Induction of defense responses in tobacco by the protein Nep1 from Fusarium oxysporum

Abstract

Fusarium oxysporum produces a 24-kDa protein, Nep1, which induces necrosis and ethylene production in leaves of many dicot plant species. Detached Nicotiana tabacum L. cv. Xanthi leaves respond with concentration-dependent necrosis after infiltration with Nep1 or when Nep1 is taken up by the vascular tissue. This response follows the induction of ethylene biosynthesis and accumulation of ACC synthase and ACC oxidase transcripts. Pretreating the leaves with 100 μl/l ethylene prior to elicitation enhanced Nep1-induced ethylene production. Nep1 (208 nM) causes extensive necrosis of mature tobacco leaf tissue when applied to Xanthi tobacco as a foliar spray (129 ml/m 2). Tobacco cell cultures respond to Nep1 by alkalization of the culture media, the accumulation of potassium in the media, oxygen uptake, induction of active oxygen species, and eventual cell death. The response of cultured tobacco cells to Nep1 is time- and concentration-dependent. Cell death was the same at 300 min for 5 ng/ml and higher concentrations, while 0.5 ng/ml had no effect on cell death. In the case of O 2 uptake, cells responded to 0.5 ng/ml within minutes of treatment, but at a rate lower than 5 ng/ml. The lower concentration of Nep1 did not induce an increase in pH, K + efflux, or increasing H 2O 2 accumulation in the culture media.