Expressing a Citrus ortholog of Arabidopsis ERF1 enhanced cold-tolerance in tobacco

The ERF1 gene was well characterized in Arabidopsis to be responsive to salt, drought, heat and necrotrophic fungi. In this paper, an ortholog of ERFI, designated as CsERF that was isolated originally as an ethylene induced gene from Citrus sinensis (L) Osbeck, was characterized. Sequence analysis revealed that CsERF and ERF1 belonged to the same AP2/ERF superfamily, or more specifically, the same IXc subgroup of the ERF subfamily. Transient expression experiment revealed that CsERF protein was localized in nuclei. Quantitative real-time PCR results showed that the expression of CsERF was induced not only by various stresses including salt, dehydration and cold, but also by stress-related hormones, such as ethylene, jasmonic acid and abscissic acid, with ethylene and cold as the two most potent inducers. Its ethylene induction could be blocked by 1-MCP, indicating ethylene signaling pathway was required for its activation. Overexpressing CsERF conferred tobacco plants with much stronger tolerance to chilling stress, and activated constitutively four indicator genes: two cold responsive transcription factor genes, NtCBF1 and NtCBF3, and two cold-induced genes, NtERD10B and NtERD10C. Under cold treatment, proline content and superoxide dismutase activity increased more rapidly and were much higher in overexpression lines than in wild type. These data suggest that CsERF plays a role in cold response in addition to the roles shared with its ortholog ERF1. (C) 2014 Elsevier B.V. All rights reserved.