ABSTRACT

Cholinesterase is consisting of acetylcholinesterase (AChE) and pseudocholinesterase in vertebrates and invertebrates. AChE 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 AChE gene paralog encodes propionylcholinesterase (PChE), a pseudocholinesterase in rice. PChE was found to be located adjacent to AChE (Os07g0586200) on rice chromosome 7 and designated as Os07g0586100. Phylogenetic tree analysis showed a close relationship between rice AChE and PChE. PChE-overexpressing rice had higher hydrolytic activity toward propionylthiocholine than acetylthiocholine and showed extremely low activity against butyrylthiocholine. Therefore, the PChE 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 PChE in plants.

摘要

胆碱酯酶由脊椎动物和无脊椎动物中的乙酰胆碱酯酶 (AChE) 和假胆碱酯酶组成。AChE基因已在几种植物物种中发现，而假胆碱酯酶基因尚未在任何植物物种中发现。在这项研究中，我们报告了AChE基因旁系同源物编码丙酰胆碱酯酶 (PChE)，这是一种水稻中的假胆碱酯酶。发现PChE位于水稻 7 号染色体上的AChE (Os07g0586200) 附近，命名为 Os07g0586100。系统发育树分析表明水稻AChE和PChE之间有密切的关系。PChE-过表达水稻对丙酰硫代胆碱的水解活性高于乙酰硫代胆碱，而对丁酰硫代胆碱的水解活性极低。因此，PChE基因产物被表征为丙酰胆碱酯酶，一种假胆碱酯酶。水稻 PChE 对胆碱酯酶抑制剂新斯的明溴化物的敏感性低于电鳗、玉米和水稻 AChE。重组 PChE 作为 171 kDa 同型四聚体发挥作用。PChE 在发育后期表达，发现其定位于水稻叶组织的细胞外空间。这些结果表明水稻植物具有 PChE，其在发育后期在细胞外空间中起作用。据我们所知，这项研究提供了植物中PChE的第一个直接证据和分子特征。