## 1 Introduction
Almost all WRKY proteins can recognize and bind to W-box cis-elements [(T)TGAC(C/T)] in the promoter region of their target genes and can act as transcriptional activators or repressors in regulatory cascades [19,24,25]. Previous studies demonstrated that WRKY transcription factors (TFs) play an important role in multiple physiological activities, including plant growth and development, senescence, biotic and abiotic stress responses, secondary metabolism, and phytohormone signaling [26, 27, 28, 29]. Previous research shown that _AtWRKY75_ is a negative regulator of root hair development, the number and length of root hairs showed an increase in its knockout mutant compared with the wild type [30]. Knockout of the _AtWRKY41_ mutant significantly downregulated abscisic acid insensitive 3 (ABI3) and influenced the seed dormancy, through binding to three adjacent W-boxes in the promoter of the ABI3 [31]. _Hylocereus polyrhizus WRKY3_ (_HpWRKY3_) was associated with sugar accumulation of pitaya fruit by activating the transcriptions of sucrose metabolic genes [32]. In another study, overexpression of _Salvia militorhiza WRKY1_ (_SmWRKY1_) increased five-fold the tanshinone production in transgenic lines through binding to the W-box elements of the promoter 1-deoxy-p-xylulose-5-phosphate reductoisomerase (_SmDXR_) involved in the methylerythitol phosphate (MEP) pathway [33]. Overexpression of _SIWRKY45_ enhanced tomato susceptibility to the root-knot nematode _Meloidogyne javanica_, which was associated with decreased expression of salicylic acid (SA) and jasmonic acid (JA) marker genes [34]. In addition, _PbrVRKY53_ gene of _Pyrus betulafolia_ positively regulated the enhanced tolerance to drought stress by regulating _PbrNCED1_ expression [35]. So far, from all these previous studies, it may conclude that WRKY proteins play important roles in multiple physiological activities. However, the functions of some _WRKY_ genes, particularly in \(O\)_pumila_, still remain unexplored. Here, in this study, a novel gene _OpWRKY3_ encoding for WRKY transcription factor was isolated from _O. pumila_ and functionally characterized. OpWRKY3 shared high homology with VvWRKY30, VqWRKY52, PtWRKY30, AcWRKY41, and AtWRKY30. OpWRKY3 possessed one WRKY domain and a C2 HC motif and was classified into group III. The biomass of repression _OpWRKY3_ transgenic hairy roots was significantly reduced by suppressing the growth and development of root tip. While there were slight changes observed in _OpWRKY3_-overexpressing lines. In addition, overexpression of _OpWRKY3_ in hairy roots resulted in increased concentration and total production (hairy roots and medium) of loganin and decrease of secologanin contentration and production in hairy roots, while repression of _OpWRKY3_ resulted in opposite effect compared with the overexpressed lines. The overexpression of _OpWRKY3_ resulted in increased the total production of CPT while repression of _OpWRKY3_ suppressed significantly the CPT production. Thus, the findings of this study will serve as an accentuating reference for future research on the regulators of alkaloid production in various medicinal plants.