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

Abstract

The plant <i>Ophiorrhiza pumila</i> 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 <i>OpWRKY3</i> was isolated from <i>O. pumila</i>, 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. <i>OpWRKY3</i> was responsive to various treatments, including gibberellin (GA₃), methyl jasmonate (MJ), acetylsalicylic acid (ASA), salicylic acid (SA), and abscisic acid (ABA). Besides, <i>OpWRKY3</i> is expressed predominantly in stems. Subcellular localization analysis showed that OpWRKY3 localized in the nucleus. The biomass of <i>OpWRKY3-SRDX</i> transgenic hairy roots (S line) was visibly suppressed, while there were slight changes between overexpression of the <i>OpWRKY3</i> 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 <i>OpWRKY3</i> may act as a regulator in the growth and development of <i>O. pumila</i>, and in production of camptothecin and its precursors.