An unusual plant triterpene synthase with predominant α‐amyrin‐producing activity identified by characterizing oxidosqualene cyclases from Malus × domestica

摘要: The pentacyclic triterpenes, in particular ursolic acid and oleanolic their derivatives, exist abundantly the plant kingdom, where they are well known for anti-inflammatory, antitumour antimicrobial properties. α-Amyrin β-amyrin precursors of acids, respectively, formed by concerted cyclization squalene epoxide a complex synthase reaction. We identified three full-length expressed sequence tag sequences cDNA libraries constructed from apple (Malus × domestica 'Royal Gala') that were likely to encode triterpene synthases. Two these essentially identical (> 99% amino similarity; MdOSC1 MdOSC3). MdOSC2 transient expression Nicotiana benthamiana leaves yeast Pichia methanolica. resulting products analysed GC GC-MS. was shown be mixed amyrin (a 5 : 1 ratio α-amyrin β-amyrin). is only so far which level produced > 80% total product is, therefore, primarily an synthase. No evident when either transiently or yeast, suggesting this putative encoded pseudogene does not express systems. Transcript analysis Royal Gala indicated genes mostly peel, much lower than MdOSC3 all tissues tested. Amyrin content undertaken LC-MS, demonstrated levels ratios differ between tissues, but true consequence activity reflected ursolic/oleanolic further triterpenoids derived them. Phylogenetic placed with other synthases and/or clustered multifunctional synthases, whereas most similar