WRKY transcription factor OpWRKY1 acts as a negative regulator of camptothecin biosynthesis in Ophiorrhiza pumila hairy roots

Camptothecin (CPT) has unique anti-tumor activities, and its analogs such as irinotecan and topotecan are clinically used as anti-cancer drugs. Recently, CPT biosynthesis pathway is gradually being resolved. However, few studies have been conducted on transcription factors (TFs), which regulate CPT biosynthesis in Ophiorrhiza pumila . In this study, we cloned and functionally identified a new OpWRKY1 TF from O. pumila that was preferentially expressed in stems and responded to exogenous elicitors such as gibberellin, acetylsalicylic acid, salicylic acid, abscisic acid and 1-aminocyclopropane-carboxylic acid. Subcellular localization assay showed that OpWRKY1 was specifically expressed in the nucleus. Transgenic results revealed that over-expression of OpWRKY1 significantly repressed CPT accumulation in the hairy roots by inhibiting the expression of several CPT biosynthesis genes, especially OpCPR . Furthermore, Dual-Luciferase assay and yeast-one-hybrid assay showed that OpCPR was a target of OpWRKY1. The above results elucidated how OpWRKY1 directly down-regulated the transcription of OpCPR and inhibited CPT biosynthesis in O. pumila. Our findings indicate that OpWRKY1 acts as a negative regulator of CPT biosynthesis in O. pumila and provide new insights on metabolic engineering of CPT metabolism in the future.