The p38-like MAP kinase modulated HO accumulation in wounding signaling pathways of sweet potato.

In sweet potato (Ipomoea batatas cv Tainung 57), MAPK cascades are involved in the regulation of Ipomoelin (IPO) expression upon wounding. p38 MAPK plays an important role in plant's responses to various environmental stresses. However, the role of p38-like MAPK in wounding response is still unknown. In this study, the levels of phosphorylated-p38-like MAPK (pp38-like MAPK) in sweet potato were noticeably reduced after wounding. In addition, SB203580 (SB), a specific inhibitor blocking p38 MAPK phosphorylation, considerably decreased the accumulation of pp38-like MAPK. Expression of a wound-inducible gene IPO was elevated by SB. Moreover, it stimulated hydrogen peroxide (HO) production rather than cytosolic Ca elevation in sweet potato leaves. However, NADPH oxidase (NOX) inhibitor diphenyleneiodonium could not inhibit IPO induction stimulated by SB. These results indicated a p38-like MAPK mechanism was involved in the regulation of IPO expression through NOX-independent HO generation. In addition, the presence of the protein phosphatase inhibitor okadaic acid or the MEK1/ERK inhibitor PD98059 repressed the HO- or SB-induced IPO expression, demonstrating phosphatase(s) and MEK1/ERK functioning in the downstream of HO and pp38-like MAPK in the signal transduction pathway stimulating IPO. Conclusively, wounding decreased the amount of pp38-like MAPK, stimulated HO production, and then induced IPO expression.