Genome-wide identification of the WRKY gene family in Codonopsis pilosula and functional analysis of CpWRKY8 under drought stress.

Codonopsis pilosula (Franch.) Nannf., a perennial herbaceous species in the family Campanulaceae, is widely used in traditional medicine for its dried roots. Drought stress severely constrains both the yield and the accumulation of bioactive compounds in this species. In this study, we performed a genome-wide identification and phylogenetic analysis of the WRKY TF (TF) family in C. pilosula, identifying 49 members that were classified into seven subfamilies. Among them, CpWRKY8, a member of the Group IIa subfamily, localized to the nucleus and showed transcriptional activation activity in yeast. Under drought stress conditions, Nicotiana tabacum plants overexpressing (OE) CpWRKY8 exhibited greater tolerance to drought stress than wild-type (WT) N. tabacum plants, as evidenced by higher survival rates, lower malondialdehyde (MDA) levels, and higher superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities; furthermore, these physiological advantages were largely maintained following rehydration. Furthermore, yeast one-hybrid (Y1H) and dual-luciferase reporter (DLR) assays demonstrated that the abscisic acid (ABA) receptor CpPYR/PYL activated the CpWRKY8 promoter in heterologous systems. In summary, we propose a working model in which CpPYR/PYL indirectly upregulates CpWRKY8; this module enhances drought tolerance by increasing antioxidant capacity, thereby providing a theoretical basis for the molecular breeding of drought-tolerant medicinal plants.