Necrosis- and Ethylene-inducing Peptide from Fusarium Oxysporum Induces a Complex Cascade of Transcripts Associated with Signal Transduction and Cell Death in Arabidopsis

Treatment of Arabidopsis (Arabidopsis thaliana) with a necrosis- and ethylene-inducing peptide (Nep1) from Fusarium oxysporum inhibited both root and cotyledon growth and triggered cell death, thereby generating necrotic spots. Nep1-like proteins are produced by divergent microbes, many of which are plant pathogens. Nep1 in the plant was localized to the cell wall and cytosol based on immunolocalization results. The ratio of chlorophyll a fluorescence (F685 nm/F730 nm) significantly decreased after 75-min treatment with Nep1 in comparison to the control. This suggested that a short-term compensation of photosynthesis occurred in response to localized damage to cells. The concentrations of most water-soluble metabolites analyzed were reduced in Arabidopsis seedlings after 6 h of Nep1 treatment, indicating that the integrity of cellular membranes had failed. Microarray results showed that short-term treatment with Nep1 altered expression of numerous genes encoding proteins putatively localized to organelles, especially the chloroplast and mitochondria. Short-term treatment with Nep1 induced multiple classes of genes involved in reactive oxygen species production, signal transduction, ethylene biosynthesis, membrane modification, apoptosis, and stress. Quantitative PCR was used to confirm the induction of genes localized in the chloroplast, mitochondria, and plasma membrane, and genes responsive to calcium/calmodulin complexes, ethylene, jasmonate, ethylene biosynthesis, WRKY, and cell death. The majority of Nep1-induced genes has been associated with general stress responses but has not been critically linked to resistance to plant disease. These results are consistent with Nep1 facilitating cell death as a component of diseases caused by necrotrophic plant pathogens.