Transcription Factor OpWRKY3 Is Involved in the Development and Biosynthesis of Camptothecin and Its Precursors in Ophiorrhiza pumila Hairy Roots.

The plant Ophiorrhiza pumila produces camptothecin (CPT), a kind of terpene indole alkaloid (TIAs) that has been widely used in treatment of cancer. Tryptophan-arginine-lysine-tyrosine (WRKY) transcription factors have been reported to play important roles in plant metabolism and development. In this study, a novel WRKY transcription factor named OpWRKY3 was isolated from O. pumila, with full-length open reading frame (ORF) of 1128 bp, encoding 375 amino acids. Phylogenetic tree analysis revealed that OpWRKY3 shared the highest homology with VvWRKY30, and it is a significant feature belonging to group III. OpWRKY3 was responsive to various treatments, including gibberellin (GA₃), methyl jasmonate (MJ), acetylsalicylic acid (ASA), salicylic acid (SA), and abscisic acid (ABA). Besides, OpWRKY3 is expressed predominantly in stems. Subcellular localization analysis showed that OpWRKY3 localized in the nucleus. The biomass of OpWRKY3-SRDX transgenic hairy roots (S line) was visibly suppressed, while there were slight changes between overexpression of the OpWRKY3 line (OE line) and the control. In addition, the concentration and total production of camptothecin precursors including loganin and secologanin were significantly changed in both OE and S lines while total production of CPT was significantly changed in most transgenic lines. Thus, the present work revealed that OpWRKY3 may act as a regulator in the growth and development of O. pumila, and in production of camptothecin and its precursors.