Discovery of WRKY transcription factors through transcriptome analysis and characterization of a novel methyl jasmonate-inducible PqWRKY1 gene from Panax quinquefolius

Transcription factors (TFs) are important regulating factors that can mediate many life processes. However, no TF genes have previously been reported in Panax quinquefolius (American ginseng), with the exception of a few expressed sequence tags. In this study, 753 unigenes (unique sequences) have been annotated in the plant transcription factor database PlnTFDB (version 3.0) by mining a 454 transcriptome dataset of P. quinquefolius. After classification of the unigenes, 45 unigenes were discovered to be annotated as WRKY transcripts in the public databases. Furthermore, PqWRKY1, one of the WRKY family TF genes that respond to methyl jasmonate, was isolated according to the sequences in the 454 transcriptome dataset. The cDNA of PqWRKY1 (P. quinquefolius WRKY1) encodes a putative protein of 358 amino acids, including a WRKY domain and a zinc finger motif. A subcellular localization assay demonstrated that the protein localizes to the nucleus and has strong transcriptional activation activity in transgenic yeast. In comparison to control lines, the PqWRKY1 transgenic Arabidopsis line exhibited insensitive phenotypes when exposed to high salt or mannitol. Correspondingly, in transgenic Arabidopsis lines, the expression levels of some genes involved in the anti-stress process were relatively higher than those in the control lines. Additionally, genes involved in triterpene biosynthesis were expressed onefold to fivefold higher in the transgenic line compared to the control line. These results suggest that the transcription factor PqWRKY1 is a positive regulator related to osmotic stress and triterpene ginsenoside biosynthesis in P. quinquefolius.