Regulation and signal transduction of sweet potato IbWIPK in wounding response

Sporamin is a storage protein of tuberous root with trypsin inhibitory activity in sweet potato. It has been reported that IbNAC1 transcription factor can upregulate sporamin expression in sweet potato leaves upon wounding, and enhance resistant ability against herbivory. Previously, a MAPK family protein, IbWIPK, has been identified as a wound-inducible activator for IbNAC1 and sporamin expression. However the wound-regulatory mechanism of IbWIPK expression is still unclear. In this study, the 884-bp of IbWIPK promoter region was cloned and analyzed. In the promoter activity analysis, we found that TGACG-motif is important in the activation of IbWIPK promoter in response to wounding. A combination of DNA/protein interaction resulted that a bZIP transcription factor, IbTGA1a, was screened to bind to and activate TGACG-motif. Furthermore, the expression of IbTGA1a was induced faster than IbWIPK after wounding. These results suggested that IbTGA1a is the upstream activator of IbWIPK. Additionally, two bHLH transcription factors, IbbHLH3 and IbbHLH4, and one IbEIL1 were found to interact with IbWIPK by yeast-two hybrid assays, suggesting that IbWIPK might modulate JA response and ethylene response by interaction and phosphorylation of these target proteins. Collectively, this study proposes a signal transduction pathway of IbWIPK expression during wounding stress, and it regulates the hormone responses by protein interaction and phosphorylation in sweet potato leaves.