Harpin protein induces disease resistance in diverse plant species. Transcriptome study of tomato (Solanum lycopersicum) genome indicated that harpin activated cellular events of transcription regulation, signaling transduction, stress response, membrane transporting, photosynthesis and cell wall biosynthesis. Among the harpin-induced genes, the expression of tomato ethylene-response factor 5 (designated as SIERF5) was induced to the highest level. The amino acid sequence of SIERF5 was closely related to that of CaEREBP-C4, NtERF4 and NsERF4. Overexpression of SIERF5 in Arabidopsis thaliana activated a large number of genes involved in signaling pathways of disease resistance, redox system, abiotic response and protein phosphorylation. Seedlings of transgenic plants exhibited hypersensitive response to exogenous ABA and increased tolerance to salt stress. In summary, the results of this study suggest that SIERF5 is a transcription activator for genes involved in the responses to ABA. biotic and abiotic stress. Thus, harpin may exert its effect on plant growth and defense response through activation of SIERF5 transcription factors. (C) 2010 Elsevier Inc. All rights reserved.