured tobacco cells and expressed as active forms. We found that crude extracts from the cells expressing PoPPO2, PoPPO5, and to a lesser extent PoPPO4, could metabolize BPA. In addition, we found that the BPA metabolites from crude extracts of cells expressing PoPPO2, PoPPO4 and PoPPO5 were identical to those of portulaca. Moreover, PoPPO2 and PoPPO5 also caused hydroxylation of octylphenol, nonylphenol and 17 beta-estradiol. Therefore, these results strongly suggest that PoPPOs significantly contribute to the superior ability of portulaca to metabolize EDCs.