Transcriptomics-based identification of WRKY genes and characterization of a salt and hormone-responsive PgWRKY1 gene in Panax ginseng

WRKY proteins belong to a transcription factor （TF） family and play dynamic roles in many plant pro- cesses, including plant responses to abiotic and biotic stresses, as well as secondary metabolism. However, no WRKYgene in Panax ginseng C.A. Meyer has been reported to date. In this study, a number of WRKYunigenes from methyl jasmonate （MeJA）-treated adventitious root transcriptome of this species were identified using next-generation sequencing technology. A total of 48 promising WRKYunigenes encoding WRKY proteins were obtained by eliminating wrong and incomplete open reading frame （ORF）. Phylogenetic analysis reveals 48 WRKY TFs, including 11 Group I, 36 Group II, and 1 Group II1. Moreover, one MeJA-responsive unigene designated as PgWRKY1 was cloned and characterized. It contains an entire ORF of 1077 bp and encodes a polypeptide of 358 amino acid re- sidues. The PgWRKY1 protein contains a single WRKY domain consisting of a conserved amino acid sequence motif WRKYGQK and a C2H2-type zinc-finger motif belonging to WRKY subgroup II-d. Sub- cellular localization of PgWRKY1-GFP fusion protein in onion and tobacco epidermis cells revealed that PgWRKY1 was exclusively present in the nucleus. Quantitative real-time polymerase chain reac- tion analysis demonstrated that the expression of PgWRKY1 was relatively higher in roots and lateral roots compared with leaves, stems, and seeds. Importantly, PgWRKY1 expression was significantly induced by salicylic acid, abscisic acid, and NaCI, but downregulated by MeJA treatment. These results suggested that PgWRKY1 might be a multiple stress-inducible gene responding to hormones and salt stresses.