Identification and molecular characterization of propionylcholinesterase, a novel pseudocholinesterase in rice

Cholinesterase is consisting of acetylcholinesterase (AChE) and pseudocholinesterase in vertebrates and invertebrates. <i>AChE</i> gene has been identified in several plant species, while pseudocholinesterase gene has not yet been found in any plant species. In this study, we report that the <i>AChE</i> gene paralog encodes propionylcholinesterase (PChE), a pseudocholinesterase in rice. <i>PChE</i> was found to be located adjacent to <i>AChE</i> (Os07g0586200) on rice chromosome 7 and designated as Os07g0586100. Phylogenetic tree analysis showed a close relationship between rice <i>AChE</i> and <i>PChE. PChE</i>-overexpressing rice had higher hydrolytic activity toward propionylthiocholine than acetylthiocholine and showed extremely low activity against butyrylthiocholine. Therefore, the <i>PChE</i> gene product was characterized as a propionylcholinesterase, a pseudocholinesterase. The rice PChE displayed lower sensitivity to the cholinesterase inhibitor, neostigmine bromide, than electric eel, maize, and rice AChEs. The recombinant PChE functions as a 171 kDa homotetramer. PChE was expressed during the later developmental stage, and it was found be localized in the extracellular spaces of the rice leaf tissue. These results suggest that the rice plant possesses PChE, which functions in the extracellular spaces at a later developmental stage. To the best of our knowledge, this study provides the first direct evidence and molecular characterization of <i>PChE</i> in plants.